AmateurRadio.com

Mike at the EMC compliance test lab I worked at we always used Fair rite products. They helped most anyone that had problems passing the compliance requirements. Good stuff those Snap-on fair rite chokes! The mix determines the frequency of maximum attenuation. Look up a fair rite mix vs freq. sheet when you find where your problems are. Call me sometime and I’ll give you some trouble shooting tips I’ve found. (940) 390 3644 KB5UKT Mike

Having helped others to resolve transmit RFI issues for others – and occasionally for myself – the most common issue is that the feedline and, by extension, the radio itself – and everything connected to it (including the house by way of the power cord) becomes part of the antenna. Remember: Any coaxial transmission line has THREE separate conductors: The inner conductor, the inside of the shield and the outside of the shield – and it is currents flowing on the outside of the shield that are usually the problem for both transmit and receive.

It’s bad enough that in this situation, RF energy from noisy electrical devices *will* find its way back and into your antenna on the outside of the shield and degrade your receive performance, but it’s doubly bad that as part of your antenna, the circulating RF will likely play havoc with things in the shack – namely computer speakers, USB-connected devices, accessories like keyers and other devices within the house. In that case it’s likely that these problems are related not as much from the RF being picked up by the device, but simply reacting to the RF energy being conducted into the house via the feedline.

A common-mode choke on the feedline *at* the antenna is the first line of defense – and maybe another just prior to it entering the shack, *before* any coax grounding or lightning protection can offer significant improvement to both transmit and receive: 8-12 turns of small-diameter (RG-316) coax on a FT240 mix 31 or 43 toroid is a reasonably good performer across HF – with mix 43 being preferred for the higher bands (e.g. 20 meters and higher).

If ingress via the coax has been resolved and there are still issues, point-of-use ferrites on the affected devices is certainly appropriate. With *any* ferrite device – whether toroids or clamp-ons, getting as many turns through it as possible is the key: A single “turn” through the ferrite will likely have only marginal effect at HF frequencies as the doubling of turns generally results in the quadrupling of choking impedance.

As for “noisy” devices that emit HF RF via the mains power connection, it’s pretty rare that simply installing a ferrite device will “solve” the problem: At best one may experience an S-unit or two – but this often does not attenuate the QRM to extinction if the interference is strong. In such cases the addition of an L/C-based mains filter – which includes capacitors as well as inductors – that is bonded to the metal chassis of the offending device is called for. With appropriate attention to detail I’ve been able to quash interference from such devices to the point of undetectability.

73 and good luck!

Thanks for this information. Is there any listing that lists which mix of ferrite to use and where? I’ve tried all sorts of mixes with varying results and at different frequencies. A list of the mix and where to use from hams with more experience with these things would really help.

73,
Phil
K7TTI

Thanks for that link Mike. I have purchased from Palomar before but never dilled deep enough down into their website for this type of information all in one place.
It’ll be useful for sure.

73
Phil
K7TTI

Fair-Rite does have a YouTube channel, and the single topic episodes are not very long. https://www.youtube.com/@FairRiteProductsCorp