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CMC-VHF-UHF

Has anyone done any work on VHF/UHF CMCs. power level 25W or so, rather than megawatt monster HF CMCs?

There seems to be a lack of info on such items and on realistic power level [ie, 100W] HF CMC

73
John G8JMB

Generally, a few clamp-on ferrites of the appropriate material at the
feedlint is all you really need. In that respect, even those ferrites
aimed at EMC and RFI control are good for that purpose at VHF/UHF
frequencies. The first KLM 2-meter beam I had I some 40 years ago I built
and installed a 1/4-wavelength 'bazooka' balun. It worked fine, but the
clamp-on ferrites are a whole bunch easier to install. On 70 cm I have
used the 1/2-wavelength coaxial 4:1 balun. The subject is treated in any
good reference addressing antennas and transmission lines at VHF,UHF.

Dave - W?LEV

On Wed, Jan 27, 2021 at 5:13 PM John Button G8JMB via groups.io
<hornpipe112@...> wrote:

CMC-VHF-UHF

Has anyone done any work on VHF/UHF CMCs. power level 25W or so, rather
than megawatt monster HF CMCs?

There seems to be a lack of info on such items and on realistic power
level [ie, 100W] HF CMC

73
John G8JMB

--
*Dave - W?LEV*
*Just Let Darwin Work*

Dave - W?LEV

<<Generally, a few clamp-on ferrites of the appropriate material at the feedlint is all you really need. ..ferrites aimed at EMC and RFI control are good for that purpose at VHF/UHF frequencies

Unfortunately the Z of clamp-ons is a couple of hundred R at best; I'm looking for > 10 times that, eg for resonant feedline and end fed 1/2 wave antennae. So clamp on are inadequate

I should have said that I need broadband suppression, so 1/4 and 1/2 wave types are no use.

73
John

.

John,

if you want to get, say, 3000? choking impedance on UHF, broadband, I can only wish you good luck! Because at 3000? at 500MHz is what a 0.1pF stray capacitance has. So forget about winding multiple turns on a core.

The best thing you ca do, I think, is find out which beads or toroids provide the highest impedance per length over the frequency range you need, and stack as many of them as necessary on your transmission line.

Manfred