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post #2701 of 17704 Old 09-04-2005, 05:19 PM
 
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Thanks for the comments on why antennaweb may be using pessimistic modeling. Even as an eletrical engineer with some RF experience, I am too lazy to try to dig into the reception modelling described here .

So question. Has anyone tried the low-noise amps from Research Communications? I have gone to their web site but it is hard to figure out how to buy one of these. I have an email into them. When testing, I got a marginal signal on King-DT but not enough to get a lock on it. I am hoping that the 1.6db gain over the 7777 pre-amp may do it for me. What you all think? ANd doesn't anyone in US make a very low-noise amp so I don't have to import this darn thing?

Amir
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post #2702 of 17704 Old 09-04-2005, 05:25 PM
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Quote:
Originally Posted by holl_ands View Post

The first reference (sec 73.683) lists the Grade A and Grade B contours for analog NTSC.
They are the same as have been used for many years (decades?) now.
Where's the 20 dB difference?
DTV Contours are 28 dBu (CH2-6), 36 dBu (CH7-13) and 41-20*log(615/Fc) dBu (CH14-69).
But you have to know that NTSC power is always measured with a peak reading meter, whereas DTV power is measured with an average reading meter.
That means that NTSC peak power must be 8+ dB higher than DTV average power to provide the same average receive signal.
DTV also requires a much lower SNR than NTSC.
The seemingly lower DTV Contour levels were postulated to provide the same number of households with "acceptable" performance as a Class B NTSC contour.
And in many tests people have found that DTV actually does provide equal or better reception under these constraints.
...
The FCC has NOT endorsed using the ILLR prediction program to determine whether you can theoretically receive on-air signals,
and if not, use those results to justify a Satellite waiver.

Hiring someone to make actual signal measurements has been endorsed,
give or take some lawyerly mumble jumble that I guess so far has succeeded
in putting Satellite waivers into a semi-permanent holding pattern.

Well, it looks like an oops on my part for the signal strength numbers. I may have been confused when I read quickly because all around that table it is talking about ATSC. That rule also states the following:
" (d) For purposes of determining the
eligibility of individual households for
satellite retransmission of distant network
signals under the copyright law
provisions of 17 U.S.C. 119(d)(10)(A),
field strength shall be determined by
the Individual Location Longley-Rice
(ILLR) propagation prediction model.
Guidance for use of the ILLR model for
these purposes is provided in OET Bulletin
No. 72. This document is available
through the Internet on the FCC Home
Page at http://www.fcc.gov. "
Which does sound like the fcc endorses ILLR for determining distant network eligibility. I think I was confused by looking for the levels for the SHVIA eligibilty and those still seem to be based on Analog reception which is why when I looked up the levels I got the Analog numbers. I should have known it was referring to analog reception because I knew they were currently basing eligibility on NTSC not ATSC reception. My Bad. So, I guess the reason for the overly pessimistic antennaweb numbers remains a mystery.

- John
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post #2703 of 17704 Old 09-04-2005, 05:42 PM
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Quote:
Originally Posted by holl_ands View Post

Maybe you have some database search tricks???

Unfortunetly nothing too helpful that I've been able to find -- It certianly does take quite a bit of "nosing" around. I have found where your local stations are concerned, just being familiar with their current+past filings can save time later on. Otherwise , Sometimes, it can even be difficult to figure out with 100% certianity what operting permit(or Program Test Authority) the station is actually currently operating with.

I think Using the CDBS search page is especially "clumsy" for this application, although for other applications(such as looking for which stations filed First round conflict resolution forums) it can work quite well. But, Sometimes just figuring out which selections(including muliple ones) in CDBS searh page you have to make for the query to get the info you want in the drop down boxes is frustrating.

Over the past 4 years, I have been fairly regularly using "Search by radius" query function of TV query ( http://www.fcc.gov/mb/video/tvq.html ) for my location to the distance required(65km in my case) so all my locals stations pop up, while using the "detailed info+CDBS links) option and then checking the "application list" for new applications/info to look at which I'm interested in ... so, just being familiar with the past filings from the stations you are interested in saves time when looking at anything new ...

Also, certian things do stand out, which can speed things up a bit when you're trying to find what you are looking for ... For instance, A date of 6/23/05, and a status of either "approved" or disapproved" is currently indicated for the first round election form for every station I've seen. A file number designation with a "STA" in it is for a STA (unfortuently, as mentioned above they have not made any STA applications available). Also, the file number(in any case, for any application/filing submitted to FCC) itself will contain the date the filing was submitted to FCC. And of course, under "service", "DT" stands for applications related to the digital station, "DS" is STA DTV designation -- However(and this seems a bit odd) Although you will find all CP Apps, CP MOD apps, CP extension requests and "license to cover" apps, and DTV STA applications/extensions for DTV stations listed under either "DT" or "DS" for service ... Some other info pertaining to DTV stations, such as first round Elections are shown under "TV" service, which "normally" applies currently to the analog station ... go figure ..

------------------------------

By the way, predicted contour maps(for field strengths holl_ands mentioned above -- 41dbu for UHF, 36dbu for hi-VHF, 28dbu for lo-VHF) for DTV stations using FCC's contour methodology are also available via TV query+with use of the TV query and "Detailed info+CDBS links" option.

For instance, If I use TV query by callsign and choose detailed info+cdbs links option, I get these results for my query of "KFMB" :

http://www.fcc.gov/fcc-bin/tvq?state...&slon2=&size=9

As you notice, first, a detailed section of info for their analog station on 8 shows up, followed by info on KFMB-DT's licensed facilities, and for some reason, a construction permit filed in 2000, and granted in 2001(if you look at the application list and match up the file numbers). So, since there is no new "license to cover" the CP at bottom of list, I must assume they are operting with the parameters shown for the info concerning their "licensed" facilities.

