[Elecraft] [KX3] JT65 and JT9 possible TX issues

[Fred Jensen]

On 5/9/2015 2:14 PM, Bob Towers wrote:

> I recently had my first few JT65 QSOs on 20m using my K2/100. I set the
> power level to 5 watts and was astonished to hear the fan at the back of
> the K2 come on in the middle of a TX session. The heatsink coped pretty
> well and no one complained of drift, so JT65 QSOs were entirely
> possible. Had I increased the power to 10 watts, I suspect there may
> have been problems.

For RTTY, I stuck a computer fan to the top of the amp-in-the-lid with a 
little tab of velcro, blowing down.  Heat sink stayed totally cool even 
after calling CQ with 3 sec breaks almost continuously.  I finally sold 
the amp, I began using the K2 as a QRP field rig after I got the K3 so I 
can't send you a photo, but it was pretty easy.  When I wasn't on RTTY, 
I just pulled the fan off.

If you lower the power below the amp's threshold, I believe it shuts 
down and you're using the QRP PA's in the basic K2.  I don't know how 
the thermodynamics work in that situation ... that is, if the amp's heat 
sink functions with the base PA transistors or not.  It may be that 
15-20W [using the amp] would work better than 5W using the basic PA's.
>
> As far as I'm concerned, JT65 is a weak signal mode and in my book even
> 5 watts is probably too much!

Sort of.  JT65 *is* a weak signal mode, and if you're working a QRP 
station with perhaps a compromised antenna, he will likely be weak. 
Ditto for an EME station, however there is nothing inherently "QRP" 
about JT65, and "weak signal" does not automatically imply low power. 
In EME usage, some pretty hefty powers and antennas are employed ... and 
you'll still be weak coming back down. :-)

JT65 will permit QSO's at and below the noise level regardless of what 
the transmit power is ... the trade-off is it requires a lot of patience 
and you don't get to be very creative in what you say.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
- www.cqp.org