Weiser, ID: Truck interference, re-purposing dish-mounted Terk - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 34 Old 01-17-2017, 05:04 PM - Thread Starter
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Weiser, ID: Truck interference, re-purposing dish-mounted Terk

I live on a road that's a truck route and every time a semi-truck rolls by, I get interference with my ATSC TV reception. Audio dropouts, stuttering and blocky picture.

Diesel engines don't have an ignition system to emit RF to cause havoc with TV, so what's doing it? Is there anything that can be done to block or shield a TV antenna from that interference?

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post #2 of 34 Old 01-17-2017, 07:13 PM
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It's unlikely that the trucks are emitting electrical interference.

The trucks are like giant moving mirrors to the signals as they roll by. The signal is either being block by or reflected off of the trucks as they pass. Your primary signal path is probably poor so the strength of the unwanted signal is sufficient to cause signal dropouts.

Your best measure is to get your antenna as ideally situated as you can so that it simultaneously gets its strongest desired signals while simultaneously avoiding the effect of the trucks' passing.
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post #3 of 34 Old 01-17-2017, 07:42 PM - Thread Starter
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The antenna I have is atop a building about 20 feet up in the air. It's the smaller version of the TERK loop that was so common on Dish and DirecTV satellite dishes. Going to be replaced soon with a Mohu Sky 60.

At any rate, with the height, it can't be the trucks blocking the signal.
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post #4 of 34 Old 01-18-2017, 02:33 AM
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It's probably Multipath Reflections, which is made WORSE by the Doppler Shifts due to Truck Speed....ATSC Waveform was never designed for simple Doppler Offsets....and DIFFERENTIAL Doppler between Direct and Multipath Paths, which is even MORE difficult to correct for. BTW: DVB-T and ATSC 3.0 are designed to have high resistance to this kind of interference.

But I also wouldn't overlook the possibility that at least SOME Trucks are Refrigerated, with a [probably 4-Stroke] Gas Engine built into the Trailer. But I doubt that more than a FEW exceed FCC Emissions Requirements....so unlikely a source of your problem...shouldn't be any worse than cars and motorcycles.

Another possible source of EMI are the multiple Ground Straps dangling down from the Truck and each Trailer [making intermittent sparks as they bounce around], discharging Static Electricity to the Earth, which is generated by the Rotating Wheels.

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post #5 of 34 Old 01-18-2017, 03:40 AM
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Okay, at 20', it's presumably above the trucks as they pass. However, we don't know anything about your primary signal path and the path of the trucks relative to the signal path. Also, you've got a crappy antenna soon to be replaced by another crappy one that's not going to have any ability to fix your reception problem.

We'd really be able to help you if you provide specifics about your situation, specifics about the stations involved, your TVFool plot, and specifics about your setup. Otherwise, we can only waste time with generalities.
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post #6 of 34 Old 01-18-2017, 06:56 AM
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You're probably experiencing something similar to airplane induced multipath. Here's an animation of a weak DTV signal. The signal takes on the appearance of a sine wave when an airplane gets in between the transmitter and the receiver.

http://images.aa6g.org/AVSForums/KGO-Animation-3.gif

This happens when you don't have line-of-sight to the transmitter and the reflection is strong relative to the main signal. You might benefit from a larger more directive antenna that could better reject the reflections. As mentioned, a link to your TV Fool report would be helpful along with a detailed description of your antenna setup.
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post #7 of 34 Old 01-18-2017, 08:37 AM
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his previous post with a little more information:

DirecTV mount pipe inside diameter?
https://www.avsforum.com/forum/36-hom...-diameter.html

My antenna is only 5 feet AGL and aimed across a well-traveled road. The strong signals are OK, but the very weak ones break up when a truck passes by. I tried raising the antenna higher, but it got worse because the reflections were out of phase with the direct signal.

The first thing you need to do is use an antenna with a narrow vertical acceptance angle. If that isn't enough, then you will need to shield the antenna from the signals reflected off the vehicles.

