Thankfully, not many people have plasma televisions these days. However, if you are unlucky enough to own one, or a neighbour still owns one, this is what you can expect to see and hear. The radiated RFI will be broadband and may extend from 160m up through the HF bands. It is likely to be worse on the lower bands, but will still render the higher bands somewhat useless for all but very strong signals. The noise source may be located hundreds of metres from your station. Hopefully, it wont be too far away and you’ll be able to use DF techniques to locate its source. The short video illustrates what Plasma TV QRM looks and sounds like.
Credit: KP4MD, YouTube
What can I do to eliminate or suppress this QRM?
Plasma TVs are shocking. The noise is strong and broadband. You may need to trial different methods. Start by reverting to first principles; maintain a log so you can be clear as to when the noise is active and which bands it is impacting. Make a special note if it is also impacting the AM broadcast band (this could help if you need to lodge a complaint with ACMA).
If the television belongs to a neighbour, be sure to read the QRM Guru posts on dealing with neighbours.
1. You can try a Noise Canceller such as the MFJ-1026 or similar. … here is a testimonial from Steve, N4LQ:
“Forget using any kind of line filters. The noise is radiated from the SCREEN….straight out. After months of experimentation, the only cure has been the MFJ-1026 and it works magic! Having a K3 with LP-PAN or P3 makes adjustments easy. Otherwise it would be a real pain to tweak. You do need a decent noise receiving antenna for the 1026. The K3 has the RX-IN/OUT jacks which allows to interface the 1026 with ease and retain your QSK without using the MFJ internal relay.
Contact me for any further info. 73
2. You can try using ferrites to suppress the noise; both at the source and at your station.
There are quite a few posts on this topic on QRM Guru. Read the posts on using ferrites to suppress QRM. As plasma televisions radiate such strong unwanted signals you may need to use big, heavy ferrite rings, or large snap-ons. You’ll want to get the maximum number of turns of the wires and feedlines through the core. Mix 31 may be preferable depending on the frequencies at play, but the cheaper Mix 43 may suffice if the noise is not as intense and/or the frequencies are not too low. For the lower HF and MF bands Mix 31 may be more effective.
If nothing works, newer LED technology televisions have become very affordable and are far less likely to generate unwanted QRM. Offer to go halves in a new television for your neighbour. Worst case, you may need to buy the TV outright; it could be a cheap solution to your problem, and if it gets you back on air, it’s probably worth it.