[Elecraft] Re: KX1 BFO Calibration

[Randy Foltz]

I think I've got this figured out.

I checked all the components Wayne and Gary suggested.  They are all 
correct.

CHU transmits USB with a re-introduced carrier not AM.  You can hear 
(and see on Spectrogram) the carrier.

This is what I did.

1) Select USB and tune CHU until the carrier is at zero on the 
Spectrogram display.  Actually hard to do as the signal gets weak and 
there is also a 60 Hz signal too, but you can get it close.

2) Note the frequency.

3) Switch to LSB and tune CHU until the carrier is at zero on 
Spectrogram again.

4) Note this frequency.

5) Subtract the two and follow the KX1 instructions for determining the 
sign.  For mine the correction was -0.30.

6) Enter this into the KX1 as the BFO parameter.

7) There will still be a difference between the USB and LSB fqs that 
show the carrier at zero.  For my KX1 this was 1.57 kHz.  I checked my 
K2 and it has a similar difference between the USB and LSB fqs that show 
the carrier at zero.  For the K2 it was 1.83 kHz.  I suppose this fq 
difference is because CHU is transmitting in USB rather than AM.

8) To set the DDS parameter select USB and dial in 7335.00 then follow 
the KX1 manual by changing the parameter until the 1000 Hz ticks appear 
at the 1000 Hz marks in Spectrogram.  For my KX1 this value was 37.

After this all seems great.

73,
Randy, K7TQ

Gary Surrency wrote:
> He might have the wrong value caps or RF choke in the BFO circuit too. L10
> must be 33uH. Check that C13 (56pF, often marked 560J) and C14 (330pf,
> marked 331J) are not swapped.
> 
> --
> 73, Gary AB7MY
> =========
> gary@elecraft.com
> Elecraft Technical Support  
>  
> 
> 
> 
> -----Original Message-----
> From: Wayne Burdick [mailto:n6kr@elecraft.com] 
> Sent: Tuesday, December 30, 2003 12:12 AM
> To: Randy Foltz
> Cc: Elecraft; support@elecraft.com
> Subject: Re: KX1 BFO Calibration
> 
> 
> Hi Randy,
> 
> This should never happen. Typical BFO corrections are on the order of -0.20.
> We match the crystals very closely.
> 
> It sounds as if your BFO is way off frequency frequency. Do you have a
> frequency counter? If so, you can touch it to pin 7 of the product detector
> (NE602, U4) to see what the actual BFO frequency is. Check all components in
> this area; you could have the wrong value of C13, C14, or L10. 
> 
> Also check the labeling on your BFO crystals. We have to make sure you
> didn't get the wrong type. They should all have the same markings.
> 
> Wayne
> N6KR
> 
> Randy Foltz wrote:
> 
>>After making several 40 m QSOs, I decided to do the BFO calibration. 
>>After a 15 minute warm up period I tuned CHU at 7.335 MHz.  The BFO 
>>parameter was set to .00 and the DDS one to 00.  Using Spectrogram to 
>>display the 1000 Hz tick marks I recorded the fq as 7334.74 in USB and 
>>7337.35 in LSB.  This difference is 2.61 and when divided by 2 gives a 
>>BFO correction of 1.30. Since the USB was lower the correction should 
>>be -1.30.  Woops, the maximum negative value is 0.99.
>>
>>I went ahead and set the -0.99 and recorded the fqs again.  This time 
>>they were 7335.74 for USB and 7336.36 for LSB.  Closer together, but 
>>still not the same.
>>
>>I took out the ATU, repeated the test, and the results were the 
>>same....
> 
>