How to build a UHF antenna... - Page 71 - AVS Forum
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post #2101 of 4798 Old 03-16-2009, 04:18 PM
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Quote:
Originally Posted by 300ohm View Post

Dont really know until more smart antennas come out. Most smart antenna designs to date involve phase shifting to change the direction of the antenna. That really doesnt work out too well with bowties or other higher gain antennas. So look for most smart antennas to be local area antennas, at least in the immediate future.

NONE of the DTV Smart Antenna patents I've read work via phase shifting,
although that is a very viable technique for Adaptive Antenna Arrays (AAA).

Most of the patent disclosures describe forming a beam towards 16 compass
headings by summing the output of (say) the North and East antennas
with equal Preamp gain weighting to receive from NE and 3/4 N + 1/4 E to
receive from NNE, etc.....it's not optimal, but it's fairly low cost...

In Europe they use multiple tuners with Maximal Ratio Combiner (MRC) software
in dual and quad diversity DVB-T receivers (currently available for cars & buses).
MRC is a far superior technique, working in concert with the adaptive equalizer
to coherently sum ALL of the multipath components on ALL of the antenna inputs,
irrespective of phase relationships...but it has yet to get out of the lab for ATSC.

More info re "Maximal Ratio Combiners":
http://www.avsforum.com/avs-vb/showt...php?p=13015675
http://www.avsforum.com/avs-vb/showthread.php?p=5842783

BTW: There are 100's (1000's?) of papers and PhD theses re EQUALIZATION and
dozens (100's?) re MRC and other combining techniques, but very few re joint
optimization of the collective processes...anyone looking for a PhD research topic????
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post #2102 of 4798 Old 03-16-2009, 05:59 PM
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Quote:


NONE of the DTV Smart Antenna patents I've read work via phase shifting,
although that is a very viable technique for Adaptive Antenna Arrays (AAA).

Yeah, I havent read any of the Smart Antenna patents, because Im sure most will go to the wayside, heh. Im just waiting for the smoke to clear on it to do some serious investigating, heh. I was just going by some articles I have scanned over.

Quote:


Most of the patent disclosures describe forming a beam towards 16 compass
headings by summing the output of (say) the North and East antennas
with equal Preamp gain weighting to receive from NE and 3/4 N + 1/4 E to
receive from NNE, etc.....it's not optimal, but it's fairly low cost...

That in my crude way was what I was meaning to convey to sustorm, even though I know what you mean by that technique for Adaptive Antenna Arrays (AAA).
Quote:


anyone looking for a PhD research topic????

YODA: He is too old. Yes, too old to begin the training.

Quote:


In Europe they use multiple tuners with Maximal Ratio Combiner (MRC) software
in dual and quad diversity DVB-T receivers (currently available for cars & buses).
MRC is a far superior technique, working in concert with the adaptive equalizer
to coherently sum ALL of the multipath components on ALL of the antenna inputs,
irrespective of phase relationships...but it has yet to get out of the lab for ATSC.

Yep, the ole brute force method. Multiple antennas, multiple downleads into multiple tuners and a logic circuit to pick out the best signal.

BTW, did you see that LDPA UHF antenna from the past on that other site ? I bumped it up to the first page for you.
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post #2103 of 4798 Old 03-16-2009, 06:33 PM
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I spoke to a guy earlier today that has a never used ChannelMaster 4228. Since it has the 8" bowties it will not be as effective as mcclaps design but I am willing to buy it if the price is right. I have seen the HD version of the
4228 running around $80 with shipping.

I have just started reading the postings on this forum and I am at page 10 and very impressed. I plan on building one of the mcclapp 4 bay bowties and will testing it with a spectrum analyzer - I will do the same for the ChannelMaster 4228 with a spectrum analyzer if I buy it.
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post #2104 of 4798 Old 03-17-2009, 09:53 AM
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What is the fair market value for a New in box ChannelMaster 4228 (Old style)?

I would say to look on ebay for the prices.
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post #2105 of 4798 Old 03-17-2009, 05:42 PM
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I got a Insignia NS-DXA1-APT Digital to Analog Converter Box coming in the mail from ebay..I'm going to make a good UHF Antanna for it
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post #2106 of 4798 Old 03-17-2009, 05:59 PM
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Yeah, its a good unit, I have an Insignia too. Its the exact same unit as the Zenith.

