Problem combining two antennas.

Due to a Tower collapse our local PBS station (kozk) which normally covers this area is not. There is another PBS station (kemv) (southwest) which I'm On The Fringe area of I thought I would try to receive. I Custom-made an antenna for RF Channel 13. this evening I connected the antenna for about 35 ft of coax directly to the TV set. The antenna was resting on a railing on a ground floor deck. The desired station came in without any problem and with a good strong signal. so I climbed up on the roof and mounted it at 3 ft above a VHF UHF antenna that I had pointing towards Springfield Missouri (northwest). The height above ground would be about 30 ft. The two antennas went into antenna combiner. That went into a mast Mount RCA preamplifier. At that point all of the channels came in except the one who should previously been the strongest from Springfield. Things were fine for about an hour and then stations started disappearing. Finally all of the stations were gone. My suspicion was the preamplifier since I had not previously used one. I removed it and just hooked into the antenna combiner directly. At that point all of the Springfield stations returned. I lost the PBS Channel though. And in a weird twist started receiving sporadically a channel from Jonesboro Arkansas (rf8). None of the antennas were pointed in that direction at all. I'm also not receiving the local low power station that comes in with no trouble as I'm only a few miles from the transmitter. Now I'm starting to consider there might be some interference between the two antennas. Are there any rules about spacing? Any other suggestions I might try? Thanks!

Thanks pamajestic and Jim5506. Sorry it's taken so long to get back to this. Tropospheric conditions did have a lot to do with some of the questions I had. But here are further details. I'm combining a home-made 5 element yagi antenna specifically cut for rf 13 with a large radio shack uhf/vhf antenna. The rf 13 yagi is pointed at roughly 200 degrees to try to snag KMEV, Mountain View Arkansas. The uhf/vhf combo is pointed at about 300 degrees aiming for Springfield MO stations at rf 10, 19, 28, and eventually 16. As a further update the RCA antenna preamplifier burned out. It was most likely defective as it was new.

The rf 13 yagi is mounted about 4 feet above the uhf/vhf combo antenna. The coax from each goes into a channelplus 2 input combiner. The common output from that now goes into the house where I've temporarily connected a cheap Wal-Mart ONN preamplifier and injector. I didn't want to get back on the roof until I was sure it was worthwhile. My interest in antennas only slightly overrides my fear of heights. The new results are that I get the intended Springfield stations and the local lptv ch. 36 all of the time. KEMV is fairly reliable, but occasionally I will lose signal for a while. (At most once a day for maybe an hour). I've been getting KTHV (rf12) for a few hours at a time but I'm sure that's due to tropospheric conditions. But it at least proves that the custom yagi is doing its job, I think.

My plans are to make new identical cables for the antenna to combiner connection. I'll be moving the preamplifier and connecting it to the output of the combiner. I'm hoping that lowers the loss for the cable run of approximately 70 feet. If anyone has any other suggestions I would gladly welcome them. I should mention that the TV does not have a signal strength indicator.

harshness said:

Is the use of an antenna switch a possibility?

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Not at present. I don't have a way to run an additional coax inside the house. That may change and I'll have to keep that in mind.

Jim5506 said:

If you can find an old channel 13 Join-tenna by Channel-Master you can insert the channel 13 signal into the cable from the all channel antenna with little signal loss.

Otherwise the signal coming from each antenna will be less than the signal that would be received if there was no combination attempted.

This guy has 4 of them - Channel Master JoinTenna CM 0583, Joiner Combiner, Coupler, Channels 6-13 and 19 | eBay

Oops, ch 13 is sold out.

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The RCA preamplifier had a setting so you could use a separate VHF and UHF antenna. If I dare try another one I may see if the channel 10 signal is strong enough to just use the combo antenna as a uhf antenna and the rf13 yagi as a vhf antenna. I didn't know about Join-tennas. I've have to keep a watch for them.