Why use 9913 to make chokes when smaller diameter PTFE cables are
available? At 30Mhz, RG's 142 (3Kw), 223, 304(6Kw), all handle max
legal power plus with some VSWR headroom, and 316(1Kw @ 30Mhz, 2.26Kw @
7Mhz) for lower frequencies and power levels. (RG213 is 2Kw at 30Mhz).
It seems to me that the smaller braid OD has less capacitance per turn,
assuming they are spread out around the core. Or at the same self
resonant frequency get more choke Z with a few more turns - N squared
sure helps. Even at a couple of bucks per foot, only need a few feet
are needed. You might have one more coax to coax connection up in the
air and lose another 0.05db , which is a little downside.
Times Microwave has their full coax catalog pdf at
They also have a nice loss/power on-line calculator at
Jim Thomson wrote:
> For 50 MHz, you want two or three turns through a 1-inch long core and
> two turns through a 2-inch core,. and for maximum noise suppression, you
> will want at least three of these multi-turn chokes in series along the
> line, close to the feedpoint. The reason you need multiple chokes in
> series is that you only need 2-3 turns to put the resonance at 50 MHz,
> so you haven't got much benefit from N-squared. Fair-Rite #43 and #31
> are roughly equivalent at 50 MHz.
> 73, Jim K9YC
> ## what do u mean by a 1" long core ? Does this mean 2.4" OD x 1/2"
> torroids used... and 2 of em stacked ? Is a 2 " core consist of 4 x
> torroids ?
> ## It can't be ID. You won't fit 9913 through a 1" ID very easily..well
> maybe u can?
> How far apart is each of the 3 x chokes to be spaced from each other ?
> How do u
> propose to keep this mess away from the boom..and or mast ?? I think I
> would want
> all of them to be at least one outer loop diam away from metal. If they
> are touching
> metal, the C between coax braid and boom/mast/tower will surely screw up
> the chokes ?
> You would end up lowering their resonant freq. The stray C would parallel
> resonate the
> chokes..and probably increase the choking Z... but at a lower freq. It
> might be broad enough
> peak to still cover 6m.
> ## In some cases, you can't hang em below a boom...if the connections are on
> top of the boom.
> Even if hung below a boom, I would not want them flapping in the breeze.
> What's the fix ?
> Jim VE7RF
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