Tech / Special Interest → Electronics > Using cable TV drop amplifier for HD radio

Using cable TV drop amplifier for HD radio

Has anyone had luck using a drop amplifier (around 15 dB gain) to amplify the signal from a passive indoor FM radio antenna? By itself, the antenna does a decent job on FM, but the signal isn't good enough for reliable HD Radio reception. The fact that my house has hills on all 4 sides makes reception difficult.

These amplifiers (especially older ones that do not have a reverse path) are available dirt-cheap used. For the intended use, a one-way amp is perfectly fine.

Obviously, there is stuff (from companies such as Magnum Dynalab) that is specifically designed for my purpose, but nothing used is presently available and recent car repair costs make buying new impractical right now.

I could be wrong, but I suspect that the circuitry inside these CATV amps is vastly superior to what is inside of a cheap indoor amplified antenna.

IIRC there is one guy on AVS who did exactly this and seemed to work out fine. It's been ages. Let me see if I can find it...

Here we go: »www.avsforum.com/t/1228917/passi···insignia

If you watch the video in post #4 you'll see he's using a standard distribution amp. I imagine a drop amp should not be any different as long as the FM frequencies are covered.
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I swear, some people should have pace-makers installed to free up the resources. Breathing and heart beat taxes their whole system, all of their brain cells wasted on life support.-two bit brains, and the second bit is wasted on parity! ~head_spaz

Thanks for that info. I see that the 2 drop amplifiers I picked up this morning to experiment with cover 51 - 1000 MHz, so 88 - 108 is well within the passband. So far as I know, neither amplifier incorporates an FM trap.

I will have to watch the video tomorrow, since I just finished repairing the power supply on a Dell PowerConnect 2716 Gigabit switch that I bought for $1. No more energy today.

OK, I had a chance to watch the video- quite interesting, but the directional coupler would not be needed for a "normal" radio which has separate antenna inputs and audio outputs.

I suspect that the CATV drop amplifier has superior circuitry to the amplifier he used, but I cannot say for sure, since I don't know the model number of his amplifier and I don't have the specialized RF testing equipment needed to compare the amplifiers. His amp looks similar to what Radio Shack sells, but theirs is chrome finish and his is black; the internal circuitry may or may not be the same for the chrome and black models.

Too bad that he did not show a picture of his antenna setup; to the best of my recollection, he did not even say if it is indoor or outdoor.

The thing you have to remember about amplifiers is that if the signal being amplified already has a low S/N ratio, it won't be any better coming out of the amplifier, as it will also amplify the noise, as well as introduce a little bit of additional noise itself.

Sometimes it can help though it the receiver's front-end RF amplifier is very noisy at high gains and the external amplifier has a lower noise figure.

Where such amplifiers come in handy is to compensate for transmission line (coax) losses, or, in the case of the guy on AVS, to compensate for insertion loss of his directional coupler.

In a CATV installation, drop amplifiers and distribution amplifiers are typically used to compensate for losses that occur over the coax drop or the distribution system (splitters and coax) inside a building. Note that the amplifier is inserted AHEAD of the drop.

I've tested a few of those cheap "active" FM indoor antennas. Crap. They often perform more poorly than a proper FM dipole. Again, if the signal being received by the antenna is already poor S/N, amplifying it won't help the situation.

My recommendation: install an outdoor directional antenna. Signal from outdoors at roof height will already be a significant improvement from any indoor antenna. The directionality will also provide a stronger signal with reduced noise when aimed toward the broadcast transmitter.

Old VHF yagi TV antennas are great for this. You can find one for free easily enough.

Thank you for your insight. I am well aware that an amplifier can make the reception worse, instead of better, but it is worth experimenting, especially if the cost is minimal.

In my situation, an indoor dipole doesn't work well at all. An RCA/Audiovox ANT122R passive "rabbit ears" works halfway decent on FM, but the HD light keeps flashing on the radio, meaning that it cannot maintain lock in HD mode. Preliminary results with one of the 2 amplifiers I bought yesterday are encouraging, but I need to do more experimentation.

As it turned out, there was a Magnum Dynalab FM antenna in Craigslist yesterday, but it was located about 300 miles (round-trip) from me- too bad that it wasn't closer. Unfortunately, there usually isn't much interesting stuff in the San Diego Craigslist- the deals tend to be in Los Angeles and Orange County. But, this involves a lot of driving.

I am sure that an outdoor antenna would work better, but climbing on roofs isn't my thing. Plus, there are neighborhood restrictions against outdoor TV antennas. So, this doesn't appear practical for me.

Rather than an outside antenna, you might try placing one in the attic. That is what I used for my FM receiver and it worked well

Of course it will work, but if you live close to any near by FM transmitters you might be doing more harm than help. FM radio stations often times transmit with 100,000 watts of power. If you live close to one of these, this may overwhelm weaker signals throughout the band, even without amplification. Amplification can easily overload the receiver and make it's selectivity even worse.

Yes, that is always a possibility.

As far as the amp goes it should work just fine. The important question is why are you having trouble picking up the HD? While on the surface it looks like you have a weak signal, that may not be the case. The other possibilities are adjacent channel interference and multipath. For a weak signal the amp could help, for the other two, it will likely make the trouble worse.

FM Broadcast HD, which is a digital carrier, is actually transmitted in the first adjacent channel on either side of the analog carrier. With the proliferation of 2nd adjacent translators, there is very little separation between the two, leading to a high probability of cross interference.

Unfortunately, without a spectrum analyzer and other specialized RF testing equipment, it is impossible to say exactly why the HD isn't locking, so all I can do is try different things to see if the situation can be improved.