Topics

calibration of U3S + GPS #u3s #si5351a #qlg1

f5ihn
 

Dear all,

currently testing the U3S + si5351a and its GPS on 40 m band.
The actual TX frequency is abt 200 Hz too high.
The assembling manual page 19 says that no calibration is required when having the GPS, with regards to the 27 MHz "Ref. Frq" parameter.
It is said also that the internal freq would be 26.998 rather than 27.004 when having the GPS. Looking in the parameters, 27.004 is shown instead of 26.998.
I don't know if the parameter is updated according to the effective value (when having the GPS present).

Of course the 1 pps signal is present at the U3S input connector. Does it mean in turn that U3S doesn't see the 1 pps signal ?

I plan to slightly change "Ref. Frq" and look for any change in the output freq.

In addition, I'm not sure to understand correctly how to manage the Cal (Step time) and Pak (Mode freq) parameters. Any reference settings that work with your units ?

Any other idea/comment is welcomed !

73's de F5IHN David


Alan G4ZFQ
 

The actual TX frequency is abt 200 Hz too high.
The assembling manual page 19 says that no calibration is required when having the GPS, with regards to the 27 MHz "Ref. Frq" parameter.
David,

Page 15 tells you about calibration.
If you have PPS then GPS must be enabled. Then set calibration as suggested on page 15, make step (default 1) larger to calibrate quickly, then smaller for final accuracy .

It is said also that the internal freq would be 26.998 rather than 27.004 when having the GPS. Looking in the parameters, 27.004 is shown instead of 26.998.
~27.004 is normal for the standard crystal.

I plan to slightly change "Ref. Frq" and look for any change in the output freq.
Calibration should do this.

73 Alan G4ZFQ

Chris Wilson
 

Hello Alan,

Tuesday, September 17, 2019

OK, call me dumb, I have broad shoulders and a sense of humour :) I
have never really understood this section of the manual:

"Once you have measured the actual output frequency, you can
calculate the required correction to the 27MHz reference frequency
and enter it in the “Ref. Frq.” configuration setting. For example,
suppose you set the output frequency to 13.500000 MHz but you
actually measure 13.500075. Your output frequency is 75 Hz too high.
Since your output frequency setting is 2 times less than the 27MHz
reference oscillator frequency, this means that the actual reference
oscillator value is 150Hz too high. So enter 27,000,150 in the “Ref.
Frq.” setting."

In particular : " this means that the actual reference
oscillator value is 150Hz too high. So enter 27,000,150 in the “Ref.
Frq.” setting."

I have always thought this should read 26,000,850 in the Reference
Frequency setting if it was too high....


Now, make me look an idiot and teach me where I am going wrong
please.

I work solely LF with my GPS locked U3S so just set the TX frequency 2 Hz low
and compensate the tiny error that way. probably because I don't
understand that section of the manual.... ;)


Best regards,
Chris 2E0ILY mailto:chris@...


The actual TX frequency is abt 200 Hz too high.
The assembling manual page 19 says that no calibration is required when
having the GPS, with regards to the 27 MHz "Ref. Frq" parameter.
AG> David,

AG> Page 15 tells you about calibration.
AG> If you have PPS then GPS must be enabled. Then set calibration as
AG> suggested on page 15, make step (default 1) larger to calibrate quickly,
AG> then smaller for final accuracy .

It is said also that the internal freq would be 26.998 rather than
27.004 when having the GPS. Looking in the parameters, 27.004 is shown
instead of 26.998.
AG> ~27.004 is normal for the standard crystal.

I plan to slightly change "Ref. Frq" and look for any change in the
output freq.
AG> Calibration should do this.

AG> 73 Alan G4ZFQ

AG>



--
Best regards, Chris Wilson (2E0ILY)

f5ihn
 

Hello Alan,

thanks for the quick reply.
Indeed the GPS must be enabled, and it is so. Current time is display and I can get all the GPS data on the stand-by screen display.

I believe also that the GPS would calibrate.
I remember about one thing: as explained page 23 od the Operation manual, a heart beat symbol should be displayed. It is not. That makes me wondering if the U3S really see the GPS ...
I will trace the 1 pps signal til the MCU, this evening.

I will double check "Cal time" and "Cal step" so the calibration can complete, I'm not sure about the value I entered. Anyway I assume I should see the heart symbol.

73
F5IHN David

Alan G4ZFQ
 

I assume I should see the heart symbol.
David,

Yes, provided that the GPS is locked.
If the QLG1 flashes then the heartbeat should be seen.

73 Alan G4ZFQ

Alan G4ZFQ
 

Chris

For example, > suppose you set the output frequency to 13.500000 MHz but you>
actually measure 13.500075. Your output frequency is 75 Hz too high.

So the U3 is thinking the crystal is lower than it actually is. It is informed by what the stored Reference Frequency tells it.
I guess we all get confused by this, I have to stop and think.
I hope that is correct:-)

73 Alan G4ZFQ

Chris Wilson
 

Hello Alan,

Tuesday, September 17, 2019

Thank you Alan, I believe I see it now, and I am sure you are
correct, but I would respectfully suggest some additional or changed
wording in the manual might make this a little clearer. If *YOU* have
to doubt in some little way if you have it correct us "mere U3S
mortals" may justifiably be left a bit perplexed <LOL>. I may enter
the menus tonight and fix my rather horrible kludge! Thanks again.


Best regards,
Chris 2E0ILY mailto:chris@...


AG> Chris

For example, > suppose you set the output frequency to 13.500000 MHz but you>
AG> actually measure 13.500075. Your output frequency is 75 Hz too high.

AG> So the U3 is thinking the crystal is lower than it actually is. It is
AG> informed by what the stored Reference Frequency tells it.
AG> I guess we all get confused by this, I have to stop and think.
AG> I hope that is correct:-)

AG> 73 Alan G4ZFQ

AG>



--
Best regards, Chris Wilson (2E0ILY)

Alan G4ZFQ
 

I would respectfully suggest some additional or changed
wording in the manual might make this a little clearer.
Chris

Yes, the part you quote "In particular : " this means that the actual reference
oscillator value is 150Hz too high. So enter 27,000,150 in the “Ref.
Frq.” setting."

"the actual reference oscillator value" is somewhat confusing, although the end result is correct.
Perhaps it should say "the actual reference oscillator value is too low"?
Hummm the more I look I begin to think it could be explained better, what if the Ref Frq setting was already 27.004,000 then the new Ref would be..?

Output frequency/Frequency Set*Ref Frq = New Ref Frq

13.500075/13.5000000*27.004000 = 27.004152 in this case 152Hz higher than before.

Maybe when I first tried this I got confused and that's why I work it out once more rather than read the instructions and get confused? My maths is just about good enough for me to calculate these frequencies in proportion:-)

73 Alan G4ZFQ

f5ihn
 

Hi,

problem solved !

I was confused by the presence of 1 pps of the yellow led, which in turn is the TX data being sent.
The green led of the real 1 pps signal is off, I checked and the RF module doesn't send any signal.
No short-ciircuit, nor any trouble with the 74ACT08 that I removed for testing.

I replaced the board by another one I purchased earlier for the QCX, and all is fine now.

I'll check with Hans if there's a chance to get an RF module for replacement.

73
F5IHN David