12m SWR issues

[w0mu]

I was doing some checks on my bandpass filters last night and noticed
the the swr on 12m is 1.5 or 1.6 :1  this is into a dummy load.  All the
other bands read 1:1 as expected.  Could this be just a meter anomaly or
is something possibly amiss in the radio?

--
Mike W0MU

J6/W0MU November 21 - December 1 2011 CQ WW DX CW
W0MU-1 CC Cluster w0mu.net

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[VK7JB]

Hi Mike,

Do you have the KAT3 installed?  If so, the "fix" may be simple: take the ATU out of bypass mode and tune the ATU into the dummy load once on each band.  You might then find that with the ATU bypassed, the SWR shown on the K3 meter reads 1.0 as you'd expect.

I noticed the same on 10 & 12m some time ago on my new K3.  I learnt that the ATU is not physically removed from the circuit in bypass mode, but small values of L & C are inserted to electrically / functionally "bypass" it.  Stray reactances can cause these small SWR anomolies on the higher bands, seen when transmitting into a dummy load with the ATU bypassed.  It seemed to me that the ATU can compensate for these reactances if it's tuned once into a 50ohm dummy load on the band of interest - that seems to allow the K3 set the bypass state correctly, compensating for the small strays.

At least, it worked for me and a couple of others who'd noticed the same thing and who found this worked for them. I received a few pm's about this after I posted about this to the group some while ago - I guess it will still be in the archive.

Hope that helps,

73,
John
VK7JB