So, In the list of links right under the info on their antenna pattern/etc, at bottom line of links, it says : Area : Then a link that says "Service Contour Map(41dbu). Click on "service Contour Map(41)dbu, and you'll see a map of the area(I've included URL to this below), including the predicted 41dbu contour for KFMB-DT's currently licensed facilities :

http://www.fcc.gov/fcc-bin/FMTV-serv...=DT492582.html

Doesn't look like anyone but the fish will be impacted by their -13.7db null to the west

Jeff
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post #2704 of 17704 Old 09-04-2005, 05:48 PM
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The FCC has tightened up the DTV minimum field strength rules for city of license -

Channels 2 through 6 were 28 dBu now 35 dBu
Channels 7 through 13 were 36 dBu now 43 dBu
Channels 14 through 69 were 41 dBu now 48 dBu

The 7 dB change was to account for their overly optimistic tuner noise contribution and their abnormally high antenna gain, among other things. (This is assumed because they never gave reason for the change.)

This is for the city of licence only. The Grade A and Grade B contours do no have a corollary contour in DTV.

Just a clarification....

Bob Chase
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post #2705 of 17704 Old 09-04-2005, 06:06 PM
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Thanks Bob -- Here is also a link with the info you mentioned straight from the "rulebook"(this seems to be well updated), part 73.625 :

http://www.hallikainen.com/FccRules/2005/73/625/

I also recall reading about that, I think in one of the more recent DTV transistion related R&O's, but can't recall which one ...

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post #2706 of 17704 Old 09-04-2005, 06:08 PM
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I see that my stored link to bsexton.com is no longer operational. Has that site moved, or is it gone? The last time I visited it, they had only analog signal strength info available, but it was still useful to the extent that one might use analog Grade B levels to roughly predict the location of the cut-off perimeter of similarly situated, full powered DTV transmitters.

To the extent that the participants in this thread desire to actually discern whether the ambient signal levels where they are located can be developed to a level at which reliable viewing can be sustained, I consider all of this to be an exercise in futility.

We rely on the antenna manufacturers for antenna gain information, but they are in the business of selling antennas, and thus will present whatever info they have on gain in the manner that justifies publishing the biggest possible gain numbers.

Gain is expressed relative to dipole or isotropic radiator, but, as I understand it, that just gives a measure of "no-load voltage" measured at the terminals of the active element. But when we try to determine the sufficient power level needed to assure reliable operation of our tuners, the sufficiency values we are given are expressed in referenced decibel millivolts, which is not so much a measure of voltage as it is a measure of wattage actually delivered thought the connected, referenced load.

When you place a load across an antenna active element in an RF field, the voltage drops somewhat. It is my understanding that the maximum power transfer will occur when the load impedance matches the source impedance, so a 300 ohm dipole will develop its maximum power in dBmV or dBm when impressed upon a 300 ohm load, but I don't know if the calculations contained in this thread incorporate the voltage drop that occurs when the active element is loaded.

Even if they do, or even if there is an accepted value for the voltage drop that occurs when a 300 ohm dipole drives an optimal load (I'll guess 3dB, because half the voltage drop occurs across the load and the other half occurs across the source), the signal maximizers here often try to reduce the "balun loss" by using zero loss coax baluns, but such a balun may have the adverse consequence of reducing the efficiency of the reception loop, since a 75 ohm load will suck down the voltage level of a 300 ohm source more than a 300 ohm load will. With 60 cycle transformers, this effect is significant. Maybe at RF frequencies it is, for some reason, insignificant, but I don't know that to be the case. It may well be that the reduction measured in dBmV or dBm caused by the impedance mismatch of loading a 300 ohm dipole with a 75 ohm load is greater than the saving of that no-loss, tuned coax balun versus the much vilified, "ferrite" balun.

I also believe that the frequency response of tuners is likely to vary by several dB over the input spectrum range. I place no more stock in a manufacturer's claim that its tuners have noise figures of 9 or 10 dB (when they even bother to publish them) than I do in the published loss figures that Channel Master and Winegard give for their baluns, as anyone who has tested them knows that they vary by several dB over the broadcast spectrum.

I also am skeptical of one being able to rely on an S/N ratio to be able to reliably predict uninterrupted decoding. Any analysis of S/N ratios that suggests that 15.9dB is the threshold level that will get us the performance reliabilty we desire is really making assumptions regarding the nature of the variation in noise as it occurs in nature. Sure, we can degrade a signal with our flat, white noise generator until it fails to be decoded, and we might establish, from that, a consistent S/N minimum value that can withstand the effect of flat white noise degradation, but real noise occurs in bursts that have multiple dimensions of frequency, amplitude and duration, and it is the unique collective effect of each noise invasion that determines whether the frame being processed is corrupted beyond repair.

FWIW, someone once posted in these forums that the critical data within the 8VSB signal has been arranged such that it would tend to be relatively immune to the degrading effects of the co-channel analog picture carrier at +1.25Mz, and in fact, he said that the 8VSB signal can supposedly withstand an NTSC peak that is within 2dB of the RMS value of the 8VBS plateau. Maybe someone here with more time on his hands than I have could experiment with that and gradually increase the value of his own, modulator-generated NTSC co-channel to see how robust the 8VSB is when subjected to that kind of interference which does occur naturally, but which is not best analyzed by just measuring the 6Mz bandwidth RMS value of the NTSC signal.

Nitewatchman has mentioned that he has experienced disruptions on channel 10 from lightning strikes, and another forum member from Northampton, Massachusetts reported similar lightning disruptions on channel 11. It could be that lightning noise is the achilles heel for VHF highband, just as some kind of terrestrial impulse noise seems to wreak havoc on VHF lowband channels 2 and 3. Or it could be that our sample of two unhappy campers is statistically insignificant.
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post #2707 of 17704 Old 09-04-2005, 06:14 PM
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Quote:
Originally Posted by amirm View Post

Thanks for the comments on why antennaweb may be using pessimistic modeling. Even as an eletrical engineer with some RF experience, I am too lazy to try to dig into the reception modelling described here .