I also have a Zenith, a Sansonic, a Apex and an AccessHD. They all have their unique features. The AccessHD is the crappiest of the lot, but still works reasonably well.
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post #2107 of 4798 Old 03-17-2009, 07:28 PM
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Quote:
Originally Posted by wm_tell1 View Post

I spoke to a guy earlier today that has a never used ChannelMaster 4228. Since it has the 8" bowties it will not be as effective as mcclaps design but I am willing to buy it if the price is right. I have seen the HD version of the
4228 running around $80 with shipping.

I have just started reading the postings on this forum and I am at page 10 and very impressed. I plan on building one of the mcclapp 4 bay bowties and will testing it with a spectrum analyzer - I will do the same for the ChannelMaster 4228 with a spectrum analyzer if I buy it.


Welcome to the forum,

What is a 4228 worth? I know they used to sell for about $50 - $60 at one time. Just like anything, what's it worth to you?

Looking forward to your spectrum analyzer tests, I did some last fall and it was very educational.
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post #2108 of 4798 Old 03-18-2009, 08:50 AM
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So I built my mclapp 9x8.5 with bottle cap standoffs. It looks like a monster, lol. my measurements were correct but I forgot to factor in the diameters of the phase lines and whiskers, so the separation of my phase lines are about 3/4 to 1 inch apart not 1 3/8's. I have not placed it where my current antenna is but in the window of my apartment it out performed my current antenna in the same window. I will take some pictures and get it in the attic tomorrow morning and I will post the results.
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post #2109 of 4798 Old 03-19-2009, 08:30 AM
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Sorry no pictures today, my camera battery is dead. I put my mclapp up in my attic with mixed results, my LP analog station(ch 20) came in about 10-15% stronger without static, snow or ghosting but I lost 1 digital channel WNYS(44)(Syracuse, North) and lost about 5-10% signal quality on WSYT(19)(Syracuse).

I was not able to gain WBRE(11), WYOU(13), or WQPX(32) out of Scranton(South) or WETM(2) out of Elmira

Can this be due to incorrect phase line spacing about 1/2 inch too close?
Would a picture help to review my mistakes?

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post #2110 of 4798 Old 03-19-2009, 09:02 AM
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Would a picture help to review my mistakes?

Certainly cant hurt.
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post #2111 of 4798 Old 03-19-2009, 09:06 AM
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The mclapp's perform much better when built to spec. IMO, you will see a significant improvement if you rebuild and make the phase lines have the correct and consistent spacing throughout. I saw improvement on my second build, correcting errors in the first... As I understand it, too wide of phase lines results in tuning the antenna lower. Too narrow may tune it higher??? Are you using a reflector? I saw a nice boost with a reflector (+3 to 4 dB increase in margin to dropout). Good luck! I'm very impressed that you can receive Fox, ch 19!
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post #2112 of 4798 Old 03-19-2009, 10:09 AM
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Quote:
Originally Posted by sustorm View Post

So I built my mclapp 9x8.5 with bottle cap standoffs. It looks like a monster, lol. my measurements were correct but I forgot to factor in the diameters of the phase lines and whiskers, so the separation of my phase lines are about 3/4 to 1 inch apart not 1 3/8's. I have not placed it where my current antenna is but in the window of my apartment it out performed my current antenna in the same window. I will take some pictures and get it in the attic tomorrow morning and I will post the results.

It may help to make the phase lines further apart but I'm not sue how much. If it's not too hard to do give the wider spacing a try.

A reflector will give more gain but you will lose the dual direction receive capabilites which may be OK depending on what stations you want. Even with a reflector you should still get the binghamton stations no matter which way you point except for maybe ch34 (real ch4).

That antenna is pretty much worthless below ch7 so not much chance of getting 18.1 coming in on real ch 2. You may want to try the analog signal on ch18 to see what your chances are after the switch.

According to your TVFool plot getting the Scranton stations with that antenna mounted indoors will be tough. It's hard to say how accurate that plot is since it shows 19 and 44 as being quite weak, especially for indoors, but you are able to receive them.

As you can see antenna placement is real critical when dealing with the more marginal signals, finding the hot spot may be more worth you time than rebuilding the antenna or adding a reflector of course both would be best.
Have Fun!!
Mike
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post #2113 of 4798 Old 03-19-2009, 11:56 AM
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Any help in locating the hot spot? I have access to 1/3 of my attic due to cathedral ceilings and vent/exhaust piping. The attic is standard trusses and the antenna is located as high as possible in between two trusses in the middle of the available space.

The whiskers are about 1/8-1/4inch away from the trusses and the top whisker is about the same distance away from the wood roof. I attached the antenna via an eye hook into the roof and an eye hook into the 2x4 portion of the antenna with a link in between. That makes for easy adjustment.

