antenna upgrade

[ta240]

my report is at:
http://www.tvfool.com/?option=com_wr...e2cb0f4d26ec9f

The only channels I'm really interested in getting are: 9, 10, 48, 35, 20, 43 which are all at 159 degrees.

Currently I have an antenna at about 20 feet up. It is one with 4 bow-ties on two panels, Antenna's direct DB4e . I have a small yagi antenna mounted above that to get channels 9 and 10. They go into a signal combiner and then into a pre-amp (originally a CM 7777 but now a Wineguard boost xt-20) then 60 feet of RG-6 into a splitter that goes to the TV and to a HD Homerun tuner.

It worked quite well for 6 years. Occasionally channel 9 would drop out but mostly they all came in decently. But just the other evening I lost all channels. When I checked the HD Homerun signal strength it showed 100% on signal strength but around 55 on quality. Then it would drop to 30 on quality and then lose all signal. Then it would repeat. I thought maybe the signal was over-amped with the CM 7777 so I swapped in the boost-xt (out on the ladder at 10 PM in the dark) and all the channels came back.

I thought everything was great until the next evening around 7 when channels 9 and 35 would drop out and then come back after awhile over and over again. I'm not sure if the signal with the lower amp just isn't enough for those two now. I don't have any tall trees closer than a half mile away and even then there aren't many but I was wondering about trying to raise the antennas a foot or two. Or if it would be better, since all the channels I want are in the same direction, to switch to an antenna like a CM-2018.

It looks like channel 9 may always have issues with being a slightly weaker signal and having another channel 9 coming from the other direction but 35 looks like it should be decently strong.

Suggestions are greatly appreciated.

[ta240]

After more reading I'm actually wondering if I'm going the wrong way with trying for a stronger signal. Maybe I'm still getting too much even with the lower power pre-amp.

Since the channels that have problems always have them after dark when the signals should be stronger with less noise are they just crossing the limit of being too strong at that point?

I may not be able to do anything about channel 9 since the other channel 9 would get stronger after dark too and that is already a directional antenna.

Should I try adding an adjustable attenuator? and back the signal off a bit

[Tower Guy]

Your signals look strong enough to feed your TV and HD Homerun without a preamp. However, the strength of the TV signals should pose no problems to the new preamp. It is possible that strong local FM signals are causing preamp overload. Try your antennas with just a UVSJ combiner (don't use a backwards splitter) to see if reception of channel 35 improves. If you find that you need a preamp, try the inexpensive RCA PRAMP-1R, it has seperate inputs for VHF and UHF. Internal to that preamp are two independent amplifiers which help reduce overload.

In order to receive channel 9 from Sacramento you will need to reduce the strength of the northern channel 9 more than the front to back ratio of your existing VHF Yagi. The cheap approach is to mount the antenna lower on the south side of your house to attempt to use the house as a barrier to the northern signal. The more sure fire solution is to mount a pair of identical VHF yagis 7' apart and carefully aimed to minimize the signal from the northern channel 9. To learn about stacking antennas to reduce interference, read the ganging section of the HDTVprimer.

[rabbit73]

The FM signals don't look like a serious problem based on my estimate of your location:
http://www.fmfool.com/modeling/tmp/9...b/Radar-FM.png

I don't understand how the two-antenna trick can null KIXE co-channel interference because it is in the opposite direction.
http://www.hdtvprimer.com/antennas/ganging.html

I think it would take stagger stacking to improve the F/B ratio.

The only channels I'm really interested in getting are: 9, 10, 48, 35, 20, 43 which are all at 159 degrees.

They are not all in the same direction, 43 and 20 are at 342.

I have a small yagi antenna

Which yagi?

They go into a signal combiner

What combiner?

It worked quite well for 6 years. Occasionally channel 9 would drop out but mostly they all came in decently. But just the other evening I lost all channels.

A sudden change like that indicates a defect in the antenna system like a bad connection or component.

I would have thought trees growing, but you said they were not in the signal path.

[Tower Guy]

I suggested horizontal stacking because KIXE is 21 degrees off the back of the antenna. When set at 7' spacing the first null occurs 21 degrees off the front of the antenna plus 21 degrees off the back of the antenna. Stagger stacking would work, but it's a bit more complicated than horizontal stacking.

[rabbit73]

Ah, so; a null is also created at the back.

Thank you.

[Tower Guy]

I suspect that the sudden problem was due to tropospheric ducting on Wednesday. I checked the Hepburn maps to see that ocean tropo snuck inland.

[Tower Guy]

Originally Posted by rabbit73

Ah, so; a null is also created at the back.

Thank you.

Yes. So here's a true story. In the late 70's I installed a translator in Utica, NY. It retransmitted WNYT on channel 13 from Albany. There was also a channel 13 in Rochester, NY that was 14 degrees off the back of the antenna. The terrain toward Richester was more favorable than the terrain toward Albany. When testing reception with a 10 element yagi Albany was noisy and showed cochannel interference. When aimed at Rochester the audio was fine but the picture was not there. By ganging 4 yagis; two with horizontal stacking and two offset using stagger stacking, the picture from Albany was perfect.

[rabbit73]

Interesting story. Sometimes extreme measures are required to make it work.

How was the quad arranged and combined, the staggered pair in the center and the horizontal pair one each side like this +?

All-coax stacking harness or an air dielectric power divider?

[Tower Guy]

It was a box of four yagis. The top two were mounted forward by a quarter wave. The bottom two were centered. Both pairs were stacked horizontally by the critical distance for a 14 degree null. To aim them I looked at the lower pair on a TV set and nulled the interference. Next I connected the top pair using a extra quarter wavelength of RG-11 coax prior to the tee connector. The antennas were 10 element yagis made by Taco, which are still available from Wade in Canada.

[rabbit73]

Excellent!

Thank you.