Someone said; "It all goes away with load shedding!" - Yes the neighbour might not have a battery operated radio...
Potential Answer
I assume that the Ham radio operator has very good equipment, operates legally and is licenced. Could it be that the radio of the neighbour gets over loaded with spurious products from the radio's intermodulation distortion from the mixer; that could interfere with the neighbour's radio reception?
He could add additional filtering before his radio receiver that could remove the strong signals that overloads the radio receiver. I would say, add a high pass filter because the Ham operator transmits at HF 28MHz and the neighbour is listening on VHF 106MHz.
My response was:-
Yes almost right. You are not far off it. Remember the ham has a beam pointing North. Over the garden wall... Right at the neighbours house. And then think about 'image rejection'.
Noise has little to do with this 'interference' complaint. 'Cheap' FM radio/lo-fi and overloaded front end. Remember FM radios are local oscillator on the lower frequency side. They cannot be on the high side as the local oscillator would be in the aircraft bands.
Later
First of all think about the 3rd harmonic of 28.2 MHz. Then think about a 'low cost' FM radio having poor image rejection - second channel. The intermediate frequency of 10.7 MHz, means that the image is 21.4 MHz away from 702's Pretoria transmitter on 106 MHz...
You might need to reread the question. The Radio Amateur is using a recently bought transceiver that complies with the regulations. A beam that also is professionally made with only 400 Watts of output.
10.7 MHz is a global standard for an FM broadcast radio.
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If you have a so called hi-fi tuner, you will probably have one with a plastic housing. No screening to speak of whatsoever.
Most Radio Amateurs will tell you to have a high-pass filter inserted in the antenna coax. To suppress the HF transmission. This will be of little use as the signal (Now around at Volts/metre) will bypass the filter and impact the tuner's front end directly. (screening of the receiver)
I picked 28.2 as an example frequency because I could remember 702 from the Pretoria transmitter is on 106 MHz. So the 'image frequency' would be 106 - 21.4. That is 84.6 MHz. The third harmonic of 28.2 MHz. This example also applies to the fifth harmonic. Which works out to be 16.92 MHz and is well out of band. So unlikely to be an issue! But the fourth harmonic would be 21.15 MHz. Another possibility. These harmonics would not be from the amateur's transceiver. But would be generated by the 'front end' circuits in the radio receiver. All of this can be summarised as a 'failing of the receiver'.
On this weekend I tried my phone's VHF FM radio. When I scanned the band, it found 47 radio stations here in Roodekrans! So the potential for interference is high. Also - as can be seen by the cartoon - the Radio Amateur will get the blame.
So whilst the radio receiver is technically at fault, try explaining that to your neighbour!
The radio amateur should first of all have a LOG of all his transmissions. So that he can refute claims of interference by referring to his LOG's time and date and frequency.
Secondly he should not be transmitting a full 400 Watts into a beam antenna. Especially on 10 Metres. When the band 'opens', the power level can be reduced to below 50 Watts or even 10 Watts.
Thirdly the radio amateur should offer to assist in solving the 'issue' with his neighbour. With a proviso that he doesn't spend money or a great amount of time. Some 'issues' could take some solving!
One solution that occurred to me was that the coax down lead to the radio receiver might be picking up more energy at HF than the front end could handle. Therefore a "Braid-Breaker" might resolve the 'issue'. So some experimentation would be needed. After all a recent anecdote had a plasma television wiping out HF for a nearby amateur! The coax to the roof antenna was resonant at 40 metres!
From a very old QST magazine.
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