OTA recommendations for deep fringe - Page 2

Sorry to disappoint you folks but I removed my Winegard 4800 preamp. In it's place I added dual 20 db preamps, both in my basement neither on the mast yet.

Hooked up to my old LG tuner I got 2 more stations. So with 40 db gain I have no signs of overload on any station and getting 2 I could not get without the preamp.

Then hooked up a Zenith converter box and got another 8 channels solid.

I am only 11 miles from lots of powerful stations.

When you want to get stations at -80 to -100 dbm don't expect anything without preamps. If I run without them I lose well over half my stations! My weakest now that comes in good tvfool lists at -103 dbm. Strongest are listed at -41 dbm.

Excluding the grey ones weaker than -110 dbm I am getting all stations I expect except one marked with adjacent channel and cochannel issues.

Where I am I can get the -40 dbm range stations easy with just an indoor antenna (need either a preamp or it must be near a window.) but they still work good with my high gain and outdoor tower antennas. Without preamps I lose all stations weaker than about -60 dbm.

My new preamps are a Research Communications and then a Kitztech.
I have most all RG11 cabling. Several splitters before signals get to my tuners, so the overload issues would be the preamps mostly.

A friend of mine is even closer to the tv towers, about 5 miles maybe. He can't use dual preamps but his 4800 alone works well for him. Has a Parascope too.

Both in his case and mine there is no line of sight, which is why the locals are at -41 dbm.

I have to thank you folks for making me try this! I was actually trying to get overload to see how close I was to problems with only 28 db gain in the 4800!

And I am a bit amazed that ziggy29 can receive anything at the -100 dbm levels without a preamp! I never have even received signals at -75 dbm without a preamp using about 4 different antenna setups.

Thanks Rick0725 for the calculator, I will try that out later.

But quickly let me say I am not hiding anything that I know of. One difference for me from Texas I expect is we have more hills here that give me excessively bad multipath with quite a wide range of delays. Often see multiple ghosts on analog. With my older tuners 2 degrees errror from optimum aim can lose me a channel and hang up the tuner so I have to power down and up. Wet ground also requires re-aiming my antenna for most channels. I expect this has a significant impact.

I also note with tvfool calculated for my work location which is about 3 miles from my house the Needham MA tower signals (main Boston stations) come in at over 10 db stronger. My line of sight is also blocked by hills fairly close in that could cut my signals maybe more than the model. I think the hill blocking me from Needham is about 3 miles away.

I was surprised too that dual 20 db gain preamps don't seem to overload.

My 4800 was only tried after using no preamp and then 2 different ones near 20 db from Channel Master and Winegard. It got me better results. 2nd best was the lower gain Winegard. The Channel Master one was useless though it seems generally highly rated.

It is true that I benefit for the NH stations (which I want the most) by having them opposite to the strong stations. However the RI and NewBedford weak stations are also coming in right in line with the strong Boston ones.

Back when I first set up my antenna in 1999 or so, digital was much weaker on all channels and I would lose about 3 key stations without the 4800 preamp use.

Today I need all this stuff to get PBS (HD feeds) and some other NH stations.

In CA can receive all but 1 local station w/o a pre-amp from the 4228 in my attic, but I suspect my signals are stronger than the TV Fool plot indicates (-88 to -102). I get about 80% with a rabbit ear/loop combo in my window, un-amped and all of them with a 4221 in a window. Not having any local stations within 50 miles helps.

In CT, I'm lucky to get a whisper w/o a pre-amp on the distant stations in the -100's. However, I'm dealing with local stations within 15 miles at this site and the 7777 was most definitely overloading (and will be replaced).

There's no substitute for actual tests, but TV Fool is still an excellent tool.

I don't see where this spreadsheet takes into account the difference between NTSC peak power and ATSC average power. I'm assuming this is an important difference when considering overload or am I missing something?

The calculator looks useful as a start except I don't have excel. But there are limitations.

1 I see vast differences as to what works for both preamps and antennas with each of my different tv tuners, none of which have any proper specs.

