Topband: cutting coax stubs for 80 meter 4-square

Jim Thomson jim.thom at telus.net
Mon Jun 11 12:50:36 EDT 2018


Date: Mon, 11 Jun 2018 07:29:39 -0700
From: "Richard (Rick) Karlquist" <richard at karlquist.com>
To: terry burge <ki7m at comcast.net>, topband at contesting.com
Subject: Re: Topband: cutting coax stubs for 80 meter 4-square

On 6/10/2018 8:01 PM, terry burge wrote:
> All's well that ends well I'm happy to report. K2AV, Guy suggested I check the SO-239 on the Rig Experts AA-170 and I found an open solder joint between the back of the connector and the circuit board. Even with my close in glasses and a magnifying glass it was hard to be certain. So a little solder and 'hop-a-long' rides again! It's working. Will check out the coax stub again to see what the RE reads now.
> Terry
> KI7M

<My AA-55 is a different model than yours, but the instructions
have curious warning about not putting too much force on the
UHF connector.  I am thinking that RE realizes they have a
weak mechanical mounting, relying on solder.  I think I will
revise my advice:

1.  Always use a DC block
2.  Carefully attach a short flexible coax jumper and leave
in place.  Calibrate it out.  Then connect the DUT to the
end of the jumper.  No mechanical stress on the UHF.

Rick N6RK

##  Is there room inside those  rig experts units to install a .01 uf disc ceramic  cap ?? 
A  50-100  volt  cap would be smaller diameter than a 1 kv  cap.   There is  your  DC
blocking right there.  .01uf  = 10,000  PF..which  is ample.  .01uf  = just  8.846 ohms of  XC
on  1.8 mhz...and  WAY less Xc, when on higher freqs.... like 4 ohms on 80m..and  2 ohms on 40m. 
If a .02 uf cap was used, the XC  would be half again.    

## On a similar note,  re the MFJ-259B.   Can  a HP filter be used, to kill  AM broadcast
junk...or  will the HP filter  screw things up too much ?  

Jim  VE7RF




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