So question. Has anyone tried the low-noise amps from Research Communications? I have gone to their web site but it is hard to figure out how to buy one of these. I have an email into them. When testing, I got a marginal signal on King-DT but not enough to get a lock on it. I am hoping that the 1.6db gain over the 7777 pre-amp may do it for me. What you all think? ANd doesn't anyone in US make a very low-noise amp so I don't have to import this darn thing?

Amir

Of course I have had to edit my post because my guess about antennaweb was wrong. In the HD hardware forum ctdish has posted that he will be trying out a low noise amp soon. His antenna array is on a tower so it may take him awhile to try it. The posts below about pre-amps not meeting noise specs makes me suspicious of manufacturer's specs. I have seen some posts in the Hartford thread about people who bought the research communications pre-amp not getting better results so they wanted to sell the amp. I would think a more effective way to get more signal is to move the antenna. If it isn't blocked by anything close that would probably mean going higher.

- John
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post #2708 of 17704 Old 09-04-2005, 06:24 PM
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My TV has a read-out of the AGC value for a channel. I am thinking that if I tune to an empty channel I might be able to use this to compare pre-amps. Since the pre-amp gain would also affect the AGC value I need a relative measure of pre-amp noise. With satellite dishes you can measure the noise increase between pointing the dish at the empty sky and the sun to get a figure of merit for the antenna plus pre-amp. I wonder if a similar method might work with a good antenna. Normally a TV antenna's temperature is set by the ground temperature (I think) but what if you pointed it straight up and measured an empty channel's signal level and then pointed it straight down and repeated the measurement? I would think that if a pre-amp had a very low noise factor like 0.5 then you should see a bigger difference. Of course this would require an antenna with a good front to worst-case rear spec and a truly empty channel to work. Or is there some reason the antenna temperature wouldn't tend to track the sky vs sun or ground temperature like it does with a satellite dish?

- John
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post #2709 of 17704 Old 09-04-2005, 06:44 PM
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Quote:
Originally Posted by Nitewatchman View Post

Thanks Bob -- Here is also a link with the info you mentioned straight from the "rulebook"(this seems to be well updated), part 73.625 :

http://www.hallikainen.com/FccRules/2005/73/625/

I also recall reading about that, I think in one of the more recent DTV transistion related R&O's, but can't recall which one ...

This rule does indicate that the height above average terrain is used to compute the service area contours doesn't it? I have always thought that that is how the coverage maps from the TV query site are generated. If true then of course they are not very useful as compared to the ILLR model for predicting reception for a given location. I wonder then if those field levels have any applicability to ILLR? I guess a good technique for an individual to determine the required field strength with ILLR is to use holl_and's spreadsheet with the details for their installation.

- John
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post #2710 of 17704 Old 09-04-2005, 06:51 PM
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Quote:
Originally Posted by AntAltMike View Post

I see that my stored link to bsexton.com is no longer operational. Has that site moved, or is it gone?

What you are talking about from the old bsexton URL was available via a "free coverage maps" link from this site for a time, but I believe it is now gone "completely" :

http://www.ardman.net/

Quote:
Originally Posted by AntAltMike View Post

Nitewatchman has mentioned that he has experienced lightning disruptions on channel 10 from lightning strikes, ..... Or it could be that our sample of two unhappy campers is statistically insignificant.

It's insignificant in my case. I am certianly not"uphappy camper" becuase of TWO dropouts due to TWO VERY NEARBY(to the receive antenna) lightning strikes Over FOUR YEARS of viewing this station.

It's statistically insignificant even concerning my DTV reception over the past four years during thunderstorms occuring at MY location, and if my reception was the only "sample" available ...

To further clarify .... I have viewed the local VHF DT station on 10 through numerous storms(or storms in the signal path) and it wasn't a problem, at all.

Now, also, when I said very nearby lightning strikes, I mean I could hear the sound of the air being disturbed at the exact moment of the strike, and the flash was VERY bright(inside a room with blinds and shades that let in very little light with my eyes focued on the TV which is nowhere near any windows) ..... and I have no doubt I would have seen quite a bit of "static" IF I had been watching a UHF analog station at the time ....

Add in the other FOUR reception dropouts(to the DT on 10, and a DT on 24 NONE on my other 12 local DTS) I've seen due to "extreme" co-channel interference during abnormal signal propagation OVER 4 YEARS TIME, adding up to a total of about 6~8 seconds of "disrupted viewing" on 14 local DTV stations(I was OTA only viewer until adding E* service a year ago, so this wasn't just a few hours of watching local DTV stations a week), and I am certinaly in NO shape or form a "unhappy camper" when it comes to DTV ....

Update:

That being said, we have had a number of posters on our local thread which have seemingly ran into difficulties with reception of this station not only involving lightning, but man-made impulse noise and other RFI which we tend to think of being much more of a problem on Lo-VHF. I say seemingly, however as it is often difficult to detirmine with any sort of certianity via posts on this forum what "difficulties" are causing reception problems in any specific case.

Quote:
Originally Posted by AntAltMike View Post

To the extent that the participants in this thread desire to actually discern whether the ambient signal levels where they are located can be developed to a level at which reliable viewing can be sustained, I consider all of this to be an exercise in futility.

While I tend to agree somewhat with this assesment in a general way : Nevertheless I think some of the details which have been provided here can be useful to some for various reasons. Also, certianly a Longely-rice study even without "extra precise information" on such factors as receive antenna gain can be beneifical for those in terrain obstructed receiving locations who want to get at least a bit of an idea of whether or not they may have a chance at reception of a given station.