2 It doesn't take into account the probably 20 db of signal I lose just from the multipath canceling chip. I realize this doesn't help as far as the preamp overload but it does absolutely change the amount of IM you may have to live with to get the signals needed up out of the noise.

3 With lots of stations at high power and different channel mixes I am quite sure there are lots of variations as to what is harmful and what can be ignored. IM that is not at the frequency you want should be able to be ignored.

4 The biggest problem is the big guess for loss from blocking line of sight. 10 db error here would be easy and make a completely different preamp viable. I suspect this would also be where the tvfool calculations are most in error too, though I have not seen anything that better matches my received signals.

In my situation I have approx 1/3 of my signals at 11 miles away and the other 2/3 are at mostly 40 to 50 miles. Also the calculator seems to worry about the overload at the tuner which for me is a non-issue due to the number of splitters I use to feed various devices. So I would only have problems from overload at the preamps which just doesn't seem to happen in any observable way. If I was to judge by the LG tuner I might have thought I was getting some overload that was wiping out some weak signals I should get, but once I got the Zenith and found virtually everything receivable just fine that the LG was missing that theory went out the window.

It is interesting that the Zenith gets me all the missing stations that are in the direction of the strong ones! LG does fine on at least 2 of the 3 I get in the opposite direction. So I assume this means the older tuner can't handle a mix of strong and weak signals nearly as well.

So far I have tested with my LG HD tuner and the Zenith converter box only. Next I will try out my Samsung 260F and see what works there. My new preamp will be going up on the mast soon as I get my new rotor, but with the two 20 db ones in series working I don't think that will do anything except improve my noise floor. There should be no more than around 4 db loss between my tower mount vs my current basement location.

OK. The key channel I want now (till Feb.) is 57.
It has 589 kw at 49 miles
Strongest channel is 11 miles away at 948 kw at channel 42

I estmate about 40 ft of RG 11 cable with preamps now at about half way pt in cable run.
I'm guessing the strong stations I lose 15 db from hills and more like 25 db for the distant station I want. Both are listed as "1 edge" in tvfool.

tvfool reports I would need to be at 42 ft for LOS to ch 42 and at 132 ft for ch 57.
My antenna is at 25 ft.

Signals are weaker in summer as they have to pass through a grove of trees.

My dual blakes need transformers and a combiner so that should be about a db loss.

Distribution losses I'd estmate at about 11 db for 3 2-way splitters.

Since you don't cover my current preamps figure I'd be using AP4700 or AP4800 Winegard units since they used to both work marginally for me but not as good as my new ones.

correction: Forgot to check the old analog stuff. So:
Strongest analog channel is channel 62 at 4497 KW and also 1 edge and 11 miles

Thanks Rick0725. That sounds really close to what I get here! Except my locals seem to work OK with the high gain preamp also, except when airplanes fly over. I may add a second antenna just for the locals and lower gain as you suggest.

My AP4800 lately has not been getting channel 57 but something happened in the last year. I'm thinking it might have been damaged by nearby lightning. It had been working pretty good: I normally got a nice picture fully watchable about 80% of the time at nights, but rarely during the day time.

My current new more expensive preamps seem to fix that and I am getting solid signals reading up in the Good range of the LG meter during days too. (with AP4800 when it was working I got typically bottom end of Normal on meter. Plus I am now pulling in stations I could never get before. Maybe these handle overload better as well as having lower noise specs.

Impressive results. Looking at the temporary mount on a fence has me concerned (a fence like that will reflect signals), but there is no substitute for results.

A couple years ago, I was convinced that OTA wouldn't work at my location. My first tests were with a Terk antenna in my computer room (A bad idea, with so much noise). Antennaweb almost steered me away again months later, but sometimes DTV can work wonders.

How do the analog UHF stations look on the 91XG?

The channel 27 Jointenna will reduce the signal strength of channel 27 by about 20 or so dB with negligible effect on your nearest lower (21) and higher (33) channels.

