All these things have harmonics which can go all the way up to the VHF band and beyond. The fundamental frequency is barely relevant.
However, interference is a separate issue from having simply poor audio performance. I am currently trying to solve this which most people would definitely classify under “poor audio”. It isn’t a serious issue when flying (basically because most ATC / aircraft audio is of barely usable quality 
) but it is irritating when one is trying to sort out a decent sound track for a movie.
Don’t forget ADSL/VDSL (where it is delivered by overhead phone lines) when it comes to noise. Fibre to the premesis can’t come soon enough here; VDSL makes all the HF amateur bands so noisy I can only use them for digital modes.
If your router shows the spectrum of the VDSL signal like mine does, you’ll notice it goes from a few kHz up to about 7MHz (at least mine does, my phone line is underground, but some of my neighbours have theirs delivered from a pole). VDSL/ADSL delivered over ancient copper of dubious origin from a telephone pole may also be a source of noise for your long wave radio.
Capitaine wrote:
The biggest source of the interference was the plug-in power supplies for the internet router and cordless phone: might try putting some shielding around these.
Switched mode power supplies like the ones you mention or in computers, etc. often operate at switching frequencies between 50 and 150 kHz (sometimes even higher up to 500kHz). That happens to be exactly in the spectrum of long wave radio.
Not really aviation, but… I have a 1950s valve radio at home for occasional long wave (Radio 4 or France Inter). It used to struggle with interference, which I tracked down to the power cable, so I re-wired it with some CY shielded cable which made a considerable difference. I also tried a ferrite, a discrete earth connection, and a large external aerial, but to surprisingly little effect. The biggest source of the interference was the plug-in power supplies for the internet router and cordless phone: might try putting some shielding around these.
I fly a plane with an unshielded intercom and after a while the background noise gets annoying (transponder, anticol, nav lights, alternator), so can sympathise.
as you’re using the same grounding from where the interference is coming from!
Not sure I agree with that being the reason why it works 
No need to ground the tape to airframe, because if you do that, you’re basically making the tape useless, as you’re using the same grounding from where the interference is coming from!
the tape has like a metal mesh in it, so you isolate the wiring in a sort of cage.
There is some light tape available, its like high speed tape but with mesh in it. Below is the link of what I’m referring to.. Its the same tape we use to shield Airbus wiring terminations.
That would be an impressive solution indeed!
Presumably you would connect the tape to the airframe.
Some of those tapes are quite heavy.
Best thing to do to all the audio wiring, including wiring going to the jack plugs is to wrap the harnesses in insulating shield, like EMI (electromagnetic interference) tape. I had an issue with 2 Tecnams which had the wiring passing close to a power cable and by doing this, it solved all background noise coming from the alternator.
The rest of the power,data wiring can stay out of the insulating shield
Thanks for all the useful replies, I’ve noted the main points of each post and will check them off the tech who is making my harness and then with the guys installing it.
