Hello Jim,
Nice to hear from you again.
I did not make a common mode feedline choke for the amp that would have 5kOhm Z
as K9YC recommends. I did make a common mode choke for the switchmode power
supply AC line. The PS was producing some “squggles” on 137 kHz. 6T on the
largest FairRite #31 snap-on core eliminated that. Enough turns and enough of
those cores should get you to 5K Ohm on 475 kHz but I have not calculated it.
Perhaps the info is in K9YC’s article.
The transmission line balun that I made for the amp, as mentioned in a previous
post, was 5T of bifilar wire around an unknown (grey) toroid that resulted in
250 Ohm inductive reactance on 137 kHz. When this balun did not help the
distortion I removed it.
Have I answered your question?
Are you planning on getting QRV on LF/MF?
73,
Roger
> On Jun 4, 2018, at 5:15 AM, Jim Thomson <jim.thom@telus.net> wrote:
>
> Date: Sat, 2 Jun 2018 13:37:22 -0700
> From: Jim Brown <jim@audiosystemsgroup.com>
> To: Amps Amps <amps@contesting.com>
> Subject: Re: [Amps] new 2200m/630m amplifier - distorted waveform
>
> <WRONG -- again, it depends on what you mean by the word "balun," which
> <is used to describe at least ten very different things.? A properly
> designed common mode choke wound on a ferrite core, commonly called a
> "current balun," SHOULD be VERY frequency sensitive, in that it should
> present a very high resistive impedance at the frequency of interest. To
> accomplish that, the number of turns and the core material must be
> carefully chosen to put the self resonance at the frequency of
> interest.? I've recently studied and found suitable designs for the new
> 480 kHz band, but not for 137 kHz.
>
> <73, Jim K9YC
>
> ## Ok, Ill bite. How did you cook up a CM choke for use at 475 khz ?
> Like with at least 5 k ohms of RS...and RS > XS.
>
> ## At 1st glance, type 77 might work.
>
> Jim VE7RF
>
>
>
>
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