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post #8 of 34 Old 01-18-2017, 12:00 PM
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Quote:
Originally Posted by bizzybody View Post
The antenna I have is ... the smaller version of the TERK loop that was so common on Dish and DirecTV satellite dishes. Going to be replaced soon with a Mohu Sky 60.

At any rate, with the height, it can't be the trucks blocking the signal.
Agreed - the trucks aren't blocking the signal; they are reflecting it. I agree with holl_ands; this sounds like multipath.

I used to have that type of antenna. It doesn't have a lot of directivity (aka gain). It will receive signals from just about any direction, including above (aircraft) and below (trucks).

Unfortunately the Mohu Sky 60 isn't going to be much better. You'll probably have a lot better luck with a traditional Yagi or 4- or 8-bay panel antenna.
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post #9 of 34 Old 01-18-2017, 02:01 PM
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Quote:
Originally Posted by Calaveras View Post
You're probably experiencing something similar to airplane induced multipath. Here's an animation of a weak DTV signal. The signal takes on the appearance of a sine wave when an airplane gets in between the transmitter and the receiver.

http://images.aa6g.org/AVSForums/KGO-Animation-3.gif

This happens when you don't have line-of-sight to the transmitter and the reflection is strong relative to the main signal. You might benefit from a larger more directive antenna that could better reject the reflections. As mentioned, a link to your TV Fool report would be helpful along with a detailed description of your antenna setup.
I see the "sine wave shape" in the Spectrum Analyzer Display, but I'm going to GUESS it takes that shape during Airplane Multipath due to Constructive and Destructive Interference between the two Multipath Components, which varies across the Frequency Band....the Inverse of the Frequency Spacing [in nanoseconds], should be able to tell us something about the Path Differential [in FEET, since speed of light is about 1 ns per foot]....it varies with time....I see 2000 and 5000 feet.

Since Doppler Offsets would be SMALL [On-Line Calc found 31.6 Hz for 177 MHz at 60 mph], I don't think anyone can see THAT in the Spectrum Analyzer Display.

BTW: Signal below KGO on Ch7 appears to be an FM Audio Carrier on Analog Ch6 that is only infrequently coming in. Search of your zipcode within 130-km using fccinfo.com revealed only ONE Ch6 station: K06QM, which only shows it as being DTV....so perhaps the Video Capture was done on a ANALOG signal, prior to Digital Changeover???

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post #10 of 34 Old 01-18-2017, 04:56 PM
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Quote:
Originally Posted by holl_ands View Post
BTW: Signal below KGO on Ch7 appears to be an FM Audio Carrier on Analog Ch6 that is only infrequently coming in. Search of your zipcode within 130-km using fccinfo.com revealed only ONE Ch6 station: K06QM, which only shows it as being DTV....so perhaps the Video Capture was done on a ANALOG signal, prior to Digital Changeover???

Channel 6 is nowhere near channel 7 in frequency. Those signals popping up are public service transmitters.
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post #11 of 34 Old 01-18-2017, 07:12 PM - Thread Starter
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TVfool http://www.tvfool.com/?option=com_wr...e6a4d17f488365

http://www.tvfool.com/?option=com_wr...e6a4d17f488365

It's been snowing here since noon. Snowpocalypse 2017, breaking records and buildings since a couple of weeks ago. Got the roofs cleaned off just in time for more of this four letter word crap to cover them again.

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post #12 of 34 Old 01-19-2017, 07:21 AM
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Quote:
Originally Posted by holl_ands View Post
I see the "sine wave shape" in the Spectrum Analyzer Display, but I'm going to GUESS it takes that shape during Airplane Multipath due to Constructive and Destructive Interference between the two Multipath Components, which varies across the Frequency Band....the Inverse of the Frequency Spacing [in nanoseconds], should be able to tell us something about the Path Differential [in FEET, since speed of light is about 1 ns per foot]....it varies with time....I see 2000 and 5000 feet.

