[R-390] the saga cont. pt 9

[William A Kulze]

I've got some 90° adapters, SO-239 to the twinaxe. They don't seem to have anything inside, just grounds one side of twinaxe, like recommended for feeding twinaxe input in the R390a info out there. Now, I've always heard that if you don't use the balanced input you're skipping a stage of preselection that will null any unbalanced noise that may be on the balanced line.  How's all this work if you're connecting 50ohm coax to the balanced input? If you feed your Sig Gen to the junction of two 68ohm resistors at the balanced input to make the adjustment, are you still going to see any improvement if you ground one side and feed with coax?

Bill W2NVD



-----Original Message-----
From: r-390-bounces at mailman.qth.net [mailto:r-390-bounces at mailman.qth.net] On Behalf Of rbethman
Sent: Monday, September 20, 2010 2:19 PM
To: r-390 at mailman.qth.net
Subject: Re: [R-390] the saga cont. pt 9

  The "Twinax" connection was meant for something around 120 to 150 ohms 
for Z.

It really doesn't matter unless you have a way to alter the impedance of 
the signal generator!

These were originally aligned with the AN/URM-25(X) series of signal 
generators.  They came with a "dummy" antenna of 50Ohms Z.

If you perform the alignment with a 50 Ohm Z signal output, then you are 
going to be in a "better" position, since today's antenna systems are 
"normally" a feed impedance of 50 ohms.

Tweak and peak accordingly!

Forget the "twinax", and use the "C" connector next to it.  It was meant 
for 50 ohms Z.

Bob - N0DGN

On 9/20/2010 2:01 PM, ka9egw at britewerkz.com wrote:
> What fun...got my Amphenol 82-5628 BNC-to-Twinax adapter in the mail
> today...it doesn't seem to work very well; I get better results off the
> unbalanced input and the adapter whows some fraction of an ohm between pins
> and between either pin and ground.  Does anyone know if it has some sort of
> balun or the like in it, and if so, what's the Zo and freq range?
> 73, Brian KA9EGW

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