Jeff
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post #2711 of 17704 Old 09-04-2005, 07:04 PM
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Originally Posted by AntAltMike View Post

...

To the extent that the participants in this thread desire to actually discern whether the ambient signal levels where they are located can be developed to a level at which reliable viewing can be sustained, I consider all of this to be an exercise in futility.

...

I think you are being overly pessimistic. Programs like radiomobile are readily available on the web to predict the transmission loss of radio waves between the transmit and receive antennas and statistical modelling of various disruptions has always been a part of reception studies like were done in creating Longley-Rice. You can also download free or cheap antenna modelling software like 4nec2 or eznec or multinec plus antenna models from the hdtvprimer web site to get good estimates of real antenna power gains. Or, just look at the plots at hdtvprimer. There are also balun loss and pre-amp noise measurements available. So if you are using a balun and pre-amp with independently measured performance then predictions should be possible. The final piece to the puzzle of the needed fade margin for a reasonable time reliability can be determined by comparing prediction results to experience the way holl_ands appears to be doing.

- John
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post #2712 of 17704 Old 09-05-2005, 08:28 AM
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But the relatively new mission is, we are now trying to estimate the performance margin necessary to assure glitch-free decoding of digital images that persist for as long as one second at a time and intervals of audio disruption that may endure for even longer, rather than to minimize the slight visible degradation of analog pictures that persist for only 1/30th of a second.

We can calculate what it takes to develop a TASO Grade 1 analog picture, and, in most situations, our input data are accurate within a few dB, and even if it isn't, most of us can't discern the difference between a picture with, say, a 43dB S/N ratio rather than a 46dB ratio. If a plane files overhead and causes a reflection that lasts one frame on an analog picture, we probably won't notice it, any more than people noticed the "subliminal" advertising that may or may not have been shown in movie theaters (and in a great Colombo episode) back in the 1970s, and we may or may not even notice one frame of impulse noise speckles on an analog program if the background was solid and still versus complex and moving.

While we engineered performance margins that gave us Grade 1 or 2 analog pictures, when those systems failed to meet that margin we usually didn't notice, and when we did notice, we usually didn't care, and so we really have no idea how often those reception links failed to attain our calculated threshold signal quality levels, but when the reception link fails to develop sufficient signal quality for a minuscule but critiical interval in the reception of the data stream, we notice.

I will not, under any circumstance, install a residential off-air reception antenna as a subcontractor because, if the customer ever has a one second freeze-up on his $6,000 plasma display which is part of his $20,000 home theater, he will be strongly inclined to call his contractor to complain, who, in turn, would be inclined to call me to make sure that I didn't do something wrong. I can take on that kind of responsibility from my own customers because most of them are commercial, and as far as the few residential installations I did are concerned, I made them acknowledge that I had told them that every once in a while a glitch could occur and that it didn't mean that their system needed on-site service, in-warranty or otherwise, but because I couldn't similarly browbeat them as a subcontractor, I simply decided not to take them on as customers.


I've installed master antenna systems with multiple antenna arrays in about a dozen high-rise buildings and I wish I could say that I am certain that my installations have been glitch free, but the fact it, I so thoroughly conditioned the customer, meaning the management, to screen out complaints that I really can't say for sure that all of my systems have been as reliable as they appear to be. I think they have been, because I have a lot of S/N margin to work with in my market, but I understand that by having effectively preempted potential complaints, I just might have buried a few of them.
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post #2713 of 17704 Old 09-05-2005, 12:30 PM
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This post addresses several areas of HDTV reception: Finding True North, ATSC Reception Test Equipment, Satellite Dish Aiming, Paint, Washers and Antenna Pictures. See attached PDF files.

Finding True North
The simple way is to use a good magnetic compass. A suitable compass can be found at your local Wal*Mart in the Sporting Goods section. You will need to account for your Magnetic Declination and that can be computed by NOAA Magnetic Declination site.

The sun can be used to find true north, go to NOAA Weather site, enter your nearest city & state, then select Local Climatology, then select the nearest location to you under the Daily Climate Reports. There should be a section that will list the Sun Rise and Sun Set times. Format three cells in Quattro (or Excel) in 24 hour time mode. Enter Sun Rise as XX:XX:XX and Sun Set as YY:YY:YY. In the third cell enter this equation: (((Sun Set-Sun Rise)/2)+Sun Rise) This will calculate your local High Noon. At this time a vertical (plumb) pole or object will cast a shadow on a level surface (tangent) that points due North. Note: when the sun is close to The Tropic of Cancer the shadows will be short in the USA.

The North Star will also get you close. At night, position yourself so your antenna mast is inline between you and the North Star, now mark a spot at your feet. During daylight you can point your antenna boom to the spot previously marked as your starting reference.

Problematic DTV reception:

There will be situations were receiving DTV stations will be difficult. Without proper test equipment the most one can do is place and aim their antenna by trial & error. In most cases analysis with instruments should show if reception at a particular location will be feasible. At minium, the test unit has to have a spectrum analyzer with sufficient resolution and display to show echo nulls, desired channel flatness and other signal degradation. Unfortunately these instruments are fairly expensive and beyond the reach of many (most) serious hobbyists. Listed below are several devices that are designed to analyze DTV signals. A general purpose Tenma Spectrum Analyzer is included because it is relatively inexpensive for this class of equipment. Please note this unit does not cover all the L-Band frequencies and may not be suitable for common satellite use. The Sencore AT1506 seems to be the most advanced DTV analyzer, but I think it is being phased out of their product line.

DISCLAIMER: I have no experience or affiliation with any of the devices listed below except as noted.

At work we had a Tektronix RFM151 that I used for DTV signal evaluation. It appears to be available from Tempo as the Signal Scout RFM151. This was a fine unit but the operation was not very intuitive.