Since Doppler Offsets would be SMALL [On-Line Calc found 31.6 Hz for 177 MHz at 60 mph], I don't think anyone can see THAT in the Spectrum Analyzer Display.

Sorry that this appeared as though I was saying reflections off a passing truck and airplane multipath would look the same on the spectrum analyzer. Certainly that's not the case. It was only an illustration how signals can add/subtract when a reflection is involved.
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post #13 of 34 Old 01-19-2017, 07:31 AM
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Quote:
Originally Posted by bizzybody View Post
The antenna I have is atop a building about 20 feet up in the air. It's the smaller version of the TERK loop that was so common on Dish and DirecTV satellite dishes. Going to be replaced soon with a Mohu Sky 60.

At any rate, with the height, it can't be the trucks blocking the signal.
Quote:
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It's been snowing here since noon. Snowpocalypse 2017, breaking records and buildings since a couple of weeks ago. Got the roofs cleaned off just in time for more of this four letter word crap to cover them again.

Your stations are 55 miles and 1 edge. Your antenna is too small. I would not recommend anything less than a Winegard HD7698P.

Where is this highway in relation to the stations? Same direction? Off to the side somewhere? A better antenna could help a lot depending on where the trucks are.
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post #14 of 34 Old 01-19-2017, 09:22 PM - Thread Starter
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The road is right in front of my place, between the antenna and the transmitters.
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post #15 of 34 Old 01-20-2017, 04:06 AM
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The road is right in front of my place, between the antenna and the transmitters.
Then you need to mount the recommended antenna in the already recommended location and then, by having followed directions, your odds of reliable reception will be dramatically improved.
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post #16 of 34 Old 01-29-2017, 09:09 AM
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I used to live near a small air strip. In the days of analogue TV you could see the multipath reflections of the planes appear as 'ghosts' as the planes came in to land or took off. (This is just how RADAR works really)

Since we moved to DVB-T (and now T2) in the UK this hasn't been an issue at that location with the same aerial pointed at the same transmitter - clean pictures all the time. (DVB-T/T2 is COFDM-based, as I believe will ATSC 3.0 be. COFDM usually has far greater resilience to multipath - in fact reflections can be a benefit in some edge cases!)
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post #17 of 34 Old 01-29-2017, 03:09 PM - Thread Starter
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I used to live near a small air strip. In the days of analogue TV you could see the multipath reflections of the planes appear as 'ghosts' as the planes came in to land or took off. (This is just how RADAR works really)

Since we moved to DVB-T (and now T2) in the UK this hasn't been an issue at that location with the same aerial pointed at the same transmitter - clean pictures all the time. (DVB-T/T2 is COFDM-based, as I believe will ATSC 3.0 be. COFDM usually has far greater resilience to multipath - in fact reflections can be a benefit in some edge cases!)
Sort of like a passive radar.
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post #18 of 34 Old 02-01-2017, 01:44 AM - Thread Starter
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Got the Mohu Sky 60 installed, and yep, it's not as good as the old TERK DBS dish mount one. I had to try it, being a Christmas gift. It can get all the stations except for 22 and 35. No matter which way it's turned, nada on those two.
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post #19 of 34 Old 02-01-2017, 01:52 AM - Thread Starter
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Ontario, ID: Truck interference, re-purposing dish-mounted Terk

Can a normal TV antenna be connected, through a DC blocker, to an input on one of those TERK loop antennas that mount on a DBS dish? I know those TERK antennas can be used without a DBS box by using a power injector.

Or is the TERK input special in some way where it only works with DBS feedhorns? It has to pass power through as well as tapping the DC for its own amplifier.