Preamplifier and tuner overloads have multiple deliterious characteristics that are nearly impossible to calculate in systems in which there are significant differences in signal levels but generally, when a preamp input is excessive, the degradation first becomes visible on the weaker channels, not the stronger ones.

If you have any problem with unamplified reception of the weaker channels and if you decide to go with the preamp, the Jontenna will do about as much for you as the Tin Lee product and costs only 1/3 as much. The advantage of the Tin Lee filters is that they are better shielded, which is important if you are near several transmiters, as most of my installations are, but that shielding is of negligible benefit in your situation.

Signals per tv fool are -41 dbm to -110 dbm

Tested tuners: Zenith converter DTT900, Samsung 260F LG 3410A
preamps none, Research Communications (9260), or Research Communications with kitztech (kt100VG).

11 channels with LG and no preamps
12 channels with Zenith Converter and no preamps

12 channels Samsung with 20 db (1 preamp)
14 channels Zenith with 20 db (1 preamp)

15 channels LG with 40 db (2 preamps)
19 channels Samsung with 40 db (2 preamps)
22 channels Zenith with 40 db (2 preamps)

Note: channel 13 VHF has it's own Channel Master preamp and was not varied, but Samsung could not receive it!

I assume I am not getting any overload issues even with 40 db gain due to getting more channnels with all tuners, and due to signal meters reading higher in all cases as I added gain for all channels or reading the same for some strong ones.

See previous posts for info on splitters, antennas, etc.
Preamps are still in my basement. The Research Communications unit will be going on my mast next.

Channel totals were not necessarily completely glitch free but were fully watchable. Did not count any with pictures that froze or blocked badly.

When I did get glitches it was often on the stronger stations too, but all cases the more preamp gain the less problems I had with glitches.

Finally I noticed that the Zenith converter could handle far wider antenna angle range than the other tuners for most channels.

I just went back and read a few earlier posts in this thread and will contribute the following

1. Winegard AP4800s actually have 36-38 dB gain between about 500 MHz and 530 MHz. A few years ago, someone reported observing that on his unit and so I bench-tested tested two of mine and found the same thing.

2. Manufacturers tend to use input signal level as their reference level for preamp overload, whereas most tend to use output level as their reference for distribution amplifier overload. FWIW, if you work the numbers backward, the Winegard 4800 and 4700 have the same maximum output.

3. Winegard briefly made an intermediate gain product it called AP4747 with 23 dB of gain. I bought a few of those. The slip of paper shipped with them is for the AP4700 and AP4800, and makes no mention of the AP4747. I even called Winegard up and asked about it, but the technician I spoke with couldn't find any references to such a product in his files. A few years ago, an AVSForums member working for a big company said they were a specialty product his firm had Winegard make up. I was never able to verify that, but it is as good an explanation as anything I can dream up myself. I assume that it uses the same power amplification component as does the AP4700 and AP4800.

Anyway, I compared the performance of two Winegard AP4747, 23 dB gain amplifiers with two Channel Master 0064DSB amplifiers with 23 dB of UHF gain. The Channel Master amplifier's published specs indicate that their overload point is about 10 dB LOWER than Winegard's published spec, but the Winegard's started visibly beating up a weak analog channel the antenna was receiving when the signal input and output signals were about ten dB LESS than the point at which the Channel Master unit began to cause those symptoms.

We don't know diddley about calculating the interference that strong signals will cause on weak signals in an overdriven amplifier. ChannelMaster used to define overload as the point at which 5% sync compression took place, but then one year, they instead defined it as the point at which -46dB of cross modulation was developed, in each case with a channel load of four identical strength channels. Coincidentally, the numerical overload figures they gave were exactly the same for excessive cross-mod as for excessive sync compression. Coincidence, or did the sales team simply acknowledge that more customers were asking for intermodulation specs and attempt to accommodate those customers by calling their sync compression limits the new cross-mod limits?

If you look at the published overload specs for high quality power amplifiers, they have several different ones published because cascades of amplifiers interact in different ways and can exceed one type of intermodulation threshold first in one configuration but exceed another first in another config.

