Interference Sources on OTA, Radio, WiFi Signals

[ota_canuck]

Thanks to the assistance of a IC Spectrum Management Officer, I finally found the culprit of our local broadcast interference. A local taxi group has a radio license for frequency of 165.525 MHz. The base station is about 600ft away on another street in behind my lot, but their cars are always passing right by my house when they come&go on calls. They have 10 vehicles that use that 165.525 MHz frequency.

Any suggestions?

_______________________

He also provided this useful self help link:
http://www.ic.gc.ca/eic/site/smt-gst...h_sf06086.html


Real Video Presentation: Cutting Through... Radio Interference
Play high bandwidth version (450 KB/sec)
http://mmprodnt.ic.gc.ca/mmpub/DGRB//interference.rm

[Jase88]

^^^^^ Notch filter with about 50dB of attenuation.

[roger1818]

ota_canuck, My suggestion is to get a 165.5 MHz notch filter (TinLee should be able to make one for you). It is far enough away from both VHF-HI (174 MHz) and FM (108MHz) that it doesn't need to be a sharp notch. If you ask nicely, the taxi company may even be willing to pay for it. When you get it, you can do some experimenting, but you may need to put it before your pre-amp.

You could also try an HLSJ to see if it will knock it out. If you need VHF-LO, you could join two of them together back to back (LO to LO/HI to HI) and see if that works. It likely won't be as good as a 165.5 MHz notch, but it will be much cheaper.

[Jase88]

I may have mentioned this before, but this page at Industry Canada (see Appendix 4) details how to make a simple quarter-wave or half wave coax "stub" notch filter to attenuate interfering signals.

[balm]

Im testing for poor TV signals in a location which is lower than immediate surrounding lots and houses, and also no AM channels come in

Most TV channels come in around 20% at 20 ft high, even the strong local ones

Reception in surrounding area is otherwise very good


All house wiring appears properly installed.


What can be affecting the AM sand Tv signals so much ?

[Chasseur]

Suppose that I care only about channel 10 and that I want to reduce interference:

Does using a VHF-Hi only antenna can help reducing interference on channel 10, instead of using a VHF+UHF antenna like a 4228? Or maybe a single channel antenna?

[JamesK]

^^^^
165 MHz is a bit below Ch 7, so a VHF high antenna won't do much to help you. A dedicated Ch 10 antenna might. However, that link to solutions provides a possible fix. You need a "T" connector and a short piece of coax & F connector. You start with the cable a bit longer than necessary and start trimming until it works. If you trim too much, then just start with a new piece of cable, cut to where you had best results. A quarter wavelength open line will appear to be a short at the target frequency.

[roger1818]

While Yagis have a sharp drop off above the desired channel, they degrade gradually below so a channel 10 antenna won't help that much. If you only care about channel 10, another option is to get a CM-0580 Channel 10 Join-Tenna (discontinued but still available from the Channel Master store) and use it as a band pass filter on a VHF-HI antenna.

[Chasseur]

I not sure to understand how channel filtering can help reduce interference. I mean, once the interference signal hits the antenna, isn't it too late to filter?

[hoopitup2000]

No, as long as the filtering is done prior to the input of the mast mounted pre-amp..

[roger1818]

^^^ Unless, of course, it is co-channel/multipath interference, in which case the only hope is a more directional antenna that will increase the strength of the desired signal (on axis) and decrease the strength of the undesired signal (off axis). Interference at other frequencies/channels can be filtered out.

[JamesK]

I not sure to understand how channel filtering can help reduce interference.

No, it's not too late. The goal is to prevent the signal from reaching the TV. It is possible to use filters to remove an offending signal, provided it's not on the same frequency as the desired signal. In the case of that taxi radio on 165 MHz, it's likely causing overload in the receiver. The "stub" filter mentioned in that link is tuned to provide a short on the interfering frequency, which will keep it from overloading the receiver. The biggest issue with stub filters, such as the one in that link, is they work on odd harmonics of the desired frequency as well. This could cause problems on 495 & 825 MHz as well. So, it might cause a problem with stations in the vicinity of Ch 18 or (no longer used) Ch 73.

[ota_canuck]

One of the other most common 2way radio type interferences is from trucker's CB radio use while they're sitting in the factory parking lot across the street. As you said, with the taxi radio on 165 MHz issues, the CB's are likely also causing overload in the receiver which can affect most, or all of the TV 7-51 signals. CB radio interferences can be extreme, if the user does not have their CB antenna trimmed out properly, then they will really make a mess of local TV reception.

[JamesK]

^^^^
If a CB is causing that sort of interference, it's running a lot more than the permitted power level. Those radios are allowed a maximum of 5 watts DC input power or 4 watts RF output. Also, the most likely channel to be interfered with is Ch 2 (2nd harmonic of 27 MHz).

[pr92]

I never heard it, because they got cable by the time I was old enough to care, but my grandmother said she used to be able to hear truckers talking through her TV when they would pass by. This was obviously in the analog days.