Tempo Signal Scout RFM151, Sencore AT1506, Sencore SA 1454, Sencore SLM 1456, Leader LF 983 (Has been discontinued??) Tenma 72-6696 1GHz Spectrum Analyzer. Added: BK Precision Model 2630 Spectrum Analyzer and Sencore DTU-234 RF Probe with optional software.

Peter Putmans comments on DTV reception, spectrum analyzers, and some antenna test. HEAVY METAL, PART I, Spectrum Analyzers. More Antenna Test by Bob Chase using a spectrum analyzer.

The file Coaxial Balun-0001.PDF contains a drawing of resistive pads to convert the 50Ω input and tracking generator output of a spectrum analyzer to 75Ω in and out. A Tapered T Attenuator and a 75Ω, 43dB Symmetrical T Attenuator convert the output of a 0 dBm, 50Ω tracking generator to 0 dBmV, 75Ω. The attenuation of the Tapered T Attenuator was chosen so the value of R2 was 0Ω and therefore eliminated. Most outs will be adjustable in 10 dB steps so you could make the Symmetrical T Pad 13 dB and set the generator to -30 dBm. The resistors should be Dale/Vishay RN60 series or better, the 1Ω could be hard to find and one may have to use a thick film resistor. The input to the analyzer has a single 25Ω resistor added in series with the input. Just add 50.5 dB to the analyzers reading to convert to dBmV, i.e., -63.7 + 50.5 = -13.2 dBmV. The operation of a 1/2λ coaxial and a ferrite transformer balun (set to ideal) is included. The 1/2λ coaxial balun is in purple and the ferrite transformer balun is in green.

Satellite Dish Aiming
Tic Mark Spacing-0001.PDF has degree markers for three common use pipe sizes. When printing this sheet make sure the Shrink to Fit option is not checked. A line that is 6 inches in length is at the top and is your reference, measure to make sure that it is the correct length. I print these on 24lb. paper, cutout the desired marker and attach to my dish pole. I cover them with clear weather proof tape (Frost King), see Antenna-0001.PDF for pictures.

Aim your LNB boom arm due South (those dishes with skew should be set to none or neutral skew), take a common paper clip and straighten one leg and temporally tape it to your dish incline bracket so that it is inline with a tic mark. Make a mark where the dish should be rotated to and rotate the dish so the pointer (paper clip) is at the reference mark you made (i.e., your location requires 213° W, 213-180 = 33° West rotation from due South [clockwise, looking down on the dish]). Set the elevation (and skew if multi satellite dish). If done correctly you should have a signal from the desired satellite(s). Tweak the azimuth and elevation for best signal, the skew should not be changed. For folks with small aperture dishes and using linear LNBs, set the skew of your LNB that corresponds to your location and desired satellite. Folks using an H-H motor mount should have their LNB skew set to 0°.

Satellite Dish Paint and Washers
Rust-Oleum Smoke Gray 7786 [20066 77868] paint is a very close color match to the Winegard and KTI satellite dishes that I have. This paint is very slow drying. To touch-up minor scratches I tighten the cotton of a cotton swab, spray the swab and apply.

To minimized scratching the elevation marking on my satellite dish incline brackets used to adjust the dish elevation I procured 1/4 (≤ 76CM dish) and 5/16 (≥ 1M dish) inch nylon washers and placed between the bracket and flat washers.

Pictures
Antenna-0001.PDF contains four pictures of my satellite dishes and antennas. I live in a condo and have very limited use of space. Upper Left: Winegard DS-3100 for Ku satellite (AMC-3 for PBS HD). KTI for Dish Network at 110° and 119°. Upper Right: Rear view of Winegard DS-3100. All the mounting items were fabricated by me from items available at the local building supply and online. 2-3/8, 16ga. fence post, 1-5/8 (actually 1.66") 17ga. fence post, 3/4 EMT, and treated lumber. The hardware items are: stainless steel, galvanized or Grade 8. Lower Left: Winegard PR-9032 UHF antenna, RCA dish for Dish Network at 61.5°. Lower Right: Closeup of the PR-9032.

09-19-05 Added to analyzer list
10-04-05 Added link to Bob Chase antenna test

 

Coaxial Balun-0001.pdf 21.3515625k . file

 

Tic Mark Spacing-0001.pdf 13.1396484375k . file

 

Antenna-0001.pdf 364.7939453125k . file
Attached Files
File Type: pdf Antenna-0001.pdf (364.8 KB, 129 views)
File Type: pdf Tic Mark Spacing-0001.pdf (13.1 KB, 112 views)
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post #2714 of 17704 Old 09-05-2005, 02:28 PM
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I am relatively new to HDTV programming through my satellite service. However I think I am just about ready to roll. My question is on getting broadcast HD channels. I have been hearing I need to set up an antenna and connect it to the HD receiver. As a test, I tried hooking an indoor antenna to the HDTV itself located in my basement however it was quite fuzzy.

In the stores, I see large antennas for mounting on the roof or on the side of the house and I also see smaller ones for indoors. What is the recommendation for receiving HD broadcast channels? According to the first post I saw, bigger antenna, higher up (roof mount). Any thoughts? Thanks.


Carl
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post #2715 of 17704 Old 09-05-2005, 02:40 PM
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Quote:
Originally Posted by deconvolver View Post

My TV has a read-out of the AGC value for a channel. I am thinking that if I tune to an empty channel I might be able to use this to compare pre-amps. Since the pre-amp gain would also affect the AGC value I need a relative measure of pre-amp noise. With satellite dishes you can measure the noise increase between pointing the dish at the empty sky and the sun to get a figure of merit for the antenna plus pre-amp. I wonder if a similar method might work with a good antenna. Normally a TV antenna's temperature is set by the ground temperature (I think) but what if you pointed it straight up and measured an empty channel's signal level and then pointed it straight down and repeated the measurement? I would think that if a pre-amp had a very low noise factor like 0.5 then you should see a bigger difference. Of course this would require an antenna with a good front to worst-case rear spec and a truly empty channel to work. Or is there some reason the antenna temperature wouldn't tend to track the sky vs sun or ground temperature like it does with a satellite dish?

