Date: Thu, 20 Apr 2023 20:30:52 -0700
From: Jim Brown <jim@audiosystemsgroup.com>
To: amps@contesting.com
Cc: Bill Whitlock <engineer_bill@verizon.net>
Subject: Re: [Amps] World's worst coax connectors
<That's something I've never experienced, and I did a LOT of work in
<downtown Chicago! I suspect something else in that interface is causing
<the problem. What frequency was the RF? Were all the cables twisted
<pair? What was the nature of the shield? Foil with drain, or copper braid?
<I'm copying Bill on this.
<73, Jim
On the back end of all my Neutrik XLR connectors, there is 4 pins. The 4th
pin is internally bonded to the shell of the XLR. I bond pin1 to pin4.
on all the xlr connectors, female and male. Then when plugged into
various pieces of rack gear, pin 1 is now bonded to the chassis of that
piece of rack gear..... problem solved...even if it doesn't meet some spec.
ALL of my XLR cables I fabricated myself, were 1 pair, twisted, and teflon
insulated..and a woven braid, then the outer pvc sheath...(surplus telco
cable we tossed at work). I also wired a small, 500 pf @ 25 vdc disc
ceramic cap, between Pin 2 + Pin 4......and also Pin 3 + Pin 4. The caps
were a K6JRF trick that works superb. But these cables I made are all
short, like 18" long, just to go from one unit to the next to the next etc.
On a similar note, APHEX suggested wiring the shield of any cable to pin
1...only at one end of the cable....and I think they said the..'sending
end'. ( I might have that backwards). That was their way to get around
pin 1 issues. I made up just one cable like that..and it too works, but I
don;t like that procedure...esp with a bunch of HF amps sitting mere inches
away.
If that terminating Pin 1 at only one end stunt is used on 1/4 TRS
connectors, the issue then is... IF the cable with the TRS plug on EACH end
is reversed, all hell breaks loose. With XLR connectors, they only
terminate one way, since there is a female on one end..and a male on the
other end.
I don't have any issues with hum, buzz, RFI etc, touch wood. I found I
did have to plug all the rack gear into the same 120 vac outlet.
I avoided those cables that have the foil 'shield'..and the ..'drain wire'
. Next to useless, since the foil is aluminum, and makes for a
lousy..'shield'.
To interface with the xcvr.... I had to use a 20 db balanced pad...then
into a Jensen xfmr... wired balanced on it's input...and UN balanced on
it's output side..then through a 220 uf non polarized cap... then into the
analog balanced modulator chip, on one pin. New RCA connector installed on
back, aluminum rear apron of the yaesu.
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