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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[Dick Hanson-2]

Hi Glenn...

You have done a good job of sleuthing and pondering the various
solutions.

Bottom line is that you may well need to communicate via email with the
boys at Elecraft about this. If they have had other similar reports (or
even if they have not), they will try for a solution. Also, you may well
get a response from other VHFers that have been down this road.

First, I believe you're correct in figuring it is the K2 and not the
transverter.
I have run into exactly the same issue with one of my VHF combos. I have
a Yaesu FT-897 driving a Lunar 2 meter amp (pair of 3CPX800, with very
sensitive grid trip circuitry). Same exact problem. Yaesu tech support
told me how to adjust some of the ALC circuitry to "tune out" or at
least minimize the initial ALC related overshoot.
This helped a lot. Then I "slowed down" the pulse in the grid trip
circuit in the amp by adding slightly more capacitance to one of the
time constant caps. The combination of these two things solved my
problem. I did not try the in-line attenuator approach, but that may be
helpful too. You could easily fashion a 3 db attenuator out of a length
of RG-174 mini coax. It has a healthy amount of "loss" per foot, so you
could quickly calculate how many feet you would need to arrive at 3 db.

I have both the XV-50 and XV-144 now to use with my K2 but have not yet
used them in our VHF contest station with an external amp to observe
whether this phenomenon exists. I will hasten to do some testing and get
back to you on this.

Good luck.
Dick

-----Original Message-----
From: elecraft-bounces+k5and=[hidden email]
[mailto:elecraft-bounces+k5and=[hidden email]] On Behalf
Of Glenn McNeil
Sent: Saturday, May 21, 2005 22:55
To: [hidden email]
Subject: [Elecraft] K2/XV144 Power Overshoot


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[W4sc]

Hmmmmmmm   Maybe the same is causing my "Hi Curr" indication on HF
occasionally.

2577

----- Original Message -----
From: "Dick Hanson" <[hidden email]>
To: "'Glenn McNeil'" <[hidden email]>; <[hidden email]>
Sent: Sunday, May 22, 2005 6:18 AM
Subject: [Elecraft] K2/XV144 Power Overshoot

> Hi Glenn...
>
> You have done a good job of sleuthing and pondering the various
> solutions.
>
> Bottom line is that you may well need to communicate via email with the
> boys at Elecraft about this. If they have had other similar reports (or
> even if they have not), they will try for a solution. Also, you may well
> get a response from other VHFers that have been down this road.
>
> First, I believe you're correct in figuring it is the K2 and not the
> transverter.
> I have run into exactly the same issue with one of my VHF combos. I have
> a Yaesu FT-897 driving a Lunar 2 meter amp (pair of 3CPX800, with very
> sensitive grid trip circuitry). Same exact problem. Yaesu tech support
> told me how to adjust some of the ALC circuitry to "tune out" or at
> least minimize the initial ALC related overshoot.
> This helped a lot. Then I "slowed down" the pulse in the grid trip
> circuit in the amp by adding slightly more capacitance to one of the
> time constant caps. The combination of these two things solved my
> problem. I did not try the in-line attenuator approach, but that may be
> helpful too. You could easily fashion a 3 db attenuator out of a length
> of RG-174 mini coax. It has a healthy amount of "loss" per foot, so you
> could quickly calculate how many feet you would need to arrive at 3 db.
>
> I have both the XV-50 and XV-144 now to use with my K2 but have not yet
> used them in our VHF contest station with an external amp to observe
> whether this phenomenon exists. I will hasten to do some testing and get
> back to you on this.
>
> Good luck.
> Dick
>
> -----Original Message-----
> From: elecraft-bounces+k5and=[hidden email]
> [mailto:elecraft-bounces+k5and=[hidden email]] On Behalf
> Of Glenn McNeil
> Sent: Saturday, May 21, 2005 22:55
> To: [hidden email]
> Subject: [Elecraft] K2/XV144 Power Overshoot
>
>
> _______________________________________________
> Elecraft mailing list
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> You must be a subscriber to post to the list.
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