It appears that the more responsible, mast-mounted preamp manufacturers are now furnishing as their published overload specs a level at which an amplifier carrying just one channel will develop some arbitrary reference benchmark of on-channel 3rd order IMD. From there, an engineer is supposed to work from that benchmark and figure out how it affects his system. Some rules of thumb I have been taught previously are: 1) that each time you double the number of equal strength channels, the maximum input or output level for that amplifier at which the benchmark 3rd Order IMD stays at that level goes down by 3dB, 2) that each time you double the number of fully driven amplifiers in a cascade (for home owners, that would typically be two amplifiers), your maximum input/output must go down by 6dB, and, 3) for each 1dB you lower the input/output, you reduce 3rd order IMd by 3 dB.

I have also read in a technical paper that when an amplifier develops -40dBc on its own digital channel, it develops 12 dB lower 3rd order IMd (-52 dBc) on its adjacent channels. I am in a market where my local 39 (temporary channel assignment) often exceeds desirable channel 38 and 40 by twenty or more dB, but while my receivers can accommodate adjacent channel signal differentials of 26 to 28dB, the intermodulation distortion caused by the strong channel 39 will exceed the maximum endurable levels for
processing of channels 38 and 40 before it exceeds the level it inflicts upon itself. I have a similar, vexing problem with temporary strong digital channel 51 and weak digital channel 52.

Cable TV engineers have it easy because all of their signals are at the same level and because their spectrum is fully loaded, so they are engineering to avoid one uniform, interference threshold level, but in the off-air antenna business, we don't have a clue how to figure out the nature and levels of the interference that our amplified spectrum throws on our weak channels. Fortunately for us, the ATSC waveform can take a licking and keep on ticking, but because everyone's situation is unique, it explains why people here encounter so many situations in which someone is certain that something will work for someone else that doesn't work for them, and vice versa.

I doesn't.


It is.


You aren't.

Thanks for the VHF preamp tip. For now I am happy since I get our channel 13 on the LG I use most (due to the hard disk) but after Feb we will have a bunch more VHF to get.
My current VHF preamp is a Channel Master with FM trap. I think I have a Blonder Tongue UV combiner.

My UHF preamps are right beside each other currently in my basement. Antenna line feeds into the Research Communications unit, then it's power supply. Then to the kitztech all in one box and to the line up to my tv.

There is maybe 2 ft of cabling between the boxes.

Been pondering a lot why this all works for me and others get great signals with just an antenna and no preamp when they are talking levels at -100 dbm that I have trouble getting with preamps. I think it all boils down to three things:

1 tvfool states that their resolution is somewhat limited. I can see from topo maps that I am fully blocked from Needham towers by a hill but tvfool says I have line of sight. This must mean my locals are weaker than specified.

2 I think due to error correction and the more evenly used spectrum on each channel that digital tv may be somewhat more tolerant of overload than analog in preamps.

3 I am in a bad multipath area and I suspect that equals somewhere about 20 to 25 db loss of usable sensitivity at my tuners, especially the older generation ones.
I think the Zenith performance is from this better multipath handling than any big sensitivity difference. It does seem to handle a mix of strong and weak signals better too, since it is the one that pulls in RI stations best, which are about in line with the locals in Needham MA.

A free downloadable .xls reader is available on the Microsoft website.

Regarding the rest of the commentary here, you people can buy old, analog field strength meters on eBay for typically $20 to 30, and you can buy old digital FSMs designed for analog only signal measurement for typically $100 to $200. You can get a pretty good approximation of your digital signal strength by adding 8dB to the readings they develop when used on a digital waveform.

Are there any you would recommend?

I'm considering using a Leader 941, which would probably be better than looking at the AGC reading on my TV, which is the closest I can get to a signal strength reading right now.

