Posted by
w2bvh on
Dec 06, 2010; 2:34am
URL: http://elecraft.85.s1.nabble.com/K2-XV-144-with-sequencer-and-big-amp-tp5806317p5806509.html
I faced this issue just recently with a K2 and my homebrew 2M
transverter when putting a used 550 W dual 4cx250 power amp into service.
In the long run its best to make the mod to the K2 Don W3FPR outlines on
his web page and I intend to do so some time soon. But as a quick hack
to get on the air I built up a little circuit consisting of a one-shot
and 2 relays that goes in the transverter,
It works as follows: the relay is interposed between the output of the
power attenuator at the I.F. input of the transverter and the first
stage in the transverter's transmit string (the first stage in this case
is the transmit mixer).
When the K2's keyline is asserted (low) it triggers the one-shot which
activates one relay for 35 ms, The relay is driven by a general purpose
npn transistor. While the the relay is driven, it puts a 51 ohm resistor
across the output of the the power attenuator and opens the path
between the power attenuator and the mixer. This prevents the K2's rf
from reaching the transverters transmit mixer for the duration of the
one-shot. After 35 ms have gone by (enough time for the power amps tr
relay to engage) the one-shot times out, reconnecting the power
attenuator to the transmit mixer. The keyline signal also goes to a
second relay via a general purpose npn transistor. That relay drives the
keyline of the power amplifier.
I used an HCF4047 one-shot which happily runs off the 13.5V transverter
power. The relays are a small inexpensive Omron units.
You could probably do something similar to this scheme but *external* to
your XV144 and get similar results.
The upside is that the power amp is not hot switched. The downside is
that the around 20 ms of the first element in the first morse character
is clipped off. Additionally that same morse element does not have a
controlled rise time since it *is* hot switched (in my case at
approximately -4 dBm). So you get a slightly shortened first dit or dah
with a single key click for that element. For me it was a worthwhile
temporary compromise.
It is disappointing that the K2 doesn't have a settable delay for the
onset of rf. A small oversight in an otherwise excellent rig (I've had
mine for over 10 years).
73,
Lenny W2BVH
On 12/5/2010 7:00 PM, Bob DeVarney W1ICW wrote:
> Second question.
> I am using my K2 and XV-144 as my EME rig. I take the output of the
> transverter key jack and feed it to my sequencer, which then sends the
> appropriately delayed signals to my amp ( 750 watts ) and my T/R relays
> and preamp at the tower.
>
> My question is this:
>
> Can I slow down the transition from receive to transmit internal to the
> K2? Is there a menu option to do so? I could of course use the ptt
> signal from my computer to key my sequencer, and then have my sequencer
> key the K2, but what if I use the "tune" button on my front panel? That
> appears to be instantaneous.
> The last thing I want to do is wipe out a very expensive preamp or hot
> switch my relays with a 1 kW amp ( in the works )
>
>
> Thanks in advance,
>
> Bob W1ICW
>
> P.S. I have rediscovered my K2 this year, as a high performance VHF rig
> ! K2s aren't just for QRP HF any more, I've made over 170 EME QSOs with
> my K2, XV-144, 600 watts, and a small ( by EME standards ) array of 16
> dBd gain on 2 meters. Bravo to the Elecraft team for coming up with such
> a versatile product !
>
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