This question was triggered by a couple of 'issues' I experienced some years ago. We no longer call them 'problems'. But INTERFERENCE is a huge issue and increasing in trouble level every day!
This is in no way an exam question as it is not a multiple choice answer.
I would like you to think about the 'mechanism' of this interference question.
A Radio Amateur in Gauteng has an H.F. transceiver putting out 400 Watts and a beam antenna pointing north towards Zimbabwe.
His neighbour next to his property is to his north and is listening to 702 on VHF FM on 106 MHz.
The ham has a sked with his friend in Zimbabwe on 10 metres. They have chosen to use 28.200 MHz.
After a few minutes of transmitting, his neighbour shouts at him over the fence. "You are wiping out my 702!"
He ignores him and they switch to narrowband FM on 28.2MHz. (Check the IARU Region 1 Band plan.)
The neighbour now goes to his garage and gets a loudhailer. Shouting "Now I can hear you plain as day!"
[There are various points here that should give you pause for thought.]
Questions
Explain the mechanism using simple maths and the knowledge from previous lessons.
Who is at fault? Or What is at fault?
What should the Radio Amateur do?
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28000 - 28070 200 CW 28055 kHz - QRS Centre of Activity
28060 kHz - QRP Centre of Activity
28070 - 28120 500 Narrow band modes Digimodes 28120 - 28150 500 Narrow band modes Digimodes, automatically controlled data stations (unattended)
28150 - 28190 500 Narrow band modes
28190 - 28199 International Beacon Project Regional time shared beacons, exclusively
28199 - 28201 International Beacon Project Worldwide time shared beacons, exclusively
28201 - 28225 International Beacon Project Continuous duty beacons, exclusively
28225 - 28300 2700 All modes Beacons
28300 - 28320 2700 All modes Digimodes, automatically controlled data stations (unattended)
28320 - 29000 2700 All modes
28330 kHz - Digital Voice Centre of Activity
28360 kHz - SSB QRP Centre of Activity
28680 kHz - Image Centre of Activity
29000 - 29100 6000 All modes 29100 - 29200 6000 All modes FM simplex - 10 kHz channels
29200 - 29300 6000 All modes Digimodes, automatically controlled data stations (unattended)
29300 - 29510 6000 Satellite Links 29520 - 29590 6000 All modes FM-Repeater input (RH1 - RH8)
29510 - 29520 Guard Channel
29600 6000 All modes FM Calling channel
29610 6000 All modes FM Simplex-Repeater (parrot, input + output)
29620 - 29700 6000 All modes FM-Repeater output (RH1-RH8)
This is the HF Region 1 'bandplan'. Remember it is only a plan or recommendation.
So your decisions as to who is at fault, may or may not be 'legal'.
[I didn't intend for this to complicate the question.]
The 'thinking' about the process of interference is what I am after. Enjoy the puzzle.
Don't just go to the following pages. Understand the question first. Try and work out the means of the interference to the FM VHF radio.
73 John ZS6WL
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