Has anyone tried straightening out the curve in one of those TERK antennas? I have one of the smaller of the two sizes they came in, with 2 inputs and two outputs. Got it for free a long time ago. Used it with DirecTV for several years, and for more years after I sent the box back after they raised the price more. Been up there so long the sun exposure broke its mounting brackets.
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post #20 of 34 Old 02-01-2017, 11:16 AM
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What are the callsigns, networks, and real channel numbers for 22 and 35? We can't tell from your report.
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post #21 of 34 Old 02-01-2017, 11:32 AM
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My GUESS is that you are using virtual channel numbers that look like real channel numbers because you haven't added the decimal point, and mean KRID and KYUU.
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post #22 of 34 Old 02-01-2017, 01:01 PM
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I presume you mean the fol. Terk TV44 Outdoor Loop Antenna that Clips onto the rim of a D* Dish.....clearly NOT intended for UHF and Hi-VHF performance is severely limited by being clipped onto the Metal Dish. Maybe ok for SOME locations that have VERY Strong Hi-VHF (and even UHF) signals, certainly NOT suitable for your location [or most ANYONE else's]....BLEEETTTCCHHHHH:
https://images-na.ssl-images-amazon....15GBAJXQDL.jpg
http://www.terk.com/outdoor-antennas/?sku=TV44

Or maybe you mean the fol. Terk HDTVo Outdoor Antenna, which looks like a Terk HDTV UHF LPDA plus a Hi-VHF Dipole that has been swept forward:
http://www.parts-express.com/Data/Default/Images/Catalog/Original/210-238_HR_0.jpg
UHF Gain of HDTVi/a is about 7 dBi, but Hi-VHF Gain would be only a few tenths of a dB more than an unbent Dipole, about 2.2+ dBi. You need a MUCH Higher Gain Hi-VHF Antenna....and there are better Outdoor UHF Antenna alternatives.

Although larger than Indoor Mohu Leaf models, the Outdoor Mohu 60 is still a LOW-GAIN, 1-Bay Bowtie UHF Antenna with NO Reflector and minimal Gain in Hi-VHF Band (for Ch7, 9, 10 and 13)...and of course Mohu refuses to publish Gain Specifications, so based on 4nec2 Models for "similar" 1-Bay Antennas, I'm guessing UHF Gain is about 3-5 dBi [more on higher Channels] and Hi-VHF Gain is somewhere between 2-3 dBi....both Bi-Directional with NO Multipath Suppression from the REAR.

================================================== ========
To suppress Multipath from the REAR and SIDES, as wall as to POWER THRU those Semi-Truck Reflections, you need a Medium Gain COMBO Hi-VHF/UHF Antenna, such as W-G HD7694P:
http://www.winegard.com/kbase/uploads/HD7694P.pdf [Add 2.2 dB to Spec Gains, which are in dBd vice usual dBi.]
https://www.amazon.com/Winegard-HD76.../dp/B001DFTGR4 [Be sure to click on "Other Sellers".]

Or [since I believe that a 4-Bay Bowtie Antenna has significantly BETTER Suppression of certain Multipath conditions] a Medium Gain UHF (ONLY) 4-Bay Bowtie with Reflector, for example MUCH less expensive Solid Signal HDB-4X, or CM4221HD (ULTRAtenna 60), or A-D DB-4e, etc:
http://photos.imageevent.com/holl_an...2%20-%20RG.jpg [Comparison: HDB-4X curve probably close to CM4221HD.]
PLUS a Medium Gain Hi-VHF Antenna, such as inexpensive Stellar Labs 9-El Hi-VHF FD-Yagi:
http://imageevent.com/holl_ands/yagi...agistellarlabs [4nec2 Model Gain Calculation Results]
https://www.amazon.com/Deep-Fringe-D...r+labs+30-2475
And a VHF/UHF Combiner (aka UVSJ) from either A-D, Hollands (out of stock?), Pico-Macom, Stellar Labs, R-S or Blonder-Tongue:
https://www.amazon.com/Blonder-Tongu...C3C9FKXV22GGMP
If you decide to use inexpensive RCA Preamp, it has SEPARATE VHF and UHF Inputs, so UVSJ not needed.

