Any issue adding a distribution amp? Will it kill HD radio signal? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 5 Old 05-06-2019, 08:34 PM - Thread Starter
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Any issue adding a distribution amp? Will it kill HD radio signal?

Hello, all. I'm looking at splitting one or two of the TV leads in my house so that I will have an outdoor FM antenna. Generally-speaking, I don't need that here, but there are a couple HD signals that aren't totally reliable. Also, the TV antenna I have outside works very well, but there are a couple of low-power local TV stations that aren't completely reliable. So, I was thinking I'd put in a distribution amp (one on which I can shut off the FM trap). A Winegard HDA-200 is what I'm looking at.



HOWEVER, I was reading here this evening, and came across a thread in which a member said they'd experienced elimination of HD radio signals when adding an amplifier to an FM antenna. Is this a generally-known issue? Has anyone else experienced this?
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post #2 of 5 Old 05-08-2019, 01:16 PM
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It would help if you could submit your www.tvfool.com and www.fmfool.com RESULTS so we can assess your OVERLOAD situation....and I could make some predictions for which FM and TV Stations would be affected the most. Since a typical RG-6 Coax has a "typical" Loss of about 2 dB/100-ft in FM Band, the RF Splitter Loss would presumably be the primary reason to justify passing FM Signals thru a Preamp/DistroAmp. However, note that using a Preamp/DistroAmp to provide an extremely Low Noise Figure isn't all that important in Lo-VHF/FM Band since Man-Made Noise is typically many dB Stronger than Thermal Noise, so you may or may NOT see any improvement in FM Reception....and will LIKELY see Degradation to Next Adjacent Channel Rejection (etc) due to the Intermod Products generated throughout the FM Band, which a "naked" FM Tuner would have minimal if any problems meeting "specs":
https://photos.imageevent.com/holl_a...%20Nov1992.jpg [Man-Made Noise in Excess of Thermal Noise]

Winegard LNA-200 has a spec Gain of 18 dB, but Calaveras measured 14 dB Gain in VHF Band (presumably also FM), but Overload Resistance isn't as high as it COULD be. I have NOT seen any LNA200 measurements for Gain in FM Band, which in many Preamps can be MUCH MORE than mfr "spec" number....or ATTENUATED, like in RCA TVPRAMP....perhaps others have more specific info??? We need to see your TVFOOL and FMFool Results to make sure, but I suspect that 18 dB LNA-100 MAY have TOO MUCH Gain, making it more susceptible to Overload Desensitization [or FM Band Attenuation???]....you would be better served by using 15 dB Gain CM3410 [may be used outdoors], with significantly higher Overload Resistance.
https://imageevent.com/holl_ands/fil...=0&w=1&s=0&z=4

Although some FM Stations are co-located with TV Stations....in the many FMFool Results that I've looked at, MANY/MOST are peppered across the landscape, resulting in Strong Stations frequently being much closer than TV Stations...and they end up with signals of all different strengths coming from MANY Different Directions. Which means 2nd Harmonic of strong FM Stations can interfere with reception of TV Stations in Hi-VHF Band (Ch7-13)....and in some unusual situations can also affect some UHF Band Stations.

I recommend AGAINST using a Combo VHF/UHF Antenna to ALSO feed your FM Radios: 1) As I said, you likely have FM Stations in MANY different Directions, which would require rotating that Combo very frequently, usually in a DIFFERENT direction than needed to ALSO receive desired TV Station, 2) Strong FM Signals can result in 2nd Harmonics preventing reception of weak Hi-VHF Band TV Stations, 3) If you pass MULTIPLE Strong FM Signals thru a Preamp/DistroAmp then the Intermodulation Products among those signals can prevent reception of some Weak FM Stations, 4) GOOD, Low-Loss Band Splitters that separate JUST the FM Band (88-108 MHz) from IN-BETWEEN the Lo-VHF (54-88 MHz) and Hi-VHF+UHF Bands (174-698 MHz) are rare...and fairly expensive....fortunately if you aren't feeding both TV and FM in the SAME Room, you wouldn't need one in that location, and 5) In order to separate out the FM Band, the Tin-Lee S7-TF can't help but attenuate portions of the adjacent Ch6 TV Signal (82-88 MHz), as well as 1.4 dB attenuation on Bottom part of FM Band (88 MHz) and 2.5 dB attenuation on Top part of FM Band (108 MHz):
http://www.tinlee.com/PDF/S7-TF.pdf

I ALSO recommend AGAINST combining an FM Antenna with whatever you use for TV Reception, even if combined on the OUTPUT of the TV Preamp to reduce 2nd Harmonic and FM Intermod Distortion....for same reasons as above....PLUS you are going to need one more of those expensive Tin-Lee S7-TF TV/FM Band Splitters to combine the FM Antenna with your TV Antenna(s).

