[Elecraft] [KX3] JT65-HF KX3 Freq Drift Measurements

[Gary Hawkins]

The only other working receiver I have at home is an aging (30 years at 
least old) Yaesu FT-690R.  So I switched it on for the first time in at 
least two years and within 30mins I'd convinced myself its receive freq 
stability was such (after a little warm-up time) that I could measure TX 
relative drift of a receive 6m signal down to 1 or 2Hz accuracy.  Thus, 
with the FT-690R connected through my Signalink to the WSJT-X waterfall 
I went about measuring my KX3 freq variation under TX conditions.

KX3 TX power = 3W to dummy load, freq 50.076MHz, FM modulation 
continuous TX until PA temp reach 55C.  Starting PA temp reported at 30C:

  * total min-to-max freq drift averaged over four runs was a staggering
    104Hz, occurring over approx 2 mins;
  * minimum freq observed around 40C.  Initially freq drifts down,
    reaches minimum point and then drifts positive.

So my next thought was could I observed performance on a lower band.  
Well, the only band that offered any possibility was operating on 30m 
and looking for the 5th harmonic on the FT-690R. To my slight surprise 
with the KX3 transmitting at 10.1MHz, I found a weak 5th harmonic that I 
could observe on the FT-690R at 50.5MHz.  Keying the KX3 resulting in 
the 5th harmonic appearing and disappearing.  KX3 TX power = 3W to dummy 
load, KX3 freq 10.1MHz, FM modulation continuous TX until PA temp reach 
40C (seemed to stabilize at this max temp).  Starting PA temp reported 
at 27C.  FT-690R monitoring 50.5MHz:

  * total min-to-max freq drift averaged over four runs 40.5Hz, _which
    considering I'm looking at the fifth harmonic is really 8.1Hz_
    occurring over approx 4-5 mins;
  * minimum freq observed around 32C.  Initially freq drifts down,
    reaches minimum point and then drifts positive.

For those that have done similar tests on an uncompensated KX3, do these 
results seem reasonable?  If they are reasonable is it safe to say that 
successful 6m JT65/JT9 operation even after extended temperature 
compensation is unlikely?

73's Gary K6YOA

_Please note these results are not a KX3 that has not gone through the 
Extended Temp Compensation. _ That being said, while I think extended 
temp compensation would likely prove sufficient for JT65-HF or JT9 for 
30m and surrounding bands, I will be very surprised when I do the temp 
compensation over the weekend, whether it can sufficiently correct the 
xxxHz drift I'm seeing on the 6m band.

On 5/13/2015 6:01 PM, Tony Estep wrote:
> On Wed, May 13, 2015 at 7:47 PM, Gary Hawkins <gary at hawkins-zhu.com 
> <mailto:gary at hawkins-zhu.com>> wrote:
>
>     ...Does anyone know how I can estimate KX3 freq drift....
>
> ===============
> Gary, if you have another receiver it's easy. Just set up the other rx 
> for JT65HF, transmit via the KX3, and look at the received trace. You 
> can see drift down to a couple of Hz.
>
> I found the drift not to be too dependent on power level. Even at very 
> low levels of output power, my KX3 drifted about the same (about 18 
> Hz) before the temperature compensation. This is too much for JT65HF 
> communication.
>
> 73,
> Tony KT0NY