I would be careful about making any conclusions based on the AGC value in your TV Tuner.

I would hope that most modern designs apply AGC to the RF front end, but some may not.
The best RF AGC would be developed based on signal overload within the RF bandwidth,
which would include strong RF signals several channels away, rather than the heavily filtered
IF bandwidth that may only include adjacent channel signal levels.
But most modern designs develop AGC in the IF bandwidth and then apply that same signal to both RF and IF.

Several of the few detailed designs that I've seen disclosed employ either "stepped" AGC schemes
that apply 10, 20, 30 or 40 dB attenuation or employ linear AGC control range up to about 40 or 50 dB.
Below a (sometimes variable) signal threshhold, the AGC attenuation is set for minimum,
depending on the dynamic range of the RF amplifier for the first several decades of signal strength.
Above the maximum attenuation setting, the amplifier responds to increasing signal levels with more intermods.

This latter effect will mean that the displayed AGC value will be at minimum attenuation
for a fairly wide range of low level input signals.

======================================================
Radio Telescope systems regularly check to make sure that the sky noise temperature is close
to their specified minimum and then can scan around to find the direction of unwanted interference.

So can you do the same with a Preamped TV antenna? Probably not.
A TV antenna has a fairly wide beamwidth and significant sidelobes that let in multipath reflections
from all sorts of unexpected directions.
Unless you are in the Australian Outback, the Preamp will almost always be presented
with moderate to strong signals that will generate intermod products that are above the noise floor.
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post #2716 of 17704 Old 09-05-2005, 02:52 PM
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Quote:
Originally Posted by chwilson0607 View Post

I am relatively new to HDTV programming through my satellite service. However I think I am just about ready to roll. My question is on getting broadcast HD channels. I have been hearing I need to set up an antenna and connect it to the HD receiver. As a test, I tried hooking an indoor antenna to the HDTV itself located in my basement however it was quite fuzzy.

In the stores, I see large antennas for mounting on the roof or on the side of the house and I also see smaller ones for indoors. What is the recommendation for receiving HD broadcast channels? According to the first post I saw, bigger antenna, higher up (roof mount). Any thoughts? Thanks.


Carl

FUZZY??? You must have been watching an old analog TV station.

DTV signals display in either decimal (e.g. 5.1) or dashed (e.g. 5-1) format.
They are either extremely sharp or they suffer from blocks of pixels being scrambled
or when it's really bad, signal dropouts that can last for seconds to minutes at a time.

You need to get the antenna out of the basement and as high as possible.
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post #2717 of 17704 Old 09-05-2005, 04:39 PM
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Quote:
Originally Posted by chwilson0607 View Post

I am relatively new to HDTV programming through my satellite service. However I think I am just about ready to roll. My question is on getting broadcast HD channels. I have been hearing I need to set up an antenna and connect it to the HD receiver. As a test, I tried hooking an indoor antenna to the HDTV itself located in my basement however it was quite fuzzy.

In the stores, I see large antennas for mounting on the roof or on the side of the house and I also see smaller ones for indoors. What is the recommendation for receiving HD broadcast channels? According to the first post I saw, bigger antenna, higher up (roof mount). Any thoughts? Thanks.


Carl

You can go to antennaweb.com and type in your address to get an idea of the digital channels that should be fairly easy to receive. The antennaweb prediction is pessimistic though so with a good antenna system (and antenna pre-amp for rural locations) you may be able to get more stations than antennaweb says. Some receivers can get both the old-fashioned fuzzy analog stations and the new digital ones, it is the digital ones that will be clear (and sharp when they broadcast HD like most major network affiliates mostly do during prime time).

- John
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post #2718 of 17704 Old 09-05-2005, 05:19 PM
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Quote:
Originally Posted by holl_ands View Post

I would be careful about making any conclusions based on the AGC value in your TV Tuner.
...
======================================================
Radio Telescope systems regularly check to make sure that the sky noise temperature is close
to their specified minimum and then can scan around to find the direction of unwanted interference.

So can you do the same with a Preamped TV antenna? Probably not.
A TV antenna has a fairly wide beamwidth and significant sidelobes that let in multipath reflections
from all sorts of unexpected directions.
Unless you are in the Australian Outback, the Preamp will almost always be presented
with moderate to strong signals that will generate intermod products that are above the noise floor.

Thanks for the info holl_ands. The AGC value seems different for each channel and is much higher for empty/very weak channels. Given how you say most AGC's work I suspect that my TV's AGC readout would not work well enough as a signal level meter. My house is in a bit of a hole so I don't have a direct path to any station. For instance the radiomobile prediction for my strongest digital UHF station is +23 dB above a threshhold of 39 microvolts/meter. I had hoped that intermod products would be negligible so the noise floor for some weak stations would be the antenna thermal noise+cascaded noise factor. This might be true for a few select regions of the UHF band which seem to be very empty for my location. I still expect that you are right that since I don't have an under-illuminated dish for an antenna I will see lots of noise level variation depending on leakage of energy through minor lobes and wouldn't be able to sort out when the noise level is mostly determined by pre-amp noise even with a good signal level meter.

- John
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post #2719 of 17704 Old 09-05-2005, 08:16 PM
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Quote:
Originally Posted by holl_ands View Post

FUZZY??? You must have been watching an old analog TV station.

DTV signals display in either decimal (e.g. 5.1) or dashed (e.g. 5-1) format.
They are either extremely sharp or they suffer from blocks of pixels being scrambled
or when it's really bad, signal dropouts that can last for seconds to minutes at a time.

