Reception Troubleshooting in Dayton, OH

Longtime lurker, first time poster! This community has already provided an incredible amount of valuable advice over the past few years, but now I need advice for my specific situation. First, my TV Fool report:

I am under 5 miles from my local transmitter farm, and 10 stations transmit from that general area. I chose the unidirectional UHF Channel Master CM-4220HD in an attic installation 20-25 feet above ground level. I have tried azimuths of 270 and approximately 315 degrees. The signal travels though 50 feet of new RG-6 coax from Monoprice directly to a Samsung UN60H7150A TV in my basement.

My problem is that TV's autoscan is not picking up all of the local stations. At an azimuth of approximately 315 degrees, channel 16 was the most consistently good, while 41 and 26 were the worst or not picked up at all. When I pointed the antenna more directly at an azimuth of 270 degrees, channel 16 disappeared, but all other "green" stations are clear. There are also several FM stations in the local area that I believe transmit from the same location. My TV doesn't display very helpful signal diagnosis information, but the clear channels show SNRs of 20-34 dB.

My current hypothesis is that my tuner is suffering from multipath, FM interference, very high signal strengths, or a combination of all three. I plan to buy the $4 FM trap and $13 variable attenuator from Antennas Direct. Do you think I'm heading in the right direction?

Thanks in advance for any help!
I don't understand why you're pointing the antenna at 315 degrees. Your TV Fool report indicates that nearly every station in your area is between 270 and 250 degrees.

As for channel 41, you appear to have a number of adjacent channels, but that doesn't explain the issues on 26 and 16. That indicates that multipath might be an issue. So I'm curious how your house is set up for HVAC: Do you have metal duct work in your attic? Is your HVAC unit located in your attic? What about can lights or electrical wiring? Skylights? Are there any other sources of potential multipath interference inside the attic or upper floors?

Also, have you adjusted the position of the antenna within the attic itself? Surely you can move it around up there to see if reception is better in another location? Sometimes moving an antenna 2-3 feet horizontally or vertically is all that's necessary to get good signal.

Fringe Reception

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:welcome: AeroScott,

ATL is spot-on about metallic items potentially being unpredictable signal reflectors that can confuse your TV signals. However, since you are having problems with so many channels, I think there is more to consider. Does your attic have foil-backed insulation in the floor or on the walls? Do you have a metal roof or metal siding?

Personally, I have not had any issues with adjacent channel interference nor signal strength overload in spite of living within a mile of several high-power transmitters using high-gain directional antennas (see my photo albums here). Also, I tested a cheap $49 battery powered portable TV set within one block and again at seven blocks distance from the above mentioned transmitters and had perfect reception: three of four of them have close to 1 million watts ERP.

No more than one or two of your TV channels are apt be affected by strong FM Radio signals, so I doubt that's your problem and an attenuator might be your solution, but lets try something else, first.

Have you tried a simple set of rabbit ears or even a length of wire inserted into the antenna socket on your TV? That will give you a 'base line' of channels you CAN receive. Next, is to be able to collect them on your CM-4220HD which is not unidirectional, but can receive stations across (roughly) 180 degrees.

Aside from foil insulation / metal siding etc (above) I suspect the antennas' built-in balun is faulty and is not passing signals properly. I have a copy of that antenna and the balun is a bit flimsy.