In sci.electronics.repair, on Thu, 27 Aug 2015 13:29:15 -0700, Jeff
Liebermann wrote:

On Wed, 26 Aug 2015 02:50:55 -0400, micky
wrote:

To use one splitter as a combiner, for two antennas,
and the other splitter as a splitter, to feed the signal to a DVDR and
to a digital-to-analog set-top box that feeds a VCR.

You have a possible problem. When you take two antennas and combine
them with a splitter/combiner, you run the risk of creating a
situation where the two signals cancel. For example, if you have two
antennas, and both pickup the same station, with roughly the same
signal level, and roughly 180 degrees out of phase, the signals will
cancel in the combiner. Worse, you will probably have different group
delays (phase shifts) between the two antennas at different
frequencies and even on different parts of the 6 MHz wide signal. The
result is a "hole" in the frequency respons (gain) of the combined
antennas. What that looks like on a TV is a tolerably strong signal,
but with a truely rotten picture. With digital TV, it can also be the
equivalent of the old "ghosts" problem, where you have two signals
arriving at different times, resulting in 2 pictures. However, with
digital TV, it just results in a poor quality picture.

Combiner schemes work if:
1. The two antennas can't "see" each other and cover different TV
stations.

That's the way they are now.

They now each cover one tuner (the DVDR or the set-top-box/vcr), which,
via an A-B switch, feed the same set of televisions.

2. The two antennas are for different frequency bands, such as VHF
and UHF. You'll need a diplexer to do that, not a combiner.
https://www.google.com/search?q=vhf+uhf+tv+diplexer&tbm=isch
3. The two antennas are identical and are pointed in the same
direction. That will give you 3dB more gain, but you'll either a

3db is about 2x as strong? Yes, Wikip says power ratio is about 2,
amplitude ratio is about the square root of 2. I asked Solid Signal
if splitting the signal to go to the VCR and DVDR would cut the strength
in half and he said, No, only 3db. Then he wanted to know where I
live so he could give me distance and heading to the stations, and then
recommend a second antenna. He didn't pronounce attenuator right,
either. Oh, well.

phasing harness, or two amplifiers and resistive combiner to make it
work.

I suggest you get rid of the two antenna scheme and combiner for now
and see if one antenna works better. Also, you can make it work with

I have one antenna for each device now.

I see the problem and since I was smart enough to think of the DC
voltage problem, I should have thought of what you just said.

Interestingly, the guy at Solid Signal was one who recommended two
antennas and he didn't say a word about it either. And he certainly
didn't push identical antennas or facing them the same direction.

Thanks for warning me.

an RF switch between antennas, which admitttedly isn't convenient.

I'll address the rest later. Customer bearing checkbook just
arrived...

Yes, more important.