Our current television setup uses a roof mounted antenna similar to this:
This antenna feeds 3 different receivers through 2 RF splitters.
Any antenna that I am able to use for radio transmission is typically low and close to the dwelling. This makes it very easy to overload any cheap over the air television receiver. It seems that most televisions do not implement adequate filtering on their front end.
The solution to this was to install a high pass filter on the first RF splitter input. Since they were of a nice form factor I purchased a filter online instead of building one. I received a "HPF-54" from amazon. It claims to operate with low insertion loss from 54MHz to 1000MHz (OTA TV frequencies) and significantly attenuate signals below this.
 |
| Nice compact filter to go inline with the coax. -AC9LF |
Good results were immediately noticeable on install. This little filter did not appear to attenuate normal TV stations but seemed to completely remove any TV receiver picture or audio breakup when transmitting with my radio at power levels of around 30 watts on 40m, 30m, and 20m (tested so far).
As a quick check I did an impedance scan across the HF band to 30MHz with this filter on the analyzer. The filter was fitted with a 75 ohm terminator. Resistance is zero across most of the HF band with a good amount of reactive component depending on frequency.
 |
| AC9LF impedance scan of HPF-54 |
Measuring the center conductor with a DMM shows that it is DC blocking.
I also did a scan of VHF/UHF with a 50ohm antenna analyzer. The range covered is 137MHz to 1000MHz. There will be some loss in the adapters used as I needed to use a SMA-BNC then BNC-F for this testing. The adapters used don't have very good frequency response themselves. There is also an impedance mismatch as I am testing a 75 ohm system and this analyzer is meant to test 50 ohm systems. However as you can see the VSWR is very low. I would expect 1.5 to be a perfect match in this case due to the impedance mismatch.
 |
| With HPF-54 inline. -AC9LF |
 |
| Without HPF-54 inline. -AC9LF |
Now the TV can be used to receive over the air stations at the same time I am playing with radios. This makes for a more tranquil living area.
Here is a link to the product that I purchased for this post:
Ancable in-Line High Pass Filter Coupler Barrel Adapter 54-1000MHZ 2-Pack by Ancable Direct Learn more: https://www.amazon.com/dp/B074K87HTD/ref=cm_sw_em_r_mt_dp_U_BUCMEb1RY2AY1
If I perform any more significant testing or anything else changes I will report back here.