[Elecraft] K2/XV144 Power Overshoot

[Glenn McNeil]

Hi Gang,

I've got a problem with my K2/XV144 combination when using a Linear 
after the XV144. I've setup the combination correctly ( I think) and it 
works fine barefoot...max power of 5w from the K2 to drive the XV144 
easily gives me 25w plus out on 144 Mhz

As soon as I hook up my 4CX800 Linear, things get hairy. I have reduced 
the K2 output to likewise reduce the XV144 output to accomodate the 
drive requirement of the Linear ( around 4w at 144 ). Fault tripping has 
been tolerable up until now, using a common 144 Mhz Antenna port. 
However, I have just split Tx/Rx on 144 to allow me to use an LNA 
Technologies Cavity preamp ( which works very well by the way ). The 
Linear now trips off constantly. I did have this problem before, but I 
managed to cure it by reducing the K2 drive to the XV144 and likewise 
reducing the XV144 output. Now it sees that I have got slightly more 
output from the XV144, as I no longer have the Tx/Rx Relay losses. The 
amp trips continually.

The root of the problem appears to be that the K2/XV144 combination does 
not hold set power very well at initial keyup...a burst of higher power 
is seen on the wattmeter, followed by the K2/XV144 quickly reducing to 
set power. This was/is a common problem on some Japanese plastic boxes. 
I have tried all manner of power combination fiddling, but I can still 
see a significant " burp" on keyup...enough to trip the Amp off.

Interestingly, this does not seem to be evident if you use the low power 
transverter drive...I'm using the Hi Power drive, out of the existing K2 
RF Connector. I have an XV50 and XV144 daisy chained on this port ( and 
hopefully an XV432 shortly ), and a Kuhne TR1296 on the low power split 
ports that are part of the 60m Option. I would run the whole lot off the 
low power port but the TR1296 does not get on all that well with the XV 
Transverters. It is not isolated when not in use RF wise, and attaching 
it to the Tx/Rx Transverter drive lines affects things...for the worse, 
as it loads down the system. I could of course, relay isolate the TR1296 
in a similar fashion to the XV units...but thats a  lot of mucking around.

Is there any way to cure the power overshoot on intitial keyup when 
using the standard RF Antenna Port output to drive XV Transverters...has 
anyone else seen this effect, or do I perhaps have a fault ? The problem 
appears to be in the K2, and the XV144 just follows suit. I was going to 
take the cowards way out and put a 3db power attenuator in the RF feed 
from the XV144 to the Linear to try to calm things down..but I don't own 
one, so would have to purchase one...more dollars !

Any ideas ?

73
Glenn
VK4TZL



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