[Elecraft] [KX3] Frequency Drift on JT-65

[Lance Collister, W7GJ]

Hi Fred,

I also found that the KX3 was not stable enough for JT65A on 6m, and am still hopeful 
of an eventual solution to this problem, since that is the only reason I invested in 
a KX3. I suspect more people will be interested in KX3 frequency stability as the new 
narrower JT9 mode of WSJTX becomes popular on the low frequency bands. The more 
recent firmware includes a Temperature Compensation program that you can use to 
achieve reasonable JT65A frequency stability on 6m, and suitable stability on HF ; I 
am not sure if it can render the KX3 stable enough for the newer modes such as JT9. 
It will be interesting for low band devotees to determine how the KX3 performs on 
this powerful new mode:

http://www.physics.princeton.edu/pulsar/K1JT/WSJT-X_Quick_Start_Guide.pdf

I found that with the addition of finned heat sinks on the PA and the OSC, the KX3 
runs much cooler in JT65A mode, and quickly reaches its operating temperature within 
the first couple of seconds) and cools down to its receive temperature well before 
the next JT65A receive period begins. Here is what I wound up doing with my KX3:

http://www.bigskyspaces.com/w7gj/KX3HeatSinks.htm

Careful examination of the SpecJT waterfall traces above indicate that there still is 
a small frequency jump of several Herz at the start of every transmission period, 
apparently before the temperature compensation can be applied. This one or two second 
delay appears to be due to a physical separation between the OSC and the temperature 
sensor in the hardware. It would be interesting to have the firmware immediately set 
the temperature value (and invoke the suitable temperature correction value) at a 
user-definable increase from the receiving temperature for a user definable period 
during the start of a transmission sequence.... In my case, I would select a 2 degree 
C temperature jump for the first second. After that, things seem to be relatively 
constant, and the temperature compensation routine in the firmware does a pretty good 
job of keeping the KX3 transmitting on frequency.

I only use JT65A from WSJT on 6m and am not familiar with JT65-HF. However, I think 
the results that I have achieved would work successfully for JT65A on 6m as long as 
the receiving station uses the AFC option to receive my JT65A. I don't know if you 
have such an option in JT65-HF, but I strongly suspect that it would not be required 
for you, since you should be able to achieve viable frequency stability on HF with 
the Temperature Compensation routine in the KX3 firmware.

GL and VY 73, Lance


On 11/19/2012 12:28 AM, k5frd wrote:
>
> I have received numerous messages via JT-65 of frequency drift. I have also 
> observed this problem using another receiver and monitor. Have also confirmed that 
> the problem is causing failed contacts. Power output is 2W into a Hardrock 50 amp. 
> Also confirmed problem using 5W direct to ant from KX3. Problem exists at all times 
> regardless of power and time for warm up. Same problem exists with WSPR. Is there a 
> solution for this serious fault? My KX3 was built and calibrated at the factory.
> Thanks,
> Fred
>
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-- 
Lance Collister, W7GJ
(ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ, E6M)
P.O. Box 73
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