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BITX40 with QRPLabs VFO

 

Hi Kent

First check your firmware version, it is displayed at startup. For use with the BITX40 you need version s1.02a or above.?

Set the IF offset parameter to -012,000,000

Later you may refine that to the exact BFO frequency, if you can measure or infer it.

If you use the GPS and set the GPS Mode Baud parameter to 2 009,600 (which i suppose you did already) then the reference frequency is automatically calibrated.?

Otherwise (with no GPS) the Ref Freq parameter also needs to be set to the exact reference crystal frequency. If you set it to 27,004,000 the VFO will be within a couple of hundred Hz and you can improve on that later.

Please let me know if any other questions!

73 Hans G0UPL?
?
 

Thanks for the great info, Hans!? Firmware is s1.02c.? The other piece that I'm sure I saw before, ?but I can't seem to find now. ? What are the pin connections between the BITX40 and the VFO module? I know I'm supposed to connect Clk0 and Ground on the VFO, just need to figure out which is which on the BITX.

Kent
W9WB

On Dec 31, 2016 12:49 AM, "Hans Summers hans.summers@... [BITX20]" <BITX20@...> wrote:
?

Hi Kent

First check your firmware version, it is displayed at startup. For use with the BITX40 you need version s1.02a or above.?

Set the IF offset parameter to -012,000,000

Later you may refine that to the exact BFO frequency, if you can measure or infer it.

If you use the GPS and set the GPS Mode Baud parameter to 2 009,600 (which i suppose you did already) then the reference frequency is automatically calibrated.?

Otherwise (with no GPS) the Ref Freq parameter also needs to be set to the exact reference crystal frequency. If you set it to 27,004,000 the VFO will be within a couple of hundred Hz and you can improve on that later.

Please let me know if any other questions!

73 Hans G0UPL?
?
Jack Purdum
 

Strange...I ordered two BITX40's on Dec. 26 and just got notice that "they were shipped". However, the notice says the package was $12 when my PayPal account was debited the correct amount of $118. Is this normal?

Jack, W8TEE
 

Connections between the VFO and the Bitx are Clock 0, ground, the to the 2 pin connector next to the vfo coil approximately in the middle of the board. You have to remove ?the VFO coil as per instructions. I also put a 40 meter low pass filter in series with the VFO lines and the BitX connection. I'm not sure it made any difference, however it should turn the VFO square wave into a sine wave, and it's said to cut down the noise generated by the VFO.?
 

Hi

> On my QRP-LABS DDS VFO, my correction came out to 27.010.5. So it?
> was a matter of fiddling with it, and I was able to tune it in by listening to?
> a known station frequency like East Cars, and calibrating the vfo so it?
> sounded natural. Finally I got an on air check with my buddy cross town.?
> All good. BTW I have the new corrected software on the way.

If it all works fine and you're happy with it, that's fine. But just FYI...

The 27MHz crystal in the QRP Labs Si5351A Synth kit usually oscillates between 27.003 and 27.005. I have never heard a case of it oscillating as high as 27.0105. To be absolutely correct what you would need to do is adjust the programmed IF frequency to the actual BFO frequency of your BITX40. You probably entered "IF Offset" parameter "-012,000,000" but in reality the actual BFO frequency of your BITX40 will be a kHz or more lower than that. So what you have done by setting such a high "Ref Freq" parameter (27.0105) is cancelled out the error in the IF you entered. But the cancellation will only be perfect at one particular frequency.?

It's not important - because the BITX40 only operates over a narrow frequency range anyway. I'm just saying, to really be technically perfect one should adjust the BFO frequency as well as the 27MHz Ref Freq. But I know that is not necessarily easy if you are doing it by listening to a known station frequency.

73 Hans G0UPL

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