Second that! Over this long weekend, I built a VERY makeshift dipole and hooked it up to my new ATSC PC tuner card. The antenna is U-G-L-Y, masking taped to a wall, aligator clips connecting it to the inner wire on a run of coax strewn across the floor to plug into the card...

I checked a few UHF NTSC channels first on a regular TV, to see if my antenna worked at all, it did, but the picture was less than perfect. Good, antenna works. Now connected the antenna to the ATSC tuner card... WOW!! Crystal clear SDTV on 62.1 and when I tuned to 62.2, an HD channel, even clearer HDTV. My wife thought I was a little crazy the way the "lab" looks right now, but even she was quite excited about the picture quality and couldn't believe it was coming in over that little makeshift antenna.

On a side note, I have really enjoyed all the conversation about the SNR equations. Some of it even made sense ... I will definately factor in the antenna pattern. Luckily, many transmitters in my area are non-directional. Holl_ands and Nitewatchman in particular, thank you! I'm not going into this expecting absolutely correct results, but it will be nice if I can get somewhat more accurate results from modeling than what antenna web provides. And if both my modeling and antenna web say my location is a no-go, then I know not to bother buying an antenna at all. My personal feeling on drop-outs is that a tiny drop out here or there will be okay by me, much better than watching BLURRY analog NTSC ALL THE TIME on a 42" plasma. Just sayin' ;-)

Check out my Cozy Room within a Room Theater Build... in progress and closing in on completion.
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post #2720 of 17704 Old 09-05-2005, 09:08 PM
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Quote:
Originally Posted by bmcent1 View Post

but even she was quite excited about the picture quality and couldn't believe it was coming in over that little makeshift antenna.

That's the kind of stuff I like to hear about !

-------------------------------------------

I was thinking how much easier this might be for many folks if stations would post predicted coverage map on their website of their service area based on Longely-rice studies, perhaps with simply labled shaded areas such as "fringe signal area", "strong signal area", "big honkin' single channel antenna array area"(or "good luck" area)/ etc .....

Jeff
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post #2721 of 17704 Old 09-05-2005, 10:03 PM
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Excellent post Wendell. The North star Polaris is @ Right Ascension 02 : 31 : 50.5 (h:m:s), & Declination +89 : 15 : 51 (deg:m:s) - pretty close.

Those spectrum analyzers seem to be $2100-3000 new, looks like there are deals on used & refurbs. Also the Tektronix RFM151 Signal Scout Cable VRF Analyzer, I guess both brands now owned by Textron.

Oil based enamels for metal are ideal for outdoor durability like the Rust-Oleum. I use same paint, also different colors & spray can:

Rust-Oleum Clean Metal Primer 12 oz spray #7780-830 white, clean metal
Rust-Oleum Clean Metal Primer rust inhibitor 1 quart #7780-504 white, clean metal
Rust-Oleum Rusty Metal Primer rust inhibitor 1 quart #7769-504 white, clean metal
Rust-Oleum Protective Enamel oil-based enamel 1 quart #7779 many colors
Rust-Oleum Professional Enamel oil-based enamel 1 gallon #7779 many colors
Rust-Oleum Gloss Protective Enamel 12 oz spray #7770-830 many colors
Rust-Oleum Gloss Hammered Metal Finish enamel 12 oz spray #7210-830 black, gold, green
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post #2722 of 17704 Old 09-06-2005, 12:33 PM
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Hey, guys, I bought a CM4228 and get signal strength mostly in the 70s (some 80s) per the HD Tivo. But I'm still concerned about dropouts. We saw one yesterday (could be a transmission glitch, duno). I have to go topside to remove an old antenna anyway, so I'm wondering a preamp might not help me.

I'm about 25 miles from the main tower and 20 from the secondary tower which is on a similar line. There is one VHF station on the secondary tower (soon) and the rest are UHF.

Would a 7777 help? Is a 7778 the better choice as lower gain seems all that might be needed? Is either overkill? Pleas help!

There's a saying about "everything in moderation". If only it was applied to well, you know...
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post #2723 of 17704 Old 09-06-2005, 02:12 PM
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Does a person need an HD antenna to HD quality reception? Or does a strong UHF and/or VHF antenna accomplish the same result?
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post #2724 of 17704 Old 09-06-2005, 02:35 PM
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Their is nothing special about any antenna labled HD. Since the HD channels are in the same bands as the analog channels any good antenna will do. Generally a large antenna will be better than a small one for a given band. If your analog chanels look good especially UHF, you are probably good to go. John
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post #2725 of 17704 Old 09-06-2005, 03:24 PM
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It sounds like you're doing fine already. With those numbers, occasional glitches are not a strength problem. You're just about at the inside limit for a preamp and the HR10-250 is an easy receiver to overload. If you want to try something, a 15 db preamp rather than a mid 20s might be okay. If I were you, I'd leave well enough alone. I'm 11mi away with 90-94 for numbers and I get more glitches than you do.

Pat

While I may link to and mention products as examples, I don't recommend specific products.
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post #2726 of 17704 Old 09-06-2005, 05:07 PM
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Quote:
Originally Posted by AntAltMike View Post

We rely on the antenna manufacturers for antenna gain information, but they are in the business of selling antennas, and thus will present whatever info they have on gain in the manner that justifies publishing the biggest possible gain numbers.

Gain is expressed relative to dipole or isotropic radiator, but, as I understand it, that just gives a measure of "no-load voltage" measured at the terminals of the active element.

When you place a load across an antenna active element in an RF field, the voltage drops somewhat. It is my understanding that the maximum power transfer will occur when the load impedance matches the source impedance, so a 300 ohm dipole will develop its maximum power in dBmV or dBm when impressed upon a 300 ohm load, but I don't know if the calculations contained in this thread incorporate the voltage drop that occurs when the active element is loaded.