Should I move the antenna lower so there is more air space at ends of the whiskers? Any other suggestions?
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post #2114 of 4798 Old 03-19-2009, 12:51 PM
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Quote:
Originally Posted by sustorm View Post

Any help in locating the hot spot? I have access to 1/3 of my attic due to cathedral ceilings and vent/exhaust piping. The attic is standard trusses and the antenna is located as high as possible in between two trusses in the middle of the available space.

The whiskers are about 1/8-1/4inch away from the trusses and the top whisker is about the same distance away from the wood roof. I attached the antenna via an eye hook into the roof and an eye hook into the 2x4 portion of the antenna with a link in between. That makes for easy adjustment.

Should I move the antenna lower so there is more air space at ends of the whiskers? Any other suggestions?

height isn't always the most important.

in an attic you may have reflections from the dwelling giving both constructive and destructive interference.

also there can be reflections from the earth outside your house giving both constructive and destructive interference.

you just might have to move around in all dimensions to find a spot. if you you still have analog stations from the same tower you could use that for faster initial aiming (there is a good reason for that delay, more time for antenna work).
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post #2115 of 4798 Old 03-19-2009, 01:01 PM
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It's hard to justify the complexity and cost of the 'smart antenna' technology for home TV. The simple and cheap passive antennas work so well, especially with the narrowed post-transition frequency range. I expect it to be a commercial novelty, useful in a few places where desired signals come from different directions, until it is further developed to the extent that it can solve the multipath problems. At that time, the ideal antenna will be a ring of J-poles with the adaptive electronics actually at the antenna. Make it fast enough, and it could be a boon to mobile TV reception. Actually, they wouldn't even bother with J-poles, but would instead use simpler base-fed verticals, and design the electronics for whatever impedance results from simple construction. Then, TV broadcasters will migrate toward circular polarization, perhaps eventually vertical polarization. Take that as my prediction, though I may not live long enough to see it fulfilled.
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post #2116 of 4798 Old 03-20-2009, 01:27 AM
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Currently, Smart Antennas cost about $100. Many people have invested a lot more than that
in multiple antennas and even $100-200 low loss stripline couplers....usually because
signals come from multiple directions and a rotator is not a viable option....

Some TV broadcasters are already going to elliptical or circular polarization, esp those
stations moving DTV to their old VHF channel, since they likely needed to buy new antennas.
The reason??? Vertical polarization to Mobile DTV in cars, buses, trains and afoot.
BTW: Mobile DTV is using the newly approved ATSC-M/H modulation modifications...

FCC database shows ten out of 22 DTV stations in S.F. are elliptical or circular polarization:
http://www.rabbitears.info/ss/
As Mobile DTV becomes more popular, more stations are likely to add polarization.
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post #2117 of 4798 Old 03-20-2009, 05:19 AM
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The reason??? Vertical polarization to Mobile DTV in cars, buses, trains and afoot.

Also circular polarization is a godsend to people in large cities with large buildings around them.

Hmm, Ill have to see what the DBGH pattern and gain will look like if stacked one SBGH vertical and the other horizontal. It may actually work, if I get the phasing lines bent in a way that they are still equal.
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post #2118 of 4798 Old 03-21-2009, 09:55 AM
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Quote:
Originally Posted by fdimegli View Post

snash22,

I guess you really mean antennas at 223 True not 229 (looking at your TVFOOL plot.) But the 4-bay beamwidth should get the neighboring channels too.

Your channels are lower end UHF and some Upper VHF (11, 13.) You won't get VHF channel 3 with this 4-bay without a miracle. If you need 3 then use a lower VHF antenna and either combine them or switch them (search thread for combining ideas.)

For your target set of channels you probably need a 10.5x10 or a 10x9.5 4-bay most likely with a reflector mounted behind it. Many reflector plans are in the thread; I cannot give you an opinion as I don't use a reflector - perhaps someone else will chime in. Either of these dimensions should get you true channel 17 and channels 11 and 13.

Since you want to attic mount, the reflector could be an aluminum foil covered cardboard of the correct dimmension mounted 4" behind the 4-bay (15" behind improves VHF but slightly depresses UHF.)

fdimegli - You rock!

I made the 10x9.5 as close as I could get to the mclapp specs (mclapp rocks too), no contact with wood. My reflector is a kludge right now using aluminum foil hung on chicken wire, varying from 1 to 5 inches from the elements. I am getting all the channels I wanted including the the grail - WFXR.