I often use a Leader 941 to measure digital signal strength. The nice thing about it is it only weighs a couple of pounds. The bad things about it are, 1) it uses C cells rather than internal rechargeable batteries, 2) it only reads to whole dB, and, 3) you can't select exact frequencies: you can only select the aural and visiual carrier frequencies used in the cable standard and broadcast off-air channel plans.

Both UHF and VHF show improvement for increased antenna height, though for different reasons at times.

If analog 7 is strong in the bedroom, you can probably have it on the bottom of the stack. This seems to be the most popular configuration for a separate UHF/VHF stack (UHF on top and VHF on bottom).

KTBC-DT 7 will be relatively strong at 30kW, but I see their Construction Permit is for a directional antenna. The coverage for Llano appears to be comparable from the service area contour, however.

http://www.fcc.gov/fcc-bin/FMTV-serv...DT1238906.html

Per their DTV transition report filing, KNVA wants to use the current facility as the post-transition facility:

http://fjallfoss.fcc.gov/prod/cdbs/f...ibit_id=618114

Hopefully, they will file for an increase in ERP when the contour freeze is lifted in August. Continuing to use the existing Non-Directional antenna is probably the main objective and not the directional antenna proposed by the allotment table. Perhaps you can write them and ask for more power.

Other than that, I'm glad it's working well. It's always nice to hear success stories.

KNVA has filed a maximized application for 49, so perhaps they aren't completely pleased with 197kW after all. If granted, the ERP would be increased to 500kW.

http://fjallfoss.fcc.gov/prod/cdbs/f...ibit_id=645616
http://fjallfoss.fcc.gov/cgi-bin/ws....01&fac_num=144

Hopefully, this would be enough to make it reliable.

jhe,
I,m here in Burlington, MA trying to get WLNE and WJAR (from Providence)
reliably with my newly installed CM 7777. What I'm experiencing is a total wipe-out
of all channels, including the close Boston channels (11 miles) in the Needham area.
The strong Boston channels are directly in line with the Providence antenna farm, in
Rehobeth, MA. Is it really possible that the loss of all channels is attributable to the
overdriving of the 7777 pre-amp? Since I'm a newbie to OTA I know I would benefit
greatly from any remarks you may make about your related experiences.

Thank You, GR

NOTE: Grigor Rasputin is not the thread starter, but his problem is similar, so he has posted at the end of this old thread. He is talking to jhe in post #45 above who is in Lexington, MA.

I think you should have started your own thread GR, but maybe this will work. Don't be surprised if admin separates your post out to a new thread.

GR:

Welcome to the Forum. Your tvfool report for Burlington looks like this:
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id%3d1349de0acca553

A tvfool report with your exact address would be more accurate, but you probably can't post an active link yet. You can, however, give us the URL in bold type near the top of the report and we can post it. Yes, quite likely. It is also possible that your tuner is overloaded.
There are preamps that can tolerate higher signals levels than the 7777, but you still need to be concerned about the tuner. That makes it a very difficult problem to solve, because your local signals are about 35 to 40 dB stronger and in the same direction.

Don't get your hopes up, but one possible idea would be to insert an attenuator between the antenna and the input of the preamp. Adjust the value of the attenuator (perhaps 10 to 15 dB) to eliminate the overload, but still retain sufficient gain to help you with the Providence signals. You could also try an attenuator between the output of the CM power supply and the TV. The best location for an attenuator would depend upon which is being overloaded first, the preamp or the tuner. Without even adding the antenna gain, your strongest signal (WMFP at -24.2 dBm) plus the preamp gain, puts you at the overload point of the tuner.

ATSC Recommended Practice:
Receiver Performance Guidelines
Document A/74:2010, 7 April 2010

5 RECEIVER PERFORMANCE GUIDELINES
5.1 Sensitivity
After you got through messing with attenuators, the results probably would not be as good a just removing the preamp, which would be a lot easier. There is an expensive solution which involves separate antennas, two preamps, custom bandpass filters for CH49 and CH51, and A/B switches.

What antenna are you using, and where is it located?
Edited by rabbit73 - 6/23/12 at 9:09pm