Re: Drift


Hans Summers
 

Hi Vernon

The LPF would not cause drift. Drift is related only to the 27MHz Si5351A reference oscillator. 20m is the first transmission after your calibration pause. Things I would try myself: 

1) Take a look at http://www.qrp-labs.com/synth/freqstab.html just to be sure you did everything it mentions there. I don't think you put a heatsink on the 27MHz crystal. That can be useful sometimes. An old nut glued on is good enough. Here, I find any suitable small piece of metal around the workbench and glue it on with epoxy. 

2) You mentioned that your frame contains only 30 seconds of non-transmit time. Of that, you have your calibration set to run for 10 seconds. Calibration is done at a much lower frequency, where the microcontroller is able to measure it. That means that the synth will only operate at the Park Mode 2 frequency of 150MHz for 20 seconds. Probably it is not enough to heat the Si5351A up enough. I suggest increasing your "Frame" parameter, add 2 minutes to it. Then The Si5351A will have 2 extra minutes at 150MHz "Park" to stabilise itself. 

3) Try Park at 150MHz, and try it at a much lower frequency e.g. try it at 14MHz (same as transmit frequency). What is the drift, in each case? If you find that drift is positive in one case, and negative in the other, then this means that in your particular situation, 150MHz is too high. It is OVER-compensating, heating up the Si5351A too much, so that when you come to the 20m transmission, it is cooling down and drifting. The solution is to try lower frequencies than 150MHz. 

I recommend trying these things one by one, not all at the same time. One by one means you will be able to find out which one (hopefully) reduces the 2Hz drift to 0Hz. 

73 Hans G0UPL

On Wed, Nov 15, 2017 at 12:36 AM, Vernon Matheson <vmath@...> wrote:

Hi all,


Have been working on getting zero drift and frequency stability on one of my U3S units.


So far...


- Added a small heat sink on top of the 27 mhz xtal

- Packed the area around the xtal between the SI card and the bottom of the LPF board with cotton wool to keep the air currents on the 27mhz xtal. Unit is in QRP labs case as well.

- Set the park mode to 2 with a frequency of 150,000,000

- orientated the LPF board and TX schedule from highest to lowest frequency

- calibration set to 10 020

- added to the end of the frame a slow hell tx so to transmit and leave 30 seconds for calibration.

The results are that every band except 20 meters shows 0 drift.  It can run all night and it doesn't change.

Can anyone give some in-site on this..could there be something off with the LPF for 20M..

Thanks in advance..


