Another Which Amplifier Question.

[BobHelms]

Hello,
I using 2 Channel 7-69 yagi antennas. I do not want to use a rotor. One is pointing 126*, the other 296*. The masts are 20' apart at the same elevation. I coupled them with a CC-7870 to 1 HDTV. I could then receive most of my target OTA transmitters. They are 4.1, 5.1, 11.1, 17.1, 20.1, 22.1, 28.1, 30.1, 47.1, & 50.1. But some days the signal levels would go up and down on stations (4.1 & 30.1) that normally average 5 out of 10 bars on my (built in) TV signal strength meter and sometimes 30.1 goes away completely. After understanding the facts about the losses associated with the CC-7870 I surmised (SWAG) that my signal fluctuations were due to the coupler loss. In an attempt to make up for the CC-7870 loss I installed a AP-8700. Bad idea. Now I can't lock onto any signals, constant breakup. So now I'm thinking that maybe the signal is too strong. Then I thought that it might be a good idea to ask someone who knows more about this that I do. So I've attached a TVFOOL report. I'm hoping that maybe a HDP-269 will solve my problems. I don't understand why a solid 8 out of 10 signal will at times yo-yo up and down during a bright sunny day and at night not budge from the 8 mark. So TIA for any advice / suggestions.
Bob Helms

[winegard]

Good morning Bob -

Here is the response from technical services.

There could be a couple of issues with your antenna system. One being multipathing between the antenna when they are coupled together and overload from the preamplifier.

The first thing we need to check is how each antenna receives signal independently. To do this connect only one antenna to the CC-7870 without a preamplifier and check the channels received by this antenna. Set the HDTV set or set top decoder box to “auto-scan” and note all the channels received. Then do the same for the second antenna. With all of the channels noted from each separate antenna now combine the two antennas without the use of a preamplifier, and note which DTV channels were lost or became marginal. You might also check each antenna independently without the CC-7870 to see what affect the 3.5dB (30%) signal loss has on the reception of each antenna’s DTV channels.

The marginal reception may be solved by tuning (adjusting) either antenna slightly for optimum reception of those channels.. In some cases both antennas may need a small adjustment. I would only use a preamplifier if the use of it provides more DTV channels or stabilizes marginal channels.

Test the preamplifier with each antenna using the test process described above for each antenna. The preamplifier suggestion would be the HDP-269 if one is needed. If the preamplifier helps each antenna without the CC-7870 in the line it is possible that a HDP-269 preamplifier may be needed on each antenna to overcome the CC-7870 insertion loss and you would install the CC-7870 after the power supply of each HDP-269.

You may need to use an infrared A/B to combine your two antennas and switch between them if you can not combine the two separate antennas. This will prevent them from causing the multipath problem.