Originally Posted by summguy
I have a yagi-style UHF antenna (digiwave, one of their longer units) and I added a 5 mm wire mesh to the back reflector to improve forward gain. The antenna is currently pointed 90 degrees away from the local TV tower (RF channel 10). There is no amplifier.
I can receive the following channels on my Samsung LN22A330 22" TV: 10, 14, 18, 20, 29, 69. All of those channels are both real and virtual except for 69 (that's OMNI, and their channels are confusing, but it's either real channel 20 or 40).
Note: If you have a working channel on RF 20, we can safely assume channel 69 is not on RF 20. (You wouldn't be able to receive either one if it were.) Therefore it is likely on RF 40.
So you tell me if a UHF yagi antenna, with no amplifier, pointed 90 degrees away from a local tower 1 mile away broadcasting on VHF channel 10, is going to interfere with the reception of UHF RF channels 18, 29 and 20 (or 40).
In free space, that might be a good argument. But I'm betting your antenna is near the Earth's surface, where there are lots of buildings, trees, etc.
As a result, a few reflections of channel 10 are going to reach your antenna no matter how it's aimed. I wouldn't expect a UHF antenna to have any gain at a VHF frequency, but you are only one mile away!
BTW, I checked your link. Interesting that Mediasonic has moved to yet another hardware version (and that apparently, they've given up trying to number their firmware versions. Given the crazy progression of their firmware revisions (V3-V10-V12-V8-V13-V14-V1, and I probably left out a few), that's probably for the best.
Anyway, in my experience the HW tuners do seem more susceptible to overload than most others. True, I don't have your exact model, but the evidence you've provided nevertheless points to it. If an overloading signal is received, it drives the electronics into non-linear operation that will cause both harmonic and IM distortion on all
channels - not just those near the frequency (or a harmonic) of the strong signal. All that distortion looks just like noise to an ATSC demodulator, reducing your S/N ratio.
Note that RF 18, 29, and 40 are all 11 channels (66 MHz) apart. IM distortion from the first two could easily wipe out reception of the third; likewise, IM distortion from the last two could wipe out reception of the first.
Now, what to do about it? The way I see it, you have three choices:
- conclude the HW tuner is junk, send it back, and opt for a different tuner that won't overload so easily;
- since splitting/weakening the signal helps, split/weaken it more, e.g., with a 4- or 8-way splitter; or
- just attenuate RF 10. Since all your other channels are UHF, that should be easy. I'd probably put in a $4 UVSJ, connect the UHF antenna to the UHF input, and connect the UHF/VHF output to your splitter. At this point channel 10 should be all but gone, but if I'm right all the UHF channels will work.
To restore RF 10, you can connect a small indoor antenna to the UVSJ's VHF input. As I said in a previous post, even an unrolled paper clip would likely be enough.