Vernon - VE1VDM / VA1VM




2017-11-14 21:24   VA1VM   7.040168   -17   0   FN85ij   0.2   VE3LC   FN25   916   275 
 2017-11-14 21:24   VA1VM   7.040158   -21   0   FN85ij   0.2   K2DUV   FM17tq   1383   236 
 2017-11-14 21:24   VA1VM   7.040150   -16   0   FN85ij   0.2   KK1D   FN31   899   244 
 2017-11-14 21:24   VA1VM   7.040167   -19   0   FN85ij   0.2   N0UR   EN33   2358   275 
 2017-11-14 21:24   VA1VM   7.040150   -14   0   FN85ij   0.2   WA2ZKD   FN13ed   1167   263 
 2017-11-14 21:24   VA1VM   7.040162   -23   0   FN85ij   0.2   N4TVC   FM18is   1367   242 
 2017-11-14 21:24   VA1VM   7.040150   -20   0   FN85ij   0.2   K9AN   EN50wc   2102   263 
 2017-11-14 21:24   VA1VM   7.040151   -13   0   FN85ij   0.2   N2HQII   FN13rp   1067   264 
 2017-11-14 21:24   VA1VM   7.040155   -23   0   FN85ij   0.2   KB9AMG   EN52tx   2010   271 
 2017-11-14 21:24   VA1VM   7.040149   -14   0   FN85ij   0.2   WB3DZC   FM07ux   1490   242 
 2017-11-14 21:24   VA1VM   7.040140   -23   0   FN85ij   0.2   VE3GTC   FN25ig   937   273 
 2017-11-14 21:24   VA1VM   7.040138   -18   0   FN85ij   0.2   K3EA   FN20of   1098   243 
 2017-11-14 21:24   VA1VM   7.040150   -21   0   FN85ij   0.2   K2GQT   FN20wb   1064   240 
 2017-11-14 21:24   VA1VM   7.040151   -23   0   FN85ij   0.2   K2RWF   FN20   1100   244 
 2017-11-14 21:24   VA1VM   7.040162   -27   0   FN85ij   0.2   VE3GHM   FN25ig   937   273 
 2017-11-14 21:24   VA1VM   7.040150   -17   0   FN85ij   0.2   K8HSQ   EN90fu   1561   258 
 2017-11-14 21:24   VA1VM   7.040100   -4   0   FN85ij   0.2   N8VIM   FN42fq   724   248 
 2017-11-14 21:22   VA1VM   10.140151   -2   0   FN85ij   0.2   SWLNXZ   FN13co   1165   265 
 2017-11-14 21:22   VA1VM   10.140154   -25   0   FN85ij   0.2   VE3RPH   FN03hq   1287   267 
 2017-11-14 21:22   VA1VM   10.140148   -22   0   FN85ij   0.2   WQ5O   EN53uk   1989   273 
 2017-11-14 21:22   VA1VM   10.140150   -27   0   FN85ij   0.2   WE4X   EM65ut   2204   249 
 2017-11-14 21:22   VA1VM   10.140161   -28   0   FN85ij   0.2   WD8CIV   FN13if   1138   263 
 2017-11-14 21:22   VA1VM   10.140148   -10   0   FN85ij   0.2   K9AN   EN50wc   2102   263 
 2017-11-14 21:22   VA1VM   10.140155   -22   0   FN85ij   0.2   W3HH   EL89vb   2458   229 
 2017-11-14 21:22   VA1VM   10.140149   -14   0   FN85ij   0.2   W3CSW   FM19kd   1331   243 
 2017-11-14 21:22   VA1VM   10.140149   -23   0   FN85ij   0.2   W4ENN   EM64ru   2286   247 
 2017-11-14 21:20   VA1VM   14.097114   -29   -2   FN85ij   0.2   KD6RF   EM22   3071   253 
 2017-11-14 21:20   VA1VM   14.097148   -18   -2   FN85ij   0.2   KB8SPI   EN82hm   1634   266 
 2017-11-14 21:20   VA1VM   14.097149   -18   -2   FN85ij   0.2   K9AN   EN50wc   2102   263 
 2017-11-14 21:20   VA1VM   14.097154   -22   -2   FN85ij   0.2   KU4QI   EM87bx   1890   251 
 2017-11-14 21:20   VA1VM   14.097146   -16   -1   FN85ij   0.2   KB9AMG   EN52tx   2010   271 
 2017-11-14 21:20   VA1VM   14.097153   -25   -2   FN85ij   0.2   KA4PKB   EN41kf   2287   268 
 2017-11-14 21:14   VA1VM   7.040139   -12   0   FN85ij   0.2   K3EA   FN20of   1098   243 
 2017-11-14 21:14   VA1VM   7.040101   +2   0   FN85ij   0.2   N8VIM   FN42fq   724   248 
 2017-11-14 21:14   VA1VM   7.040150   -20   0   FN85ij   0.2   K8HSQ   EN90fu   1561   258 
 2017-11-14 21:14   VA1VM   7.040170   -26   0   FN85ij   0.2   F5OIH   JN06ci   4780   65 
 2017-11-14 21:14   VA1VM   7.040150   -15   0   FN85ij   0.2   WB3DZC   FM07ux   1490   242 
 2017-11-14 21:14   VA1VM   7.040159   -25   0   FN85ij   0.2   K2DUV   FM17tq   1383   236 
 2017-11-14 21:14   VA1VM   7.040168   -14   0   FN85ij   0.2   VE3LC   FN25   916   275 


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