Coaxial Ferrite Choke

**Archy** · 04-06-2022, 06:37 PM

Mix 31 will cover the lower amateur bands as well as 10/11m. 43 performs better from 10 and up, how high up, I do not know. I know this is vague, but I am not a ham, I'm strictly CB only. I don't even use UHF.
The other reason for #43 in that particular ferrite is availability, #31 is harder to source. Unless the ferrite fairies just delivered some for Mouser. By the way, the price of those has gone up dramatically, I previously bought them for under AU$7. Must be covid and the shipping the container crisis. Look at Element14 instead.
If you want to know how they perform at various frequencies, try YouTube. I believe there are some videos testing baluns and ununs using different mixes. The SWR curve may be directly relative to choking impedance??
The other way to find out is to read the article I was talking about. He did some fairly extensive bench tests, and there's a table on ferrites and windings for each band. The number of windings is frequency dependant, more windings is not better for optimum choking impedance.
I'll dig up that link, it's a must read for all radio operators.

**Archy** · 04-06-2022, 06:43 PM

From page 34 there's the tables. Plenty of graphs to analyse too.
Enjoy the read!
http://www.w9joz.org/RFI-Ham.pdf

**Alabama Buckeye** · 04-09-2022, 06:53 PM

Thanks Archy for the feedback. I too am most interesting in 11M band though I listen to VHF/UHF, for the most part, and 10M as well. I'm GMRS licensed, only need to pay the goobermint do do so, so a smidgen of UHF chatter is exchanged. GMRS license price also sky-rocketed, must be the increased shipping as well.

Anywho, what can anyone tell me about 9:1 Baluns; specifically what sort of antenna are they used with? I'mtrying Utube.com and find no explanation of what a single wire antenna is. I might assume a monopole like a 102" CB whip;
which wouldn't be the first time I'm wrong?

I've seen talk oflong wire antennas where a 9:1 Balun is spoken of meanwhile the Uboob speaker keeps moving the attachment point until finally he's end-feeding the wire and speaking of reaching 1000 ohms or more. What is the 450 ohm antenna that the 9:1 is translating to 50 ohm coax?

**Archy** · 04-09-2022, 08:15 PM

I'm no expert, but I was talking to a bloke in Western Australia just yesterday about this. He was using a 40 odd foot inverted L antenna with a 9:1 voltage balun to a tuner. The antenna also had some ground radials/counterpoise.
9:1 and other ratios are typically used for high impedance end fed wires over a quarter wavelength long. In this guy's case, I think the aim is to step the impedance down to a region that is manageable with an antenna tuner. Also maybe to flatten the SWR curve for multi band use?? It means for a more flexible, usable antenna.
I have watched a YouTube video where they hooked up an analyser to various baluns and ununs. They recommended using a 1:1 current balun in conjunction with a 9:1 or 49:1, the 1:1 being after the voltage balun, radio side.
By the way, the guy in WA was using three of the 43 mix ferrites that I suggested, stacked together for good power handling.

**mjd420nova** · 04-11-2022, 09:32 PM

One trick I learned over the years was that when the coax terminations are made, wrap them with the plastic electrical tape, then apply a coating of silicone around everything. That seals out moisture and a quick slice with a knife to split the tape to remove it, but when done properly, it will last twenty years in the harshest environment. I did hundreds aboard ships that were still intact after thirty when scrapped.