[Amps] new 2200m/630m amplifier - distorted waveform

[Roger Graves]

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 at telus.net> wrote:
> 
> Date: Sat, 2 Jun 2018 13:37:22 -0700
> From: Jim Brown <jim at audiosystemsgroup.com>
> To: Amps Amps <amps at 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
> 
> 
> 
> 
> _______________________________________________
> Amps mailing list
> Amps at contesting.com
> http://lists.contesting.com/mailman/listinfo/amps