Tod, That's a nice write-up! I've also used the Spectrum analyser / tracking generator approach - I find the real-time plot instructive for seeing how the SRF swings around with changed lead "dressin
Jim, That's a gracious comment, and I genuinely appreciate it - thank you! But I wouldn't want Dean or anyone else thinking that I was that clever :) I was never considering differential dissipation
Ian, Yes, when the choke reactance and the CM path reactance have the same sign there's a bonus. But what I was actually trying to show in that analysis is that the CM path reactance may have an uppe
Ian, I'll have one last try to get my point across, then I'll admit defeat :) Yes, you have been consistent in saying that "only the choke's resistance is completely DEPENDABLE" for solving RFI probl
I just started making measurements on some CM chokes using Fair-Rite's Here is a typical result: http://www.karinya.net/g3txq/temp/52_mix.png 73, Steve G3TXQ _________________________________________
Bob, Fair-Rite refer to it as a "new" material in the September 2009 copy of their catalogue. In terms of Initial Permeability it sits between Type K material. It doesn't have sufficient permeability
Jim's comment should not be misunderstood. A 1:1 choke balun feeding a _perfectly_ balanced load does not have zero common-mode voltage across it; the choke CM voltage will be exactly half the voltag
Jim, You'll not be surprised that I disagree strongly: 1) It is a BalUn - it's a device that interfaces a BALanced load (the antenna) to an Unbalanced source (radio + coax) 2) If the load is complete
Roger, I challenge a couple of those comments: 73, Steve G3TXQ _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contest
Jim, I'm not going to waste my time in long debate with you again! I'll just leave other readers to check what I have said using NEC. You might believe that NEC can't model the common-mode currents,
For anyone without access to a modelling tool, let me try to give you a simple qualitative analysis. Say we have a perfectly symmetrical dipole fed with coax that drops away exactly at right angles f
Roger, Take a look at the 1:1 Guanella current balun - it's identical to one of Jim's CM chokes. It achieves current balance by impeding common-mode currents. They are the same thing! 73, Steve G3TXQ
For those who still have an open mind on whether or not antenna system balance guarantees zero voltage across the CM choke, I've sketched an equivalent circuit showing various currents, voltages and
"A radiating coaxial cable can be modeled quite well with a combination of transmission line model and a wire. The transmission line model represents the inside of the coax, and the wire represents t
Not sure what your feedline length and type are, but just 2dB of loss in that line would give you a 4.5:1 SWR at the shack end if it were left completely unterminated at the other end. Steve G3TXQ __
I just tried it on an EZNEC model of a 5-el Yagi. The Forward Gain dropped by 0.3dB. The rearward pattern was badly affected: all the nulls were "filled in" as Jim suggested, and rearward lobes were
Ham radio magazine May 1979, and the mobile reference antenna was a Hy-Gain TH-2 tribander Yagi not a Quad. Steve G3TXQ On 17/10/2012 15:29, Big Don wrote: Guess we weren't clear on the methodology.
You can just fit 17 turns of RG-58 on a FT240-31 toroid, and that will give you over 8000 Ohms CM impedance on 160m Steve G3TXQ On 20/10/2012 16:56, Jim Lux wrote: On 10/20/12 8:47 AM, Cqtestk4xs@aol
Jim, That's correct - you have to plan ahead ;) Steve G3TXQ I'll bet that's not with the connector on the coax<grin> _______________________________________________ __________________________________
Roger, Interesting question! I just tried a measurement using four FT240-31 cores - all I had spare in the component draw. I wound 9 turns of RG-400 on a stack of four cores. The CM impedance peaked