[Elecraft] K3: internal 2m transverter offset problem

[Edward R Cole]

Jim,

First the XG3 is not exact on frequency.  I use a very good counter 
which will read up to 26-GHz and has an internal TCXO.  I've noted 
the XG3 being off up to several tens of Hz, so to use as a frequency 
std is not sufficient for measuring EXREF frequency accuracy.  Its 
pretty good for its intended use as signal source.

But 5-KHz is quite a lot for 2m.  Frequency accuracy is the sum of 
the K3 error and transverter LO.  Most often I find the transverter 
that uses a xtal LO can be quite far off frequency.  You pretty much 
need a frequency counter to read this (if IF is 28-MHz, then LO is 
116-MHz).  At present my 2m transverter LO is low by 50-Hz since I 
have not adjusted it for some time.  Originally, I had it within +5 
Hz.  I recently fixed my EXREF in the K3 and its within 1-Hz at 28-MHz.

But sometime during the time my EXREF was not working*, I entered a 
fixed offset for the transverter in the k3 CONFIG: XV1 OFS.  I was 
wondering why my frequency was off 22-Hz after fixing the EXREF.  I 
had to disable EXREF to reset the offset to zero.  Then after 
reentering EXREF my 28-MHz frequency was within 1-Hz (after 15-min 
warm up).  Your REF CAL looks normal for running EXREF after warm 
up.  The TCXO will drift as it warms up resulting in the EXREF 
correction.  You should not see much change once the K3 is fully warmed up.

Using a transverter+K3 as frequency meter is not very conclusive if 
you have not checked it with an accurate counter. Most VHF radios and 
HF+VHF transverters will be off frequency at VHF unless one has 
checked with an accurate frequency counter.  Usually I see up to 
100-Hz of error from other VHF stations.  Makes it fun running the 
RIT during a 2m SSB net.  Have you measured the K3 frequency at 
IF?  I will guess the error is in the transverter LO.

You can check the K3 against 15-MHz WWV.

73, Ed - KL7UW
*EXREF quit because of a loose sma connector from the 10-MHz source.

Date: Tue, 3 May 2016 14:03:23 -0400
From: "Jim Spears" <n1nk at cox.net>
To: <elecraft at mailman.qth.net>
Cc: <n1nk at cox.net>
Subject: [Elecraft] K3:  internal 2m transverter offset problem
Message-ID: <000501d1a566$1580b9e0$40822da0$@net>
Content-Type: text/plain;       charset="us-ascii"

I have K3 s/n 6866 with internal 2m transverter.  I have not paid much
attention to the transverter for a while but I noticed something odd a
couple days ago and have not been able to do anything about it.



If I set the Elecraft XG3 to 144.100 and feed its output into the
transverter input connector, the signal shows up at 144.095, 5 KHz low.



If I tell this K3 to output 2m rf on 144.100, I hear the signal at 144.015
on K3 s/n 6425 which has an external 2m transverter.



I first noticed this when monitoring a local 2m FM repeater and could not
copy its output until I tuned 5 KHz low.



The K3 does have an external 10 MHz clock and CONFIG REF CAL has the
blinking asterisk.  FWIW, the value shown is 49.379.962.



CONFIG XV OFS is 144  -0.08 and cannot be changed, when I go to adjust it
REFLOCK appears.



What's up Doc?



Jim/N1NK





73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com