What I DO recommend is to use a separate Coax Downlead and Distribution System for a PAIR of FM Antennas....the first being a Low-Gain TRUE-OMNI (i.e. Double-Hoop type) which would be the Primary Antenna signal. And if you want to listen to even weaker FM Stations, a dedicated medium to high Gain FM-Band Antenna (on a Rotator) that goes thru an A/B FM Switch to feed either just one "favored" FM Radio or perhaps the entire FM [or TV?] Distribution Network....or a THIRD FM Distribution Network to each room. FYI: Radio Shack made an A/B RF Switch with IR R/C...which could be part of a whole home IR Distribution Network.
https://www.amazon.com/Stellar-Labs-.../dp/B00DHHOZBI
https://imageevent.com/holl_ands/omni [Double-Hoop (c) is TRUE-OMNI....most others, incl. Turnstiles, are Bi-Directional with NULLS]
https://www.radioshack.com/products/...ion-a-b-switch [R-S may not exist anymore]
https://www.amazon.com/Radio-Shack-R.../dp/B000H50L9S [Pricey used units.....]


Feel free to do whatever is easiest for you....just be aware that more $$$'s can yield more benefits....if you even care....
As a bare minimum, you might want to Combine the Stellar Labs Double-Hoop FM Antenna with your existing TV Antenna using a Tin-Lee S7-TF....plus at least one more for your Primary TV+FM listening room. This would supplant the Directional FM Gain [IF ANY] of your existing TV Antenna(s), with the Double-Hoop's TRUE-OMNI Gain in ALL Directions, so it wouldn't MATTER which way the TV Antenna is pointed.

Last edited by holl_ands; 05-08-2019 at 02:32 PM.
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post #3 of 5 Old 05-08-2019, 08:21 PM - Thread Starter
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Wow! That's an excellent answer! Thank you! I hadn't even considered overload, but it's clear that may be a problem for me. I'm having trouble with the URL from tvfool for some reason (almost certainly me), and fmfool doesn't have that, so I'm trying to insert images of those pages here:

I suppose I'm somewhat lucky here insofar as ALL television signals receivable by me come from the same direction, with only a few degrees difference in bearing, and _most_ of the FM radio signals I'm concerned with (digital signals) are on top of the exact same ridge. I'm also a ways uphill from the rest of the metro area. There are a couple that bear a bit 'left' of those, and that's what I'm trying to pull in on the FM HD side. Still, there are some other FM stations that are pretty strong from other directions, and I hadn't really considered their potential impact here.


I'd say my biggest issue is the constraints of my house. I can't put any sort of antenna outside other than the small directional I have there now. My roof is concrete tile, which is covered essentially entirely with a solar array, and it has a metal radiant barrier on the underside. The A/C indoor unit fills all the space in the attic that is simultaneously available and accessible.


From what you're telling me, perhaps I'll re-think the notion of trying to pull the couple of distant or low-powered HD Radio signals.
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post #4 of 5 Old 05-09-2019, 11:23 PM
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FM Tuners typically use MULTIPLE RF Stages prior to the Mixer that downconverts the Tuned Channel to 10.7 MHz IF Freq. The 10.7 MHz IF Strip provides lots of suppression of Next Adjacent Interference (and in some Tuners also from Adjacent Channel). Each of the RF Gain Stages follows a Tuneable Filter that TRIES to suppress Channels other than those near the Channel of Interest. Hench each Stage reduces the RF Bandwidth, eventually suppressing all RF signals except for within a few MHz of the Tuned Freq. So a "naked" FM Tuner has been intentionally designed to be more or less immune to Interference from other FM Band Signals....even very strong signals.

However, when you pass YOUR very strong FM signals thru a PreAmp/DistroAmp, Intermodulation Products will be generated across nearly ALL FM channels (per my IMD Calculator)....blocking reception of the weaker FM Stations. Unfortunately, I can't predict WHICH weaker stations will be lost, since I don't know the IMD characteristics of individual equipments.

So you should NOT amplify FM Signals....

More info re: FM Tuner Sensitivity etc:
https://www.avsforum.com/forum/154-h...l#post57653694
Note that cited link confirms that FMFool "Red" Zone stations are too weak to receive with 2 dB Gain OMNI Antenna (higher Gain Antenna can help). So, with OMNI Antenna and without PreAmp/DistroAmp, you "should" receive "most" Analog FM stations in "Yellow" Zone and likely ALL in "Green" Zone. [If NOT, be sure to let me know if my calculations aren't in the right ballpark....] BTW: HD-Radio Sensitivity will likely be worse...but I don't have a guesstimate for how much at my fingertips....

FYI: Ledgerboard, Eave and Chimney Mounts are available so you don't have to attach ON roof...and higher is better to avoid signal blockage from house:
https://www.google.com/url?sa=i&rct=...57557620680380
https://www.google.com/imgres?imgurl...act=mrc&uact=8
https://www.google.com/imgres?imgurl...act=mrc&uact=8

Last edited by holl_ands; 05-10-2019 at 12:05 AM.
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post #5 of 5 Old 05-10-2019, 07:37 AM - Thread Starter
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Yes, I receive most of the ‘green zone’ stations’ in that list with just an extendable mast, at least when I’m upstairs. That’s analog only, though. A couple in there I can’t reliably lock the digital/HD transmission, and it’s a digital sub channel here and there that I would like to be able to listen to.

I appreciate the mount bracket links. As far as external antennae (or is it antennas when speaking of inanimate objects?), that’s a rules issue rather than a mounting issue. Too, running antenna leads within the house is a deal-breaker for my wife. :-) Our existing ones were built in when the house was built.

I’ll see what I get without a distribution amp over the summer and go from there.

Thanks again for the thorough answers!
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