[Amps] RF in the Audio

Fuqua, Bill L wlfuqu00 at uky.edu
Sat Sep 24 13:39:41 PDT 2011

while you are at it show me an ideal "common mode choke" or BALUN.
Bill wa4lav

From: amps-bounces at contesting.com [amps-bounces at contesting.com] On Behalf Of Jeff Blaine [keepwalking188 at yahoo.com]
Sent: Saturday, September 24, 2011 3:17 PM
To: Rob Atkinson; amps at contesting.com
Subject: Re: [Amps] RF in the Audio


If you would agree that "balanced" feeds are never idea, then a common mode choke is going to be of benefit.

And when you find one of those ideal balanced feed lines, let me know.  I could use some here myself.

73, Jeff ACØC

-----Original Message-----
From: Rob Atkinson
Sent: Saturday, September 24, 2011 2:07 PM
To: amps at contesting.com
Subject: Re: [Amps] RF in the Audio

>You may not have heard about the concept, but it works quite well. DX
>Engineering has done similar things, but don't publish it.  I've done
>considerable work on the topic, and published both the theoretical basis
>and the measured data. Since I've done that in the tutorial, and because
>this reflector is about power amps, I won't repeat the discussion. If
>you open up some of their boxes you can see what they're doing.

I may have missed something but I was unable to find any sort of
common mode choke on the DX Engineering website, designed to be
inserted in a near or perfectly balanced parallel wire feedline.

I am reasonably certain that such a device would introduce an
impedance bump that would not perform favorably under continuous duty
power, given the wide range of reactances, and varying locations of
current and voltage maxima occurring with use of a single balanced
antenna on all HF amateur bands.

I am certainly willing to stand corrected, but at this point, i do not
see anything in your pdf paper, and unpublished DX Engineering work,
whatever it might be, are unpersuasive, compared to a test of say, a
1500 watt 7 MHz RTTY transmission through such a choke, inserted
between a balanced matching network and a half wave 80 m. center fed
dipole.  I wish to note that your pdf paper seems to be coherent and
useful in other areas and I am questioning this one point.

If you can perform such a test, with a field strength measurement
taken without the choke, followed by one taken with the choke in line,
with no other variables of course, and an ambient temperature
measurement of the choke, and another one near the end of the 10
minute test transmission, and show little or no difference in field
strengths and little or no temperature rise, I might be willing to
reject my intuitive doubts.

This is somewhat relevant to the amps reflector because while it has
to do with feedlines, I for one, think of feedline components in terms
of QRO and continuous duty, and one way we get QRO is with RF power

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