[Elecraft] [wsjtgroup] Frequency Stability Needed for FT8, JT65, MSK144?

[Lance Collister, W7GJ]

Hi Jim,

Since MSK144 has a bandwidth about 10 times the size of JT65A, I expect that any KX3 
calibrated with the temperature compensation routine 
(http://www.elecraft.com/manual/KX3%20Custom%20VFO%20TC%20rev%20A9.pdf) should work 
OK. As you know, KX3 units with number above about 10,000 have the new main RF board, 
and should be quite stable even for narrower weak signal modes as long as the 
temperature compensation routine is done correctly.

My early KX3 is number 800 something, so it has the original RF board, and there was 
a big problem with resistors heating up during transmit which caused the nearby 
oscillator to change frequency suddenly.  Five years ago, I had hoped that adding big 
heat sinks and coupling the oscillator to those would make the KX3 stable enough for 
JT65A on 6m for EME.  Although it helped, the ultimate solution was to remove the two 
problem resistors from the RF board, and replace them with a single tiny flange mount 
20w resistor (AVX100) mounted directly to the case/heat sink, and coupling the 
temperature sensing IC more closely to the oscillator.  The stability now rivals my 
K3 with the optional high stability oscillator.

Full details of the modifications are shown on my web page here:

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

My current objective in improving the stability was to be able to use the KX3 in FT8 
mode for SOTA activations.  I now feel very confident that the KX3 is stable enough 
for that, or for other weak signal modes such as JT65A even up on 6m.

GL and VY 73, Lance

On 2/27/2018 05:33, Jim Brown k9yc at audiosystemsgroup.com [wsjtgroup] wrote:
> I'm part of a team planning for a summer assault on CM79 (6M operation).
> It's a challenging hike -- 3 miles +1,000 ft elevation, and all the guys
> going up the trail are in their mid-70s. Previous trips have been CW
> only with a KX3 and the 100W amp. Our objective is to fill grids for
> FFMA and VUCC chasers. Our most satisfying QSO last year was with ND0B,
> who I think needs only one more for FFMA. One of the guys going up the
> trail will be K6EU, a very experienced WSJT op. I'll be pilot. There are
> a lot of guys trying to work us within MS and tropo range that we
> couldn't hear on CW.
>
> W7GJ has identified frequency stability issues with that rig, and
> implemented fixes. Elecraft has also redesigned the main board to
> correct the issues that Lance found, eliminating the need for much of
> what Lance developed, and I'm corresponding with Wayne Burdick, Elecraft
> owner and chief engineer about it.
>
> My question is simple -- what target do we need to hit? How much short
> term drift can each of these modes tolerate before decoding is degraded?
> I'm guessing wider for MSK144.
>
> Thanks and 73, Jim K9YC
>
>
>
> ------------------------------------
> Posted by: Jim Brown <k9yc at audiosystemsgroup.com>
> ------------------------------------
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-- 
Lance Collister, W7GJ(ex WA3GPL, WA1JXN, WA1JXN/C6A, ZF2OC/ZF8, E51SIX, 3D2LR, 5W0GJ, E6M, TX5K, KH8/W7GJ, V6M, T8GJ, VK9CGJ, VK9XGJ)
P.O. Box 73
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USA
TEL: (406) 626-5728
QTH: DN27ub
URL: http://www.bigskyspaces.com/w7gj
Skype: lanceW7GJ
2m DXCC #11/6m DXCC #815

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