The biggest problem is that most manufacturers don't publish gain vs freq.
And then there is the trick of citing the maximum (vice average) gain value.
And/or using dBi rather than the usual dBd number for another 2.15 dB inflation.
I usually assume they've done both (like DAT-75) if they don't specify otherwise.

I've posted a comparison chart between actual measured antenna gain
vs manufacturer spec sheet data vs NEC Simulation results for both the
Channel Master CM4228 and the Winegard PR8800 8-Bay Antennas in
the fol. thread:
http://hdtv.forsandiego.com/messages...tml?1126050076
The spread sheet summarizes spec sheet info for many different, mostly UHF, antennas.

Unfortunately, these are only two antennas tested by Kerry Cozad that also
have detailed frequency response specs released by the manufacturers.
Hopefully you will note that for both antennas, the actual measurements
were about 2 dB HIGHER than the spec sheet claims.

Also note for several antennas, the NEC Simulations underestimated gain below CH30.

Dielectric recently posted a white paper to accompany the vu-graph presentation:
http://www.dielectric.com/broadcast/...ntennas%20.pdf
Note measurements were conducted per IEEE-STD 149-1979 cited below.

===================================================
Antennas are measured with either a 75-ohm or 300-ohm resistive load.
Of course real Preamps and TV Tuners will exhibit a VSWR of their own,
but the antenna manufactures have no control over that aspect.

The applicable spec is ANSI/IEEE-STD 149-1979, "Standard Procedures for Antennas"
which you can buy on-line for not quite a "C" note or find a well equipped library.

Since that is usually not very convenient, here are some alternative links:
How to measure 50-ohm base station antennas, based on IEEE-STD 149-1979:
http://www.guerrilla.net/reference/a...-sept-1999.pdf
The Mexican government's adaptation of IEEE STD 149-1979:
http://www.justnet.org/pdffiles/N20402.pdf

Exercise for the (Norwegian) Student:
http://www.tele.ntnu.no/radio/fag/TT...atternMeas.pdf
using HP-9720C Vector Network Analyzer:
ftp://ftp.testequity.com/pdf/8719-22c.pdf
which has a VARIABLE input impedance from 0.001 to 1000 ohms, so there
is no need to use a balun or 75/50-ohm minimum loss pads.
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post #2727 of 17704 Old 09-06-2005, 06:57 PM
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hey guys,
Hope you guys can give me some advice. Live in Richmond and have two antennas. One toward the Richmond stations and one towards Norfolk. My son loves the WB and they are on channel 33. The antenna I have toward Norfolk is a antennacraft d9000 with 92 elements. It is manufactured by the same folks that make the radio shack antennas. I do know that it has a adverage gain of 9db but not what each channel gain is. I am able to pick up 33 fairly well at night and early morning but it gets unwatchable during the day with no audio. Norfolk is around 70 miles from my location. My question is that the antennasdirect xg91 gain on channel 33 is 15.7 and the 4228 is around 11. I am leaning toward the XG91 but may try both out and see which one does best with a uhf preamp. With these antennas and the higher gain do you guys think that I could get a watchable picture during the day? I figure having twice the elements for uhf and so much more gain that I should get a decent picture. Also I am confused. Antennaweb told me that the Norfolk stations are 136 and 137 degrees from my location but when I pointed my antenna to that degree mark I couldn't get a picture but when I pointed to 180-190 degrees I got the best picture. Also why does the picture detiorate during the day. All the literature I have read states it shouldn't. Any advice would be appreciated. Thanks Joseph
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post #2728 of 17704 Old 09-07-2005, 09:00 AM
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Quote:
Originally Posted by deconvolver View Post

I doubt that a different antenna in the same place will make a huge improvement over a CM4228. Assuming you already have a good non-overloaded pre-amp like a CM 7777 and interfering channels are not the issue then unless you can re-locate the antenna to a better (higher) place it will be difficult to go from an unusable to a good signal. How close to watchable is the station now? If it is not almost fine with a few too many dropouts then don't expect miracles.

Well I have a 7775 since all I am trying to receive is UHF. I was wondering the reading I have seen mentioned local hot spots as well as dips in signal. How far apart is channel 35? I believe it is around 500 Mhz so is this a single wavelength distance or what?
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post #2729 of 17704 Old 09-07-2005, 12:08 PM
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Quote:
Originally Posted by theroys88 View Post

My question is that the antennasdirect xg91 gain on channel 33 is 15.7 and the 4228 is around 11. I am leaning toward the XG91 but may try both out and see which one does best with a uhf preamp.

Kerry Cozad's actual measurement for CM4228 on CH32 was 14.7 dBd,
which is about 3 dB higher than the spec sheet info.

I don't know where you found the 15.7 dB from, but I suspect that it may be dBi (relative to isotropic)
rather than dBd (relative to dipole gain), such as is used by Channel Master and Winegard.
To obtain dbd from dBi, subtract 2.15 dB.

None of the XG91 websites cited in Nitewatchman's post #2599 on 8/31/05 indicated whether their antenna gain numbers were in dBi or dBd.
By looking at other simple antennas on the Funke website, such as the FM 2-element Yagi and VHF 4-element Yagi, it is clear that Funke uses dBd.

Their gain plot shows a gain of about 14 dBd on CH33 for the XG91 type antenna.

So they are within about a dB of each other on that channel and both have about the same shape to the curve and hence appear to be fairly close across the UHF band.
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post #2730 of 17704 Old 09-07-2005, 06:59 PM
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Quote:
Originally Posted by holl_ands View Post

So they are within about a dB of each other on that channel and both have about the same shape to the curve and hence appear to be fairly close across the UHF band.

I've been told by those with the expertise to know that the 91XG is a fraction better than the other common antennas (including the 4228.) I do know that for those with a rotor, there really is no reason to chance the 4228's sail-potential.
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