Most of the channels are 60 miles away, from my attic. All are UHF. Path is 2EDGE.
LL
LL
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post #2119 of 4798 Old 03-22-2009, 10:52 AM
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I had to chance to test my version 2 mclapp Friday. The mclapp is a 10x9.5 4-bay with a 36" x 36" angled reflector (4 inch spacing). The mount height was ~20 ft AGL (or 5 ft above the roof line when measured at top of antenna). Our locals are broadcast from two different directions (199 and 270 degrees). Current tvfool results are here: http://www.tvfool.com/?option=com_wr...d%3df358f0f862 I evaluated five different aiming directions (200, 217, 235, 252, and 270 degrees). Results are illustrated in the attached graph.

Summary:

Aiming direction had minimal effect on SS % with real channels 9 and 17. Ch 23 is stable from 200 to 235 degrees but drops off as antenna is aimed further west. Ch 31 and 36 were the most affected by aiming direction. SS's are peaked for these two channels between 217 and 235 degrees.

Questions,

Will a curved reflector increase signal strength on ch 31 and 36?

What is the beam width with a curved reflector versus angled reflector?

Are beam widths similar between the mclapp 4-bays and the SBGH's?
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post #2120 of 4798 Old 03-22-2009, 08:09 PM
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I wanted to give just a bit more information on my situation. At 217 degrees, my lowest signal strength channel (ch 36) has a margin to dropout of approximately 20 dB. At 235 degrees, the margin to dropout for the lowest station decreases to 16 dB. All SS measurements were made with an Apex DT502 and a fixed cable length of 25 ft. Margin to dropout was estimated from previous test data.

Switching to a curved reflector may improve signal strengths when aiming directly at the towers. However, it may also reduce beam width and reduce my margin to dropout at the compromise point. I do not want to use two antennas nor do I want to use a rotor. My goal is to find the best aiming solution with a single antenna. Going higher may help but that is not practical as I need to be at the north edge of the roof for best LOS to both sets of towers. Guying the antenna is not practical at this location.
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post #2121 of 4798 Old 03-22-2009, 10:10 PM
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However, it may also reduce beam width and reduce my margin to dropout at the compromise point. I do not want to use two antennas nor do I want to use a rotor. My goal is to find the best aiming solution with a single antenna.

Yep, thats why high gain isnt always the best solution. Generally, the higher the gain, the narrower the beam width of the pattern.
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post #2122 of 4798 Old 03-23-2009, 09:38 AM
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IDRick,
The swept forward elements and curved or angled reflector does narrow the beamwidth and adds about 2db forward gain on UHF. If you went iwith a flat element and flat reflector you would lose that 2db in the center but may gain more than that on the edges of the beam due to the fact that the beam doesn't fall off as sharply.

The difference between the curved and angled reflector as far as gain and beam with goes varies from channel. The difference only 1-2 db here or there and the beamwidth is only a couple of degrees, the main difference is the curved reflector is more consistant in gain and beamwidth across the UHF band.
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post #2123 of 4798 Old 03-23-2009, 10:11 AM
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Quote:
Originally Posted by sustorm View Post

Any help in locating the hot spot? I have access to 1/3 of my attic due to cathedral ceilings and vent/exhaust piping. The attic is standard trusses and the antenna is located as high as possible in between two trusses in the middle of the available space.

The whiskers are about 1/8-1/4inch away from the trusses and the top whisker is about the same distance away from the wood roof. I attached the antenna via an eye hook into the roof and an eye hook into the 2x4 portion of the antenna with a link in between. That makes for easy adjustment.

Should I move the antenna lower so there is more air space at ends of the whiskers? Any other suggestions?

The best help in finding the "hot spot" for your antenna is to use what IDRick, 300ohm and I are using: the Apex DT502 (NOT the 250---my local BestBuy has them stacked together) CECB. The Apex has two signal bars, one for signal QUALITY and one for signal STRENGTH. Use the signal strength bar first to find the best location for the strongest signal and then use the signal quality bar to optimize the antenna aim which will be when the BER is lowest to minimize dropouts.

Of all the boxes with two signal bars that I have tested, the DT502 gives the most consistent results, but the remote control isn't much to brag about and the percent font is harder to read than on the Sansonic.

The Apex signal strength bar will max out in the 80s with the strong signals in green (which would require an inexpensive attenuator between the antenna and the CECB to see changes in strength), but it should help you with the weak signals in gray; it's even more sensitive than a SLM (signal level meter):
http://www.avsforum.com/avs-vb/showt...6#post15414426 post #8424

If you can not measure it, you can not improve it.
Lord Kelvin, 1883
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post #2124 of 4798 Old 03-23-2009, 10:26 AM
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The best help in finding the "hot spot" for your antenna is to use what IDRick and I are using: the Apex DT502 CECB.