Aim not quite half-way between 165-deg (re True North) and 128-deg, tweaked more toward the weaker Stations...say about 135-deg.

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post #23 of 34 Old 02-01-2017, 01:25 PM
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Looks like Weiser, ID

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rabbit73: Since you determined his Lat/Long, are there any concerns in his FMFool Report???
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post #25 of 34 Old 02-01-2017, 02:25 PM
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Looks like Weiser, ID
Wellll.. I cheated and hovered over a map until the lat and long looked close, picked the bigger town, then went and got a beer. Thanks Fixed it.

Walking the fine line between jaw-dropping and a plain ol' yawn.

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post #26 of 34 Old 02-01-2017, 02:55 PM
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I cheated even more to refine his coordinates beyond two decimal places, assuming he was not going to tell me....

Maybe he will confirm that it is Weiser, since it is a requirement of the sticky.
https://www.avsforum.com/forum/25-hdt...-1st-post.html

estimated FM signals:

http://www.fmfool.com/modeling/tmp/a...b/Radar-FM.png
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post #27 of 34 Old 02-01-2017, 11:22 PM
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There is only ONE Strong FM signal....on 99.5 MHz, which COULD cause second Harmonic Interference to KBOI (Ch9), which presumably carries CBS, The CW+ and GRIT:
https://en.wikipedia.org/wiki/KBOI-TV
If there are any problems receiving Ch9, an FM Filter should be used on Preamp Input [or if NO Preamp, anywhere between Antenna and Tuner] to suppress the FM Band signals.

Note that Network assignments in TVFool Report are out of date.
Fol. rabbitears report for Boise, ID [Market #117) should be better:
http://www.rabbitears.info/market.php

Note that KNIN (Ch10) is now broadcasting FOX:
https://en.wikipedia.org/wiki/KNIN-TV
And fol. Wiki article says that KTRV (Ch13) carries ION and MeTV, and just dropped MyN....last not yet shown in rabbitears:
https://en.wikipedia.org/wiki/KTRV-TV

You should check you local OTA [NOT Cable] TV Listings to verify where they reshuffled all of the Network Assignments....and more changes are possible in the future years as they shut down Ch38-52 and reshuffle the Deck....again....

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post #28 of 34 Old 02-01-2017, 11:31 PM - Thread Starter
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Yes, Weiser, Idaho. KRID and KYUU. The Mohu Sky 60 isn't picking them up but it does get 32 other sub channels.

The TERK TV44 got what the Mohu does, plus KRID and KYUU but often had problems getting KBOI virtual channel 2, real channel 9 and OPB virtual channel 13, don't know its call letters or real channel, in Payette, ID.

So tomorrow I shall experiment! Instead of spending money!

I picked up a diplexer for $0 and will try using its DC blocking side to feed the Mohu into input one of the TV44 and will replace the Mohu's amplifier with the power injector I had been using to power the TV44. I've straightened out the curve in the TV44 (on the advice of the retired US Navy radioman and all around electronics/radio wizard I know) and will design and 3D print a mount to clamp around the rod where it enters the amplifier housing, and around the Mohu's mounting pipe. Retired radioman's TV antenna setup combines three separate units, one for high VHF and two for UHF, which are aimed in different directions. VHF and one UHF towards Boise, one UHF towards Payette (Clay Peak) to pick up the OPB repeater.

If it doesn't work that way then I'll put the diplexer in between the cable from the house and both antennas.

The goal is to get more channels, reliably, while spending hardly any money other than a few cents worth of 3D printer filament. I don't need to get all the little low power stations in the Boise area, their signals can't make it over to here anyway due to terrain etc.

What about the printer cost? It's one of those Monoprice Select Mini ones. Got it on JET for under $170 and it's already paid for itself by printing some items I sold*.

