[Elecraft] Cal AT100 SWR bridge

[Geoffrey Mackenzie-Kennedy]

Hi Rich,
Have you tried disconnecting the antenna system and putting a 50 ohm dummy
load at the output of the Daiwa ? If the Daiwa is OK and the tuner's VSWR
bridge is OK  both should give you almost the same readings. I say almost
because the additional connectors and line plus the Daiwa that the tuner
sees between it and the dummy load will make the tuner's load something
other than 50 ohms, unless something in the Daiwa - 16" line combo is
compensating. But the diff should be small, increasing with frequency - but
still small.

If that's OK and you reconnect the antenna system and the problem comes
back, then either the antenna system does not look like 50 ohms resistive at
the "problem frequencies" or you have "antenna currents" on the outside of
the feeder - or both - or some grounding problem. If of any help I would be
glad to discuss symptoms / possible cures off list.

When I did the null adjustment with C31 I also found the null to be shallow
and quite broad. But after moving the one wire primary of T1 so that it
passed through the core dead centre, the null became much deeper and
sharper. KAT100 now gives reasonably correct readings.

Good luck es 73,

Geoff       GM4ESD



----- Original Message ----- 
From: "Rich McCabe" <r.mccabe at 1967z28.com>
To: "Elecraft Reflector" <elecraft at mailman.qth.net>
Sent: Friday, September 24, 2004 4:31 AM
Subject: [Elecraft] Cal AT100 SWR bridge


> Is there any tricks (or improved techniques) on adjusting the SWR bridge
in
> the tuner? I just finished a tuner and everything checked out and
calibrated
> very easy. But I may have a SWR that agrees on my Daiwa in the line 16"
away
> or it may be as high as 4:1 on some bands even when the tuner says it is
> flat or near flat.
>
> I have adjusted C31 for minimum reading (.01 volts) and the null is small
so
> I really cant center it in the null easily.
>
> I also had a problem with oscillations on 40 meters and I think I read
> somewhere it could be a grounding issue. So I am going to go back and do
> some more sanding.
>
> Any tips or comments.
>
> Thanks,
>
> Rich
>