Hey, dont forget me. Im also using it and the Sansonic FT300a, heh.

The Sansonic has the advantage of using a wall wart (5 vdc, 1.4A), so it can be later hooked up to a battery for portable use.
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post #2125 of 4798 Old 03-23-2009, 10:28 AM
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thanks Rabbit!
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post #2126 of 4798 Old 03-23-2009, 10:30 AM
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300ohm:
Sorry, I'll edit my post.

I use an inverter (Exeltech XP125) with a 12V jumper battery pack to power my Apex box and the LCD monitor when no outlet is available.

If you can not measure it, you can not improve it.
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post #2127 of 4798 Old 03-23-2009, 11:50 AM
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Quote:
Originally Posted by mclapp View Post

IDRick,
The swept forward elements and curved or angled reflector does narrow the beamwidth and adds about 2db forward gain on UHF. If you went iwith a flat element and flat reflector you would lose that 2db in the center but may gain more than that on the edges of the beam due to the fact that the beam doesn't fall off as sharply.

The difference between the curved and angled reflector as far as gain and beam with goes varies from channel. The difference only 1-2 db here or there and the beamwidth is only a couple of degrees, the main difference is the curved reflector is more consistant in gain and beamwidth across the UHF band.

Thanks mclapp! I'll give it a try with a flat reflector. Personally, I was surprised at the linearity in signal strength for individual stations. I would have guessed a curvilinear response, breaking sharply after 30 degrees off center. This will give me a chance to try my hand with pvc components...

Best,

Rick
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post #2128 of 4798 Old 03-23-2009, 01:38 PM
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Years ago back when there were not that many stations on the air & most were VHF, some folks used single channel antennas when the channels were in different directions to avoid using a roter. Also it was like having TV cable because you could instantly change to any of the channels & not need to wait for the rotor to turn the antenna to each station.

I would like to try the same thing except the channels now are UHF. But some of the channesl now are in the same direction & some are not. Instead of like having 4 single channel antennas pointing in the same direction I am planning to build a uhf yagi antenna with only the dipoles for the channels that antenna is to receive. I think I should be able to put the diplole cut for the lowest channel on the back ch29 next ch30 then ch44 & ch46. I do understand the formula for the length of the dipole; But I am unsure of the spacing between each dipole. If they are placed right, the dipole for ch29 would act like a reflector for the signal on the ch 30 dipole. Also the ch 44 dipole would be a director for the signal to the ch 30 dipole. From the what I understand the VHF low band, VHF high band & UHF yagi antennas was set up like this. Except the diffence it I am skipping a lot ot channels where the manuf antennas covered the channels as a group.

Does any one care to brain storm with me on such a project.

Thanks in advance
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post #2129 of 4798 Old 03-23-2009, 08:50 PM
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Sorry, I'll edit my post.

Heh, thats better. Your comparison analysis with the Apex was very useful, thanks again. Deep down, I always thought these cheap CECBs could be sensitive, down and dirty tools to use. I also use the kiddie Mattel/Intel digital microscope because it serves my practical needs pretty well, heh.
IIRC, you also have the Sansonic. Can we expect another comparison analysis soon, heh ? (no pressure)

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use an inverter (Exeltech XP125) with a 12V jumper battery pack to power my Apex box and the LCD monitor when no outlet is available

Yeah, but with the Sansonic, you could just slap together 4 NiMH (1.25v X 4) batteries and have a small portable unit, very important when dealing with working in high places.
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post #2130 of 4798 Old 03-24-2009, 11:01 AM
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Originally Posted by 300ohm View Post

Your comparison analysis with the Apex was very useful, thanks again. Deep down, I always thought these cheap CECBs could be sensitive, down and dirty tools to use.

That was my goal, to find an inexpensive measurement tool that the average guy could use when he was having reception problems.
Quote:


IIRC, you also have the Sansonic. Can we expect another comparison analysis soon, heh ? (no pressure)

Maybe after I finish with my tax forms.
Quote:


Yeah, but with the Sansonic, you could just slap together 4 NiMH (1.25v X 4) batteries and have a small portable unit, very important when dealing with working in high places.

That's the way itsthemultipath! uses his Sansonic, but he has found that the box acts up when the battery voltage drops. I'm wondering how critical the voltage tolerance is. I asked Sansonic, but didn't get a satisfactory answer.

Even if you run the box on 4 NiMHs, how do you power the monitor to check the picture quality?

If you can not measure it, you can not improve it.
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