*A commonly broken plastic piece for a motorized carriage on a Brother knitting machine. Replacements not available, until I measured, modeled in 3D and printed some.
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post #29 of 34 Old 02-02-2017, 07:29 AM
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Yes, Weiser, Idaho. KRID and KYUU. The Mohu Sky 60 isn't picking them up but it does get 32 other sub channels.[
They are your two weakest channels. You need a better antenna and a better preamp for them.
Quote:
but often had problems getting KBOI virtual channel 2, real channel 9
Neither antenna has much gain for real channel 9.
Quote:
OPB virtual channel 13, don't know its call letters or real channel
OPB is K15DY, real channel 15, at 165 degrees.
http://www.rabbitears.info/market.ph...callsign=K15DY
Quote:
I picked up a diplexer for $0 and will try using its DC blocking side to feed the Mohu into input one of the TV44
If you don't have Dish now, why are you messing with satellite diplexers and feeding one antenna into another?
Quote:
and will replace the Mohu's amplifier with the power injector I had been using to power the TV44
Bad idea. A power injector is not the same as an amplifier. You shouldn't be using ANY of the satellite equipment, except maybe the coax if it is in good condition. The TV44 doesn't use power; the LNB does.
Quote:
If it doesn't work that way then I'll put the diplexer in between the cable from the house and both antennas.
Are you trying to combine both antennas? Another bad idea.

What are you using for reception, a TV or a satellite receiver?

Try to keep your system simple to avoid creating problems you can't fix.
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post #30 of 34 Old 02-02-2017, 12:30 PM
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Since you don't want to spend very much $$$, let me throw out a few Quick & Dirty DIY Hi-VHF Antennas for your consideration...which would require a VHF/UHF Combiner (aka UVSJ) from either A-D, R-S 1502586, Pico-Macom, Holland (Out-Of-Stock???) or Blonder-Tongue:
https://www.amazon.com/Blonder-Tongu.../dp/B004BTY700 [It's a DIPLEXER, NOT the usual RF Combiner.]

a) Hi-VHF QICT Loop (note Diameter depends on Element Thickness)...about 1.4 to 2.2 dB higher Gain than RabbitEar Dipole....much better than what you have, but PROBABLY not enough Gain increase.....
QICT (Quarter Inch Copper Tubing), typically used for piping water to Ice Maker is BEST, although you CAN use smaller wire sizes, with some degradation to SWR. Can mount on a simple Wood 2x4 Upright (even better if non-conductive Vinyl]:
http://imageevent.com/holl_ands/loops/vhfloop

b) Hi-VHF QICT Twin-Loop [Figure-8, two Interconnected Circular Loops]....about 4.4 to 5.2 dB higher Gain than RabbitEar Dipole.....Results In Process....will Upload "soonish". Performance similar to fol. UHF Twin-Loop Version, except 3X Larger. Can mount on a simple Wood 2x4 Upright (even better if non-conductive Vinyl]:
http://imageevent.com/holl_ands/loops/hivhftwinloops

c) Hi-VHF Hourglass-Loop (AWG10/12 House Electrical Wire or thicker...NO need to Strip Insulation)..about 3.1 to 3.9 dB higher Gain than RabbitEar Dipole if NO Reflector Rods:
http://imageevent.com/holl_ands/loop...fhourglassloop
Can mount to 3/4-in PVC Rectangular Frame (with additional Horizontal Cross-member in Middle for mounting Central Feedpoint (where Balun Connects).....and rigidity.

d) And my Optimized DIY FF4 4-Bay Hi-VHF/UHF COMBO Antenna provides High Gain in BOTH Bands, although Hi-VHF SWR is a bit higher than desired:
http://imageevent.com/holl_ands/mult...aybowtienorefl [NO Reflector Version]
http://imageevent.com/holl_ands/mult...dblanglreflopt [With Double Angle Screen Grid Reflector]
https://www.avsforum.com/forum/25-hdt...l#post44801233 [User Photos]
https://www.avsforum.com/forum/25-hdt...l#post38699833 [DIY 4-Bay Construction Examples]

Last edited by holl_ands; 02-02-2017 at 12:52 PM.
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