开云体育

ctrl + shift + ? for shortcuts
© 2025 开云体育
  1. BITX20
  2. Topics

DDS VFO

[email protected]
 

I set my bitx 40 up with DDS VFO. The DDS VFO is spot on frequency. I set the IF off set to -12MHZ. The radio seams to be off frequency. Looks like about 1.5 kc. And the transmite is different then receive frequency. Did I set the IF out set wrong? Should I try to adjust the IF some how? I see parts missing for any IF adjustments.

Thanks

Bill N3JHS
 

开云体育

Bill,

I had to set the the IF for the BFO frequency which on mine was 11.998.6, that put it right on frequency. It sounds like your BFO is 1.4KHz less than the 12MHz IF like mine.

Joel Caulkins
KB6QVI

On Nov 26, 2016, at 5:08 PM, bill@... [BITX20] <BITX20@...> wrote:

?

I set my bitx 40 up with DDS VFO. The DDS VFO is spot on frequency. I set the IF off set to -12MHZ. The radio seams to be off frequency. Looks like about 1.5 kc. And the transmite is different then receive frequency. Did I set the IF out set wrong? Should I try to adjust the IF some how? I see parts missing for any IF adjustments.

Thanks

Bill N3JHS
Bill Kittilson
 

开云体育

Ok thanks. I'll try to measure my BFO on the scope and set that for my IF. ?

The tx and rx must follow each other right? They can't be different. ?

On Nov 26, 2016, at 8:23 PM, Joel Caulkins caulktel@... [BITX20] <BITX20@...> wrote:

?

Bill,

I had to set the the IF for the BFO frequency which on mine was 11.998.6, that put it right on frequency. It sounds like your BFO is 1.4KHz less than the 12MHz IF like mine.

Joel Caulkins
KB6QVI

On Nov 26, 2016, at 5:08 PM, bill@... [BITX20] <BITX20@...> wrote:

?

I set my bitx 40 up with DDS VFO. The DDS VFO is spot on frequency. I set the IF off set to -12MHZ. The radio seams to be off frequency. Looks like about 1.5 kc. And the transmite is different then receive frequency. Did I set the IF out set wrong? Should I try to adjust the IF some how? I see parts missing for any IF adjustments.

Thanks

Bill N3JHS
 

bill,
i should permanently document this somewhere. the LSB pass band of a ladder filter is invariably below the marked frequency. so, if you set the dds for exactly 12 mhz, it won't be precise.
the most accurate way is to measure the bfo frequency on your board. the rule of thumv is to set the IF frequency to 11.99850 Mhz
- f


On 27-Nov-2016 6:38 am, "bill@... [BITX20]" <BITX20@...> wrote:
?

I set my bitx 40 up with DDS VFO. The DDS VFO is spot on frequency. I set the IF off set to -12MHZ. The radio seams to be off frequency. Looks like about 1.5 kc. And the transmite is different then receive frequency. Did I set the IF out set wrong? Should I try to adjust the IF some how? I see parts missing for any IF adjustments.

Thanks

Bill N3JHS
Bill Kittilson
 

开云体育

Thanks!?
That made the rx spot on. ?I'll check tx tomorrow. ?

I also noticed that my DDS has a rit set. I turned that off. ?That should help.?

Thanks for a making the board available. This has been a fun project.?

On Nov 26, 2016, at 9:00 PM, Ashhar Farhan farhanbox@... [BITX20] <BITX20@...> wrote:

?

bill,
i should permanently document this somewhere. the LSB pass band of a ladder filter is invariably below the marked frequency. so, if you set the dds for exactly 12 mhz, it won't be precise.
the most accurate way is to measure the bfo frequency on your board. the rule of thumv is to set the IF frequency to 11.99850 Mhz
- f


On 27-Nov-2016 6:38 am, "bill@... [BITX20]" <BITX20@...> wrote:
?

I set my bitx 40 up with DDS VFO. The DDS VFO is spot on frequency. I set the IF off set to -12MHZ. The radio seams to be off frequency. Looks like about 1.5 kc. And the transmite is different then receive frequency. Did I set the IF out set wrong? Should I try to adjust the IF some how? I see parts missing for any IF adjustments.

Thanks

Bill N3JHS
 

Okay I have the same issue with my Bitx40 and Qrp-labs Vfo combination. Currently I am running the vfo at 2khz below the desired frequency. Additionally when I transmit my ssb voice signal is clear about 1.6 khz below that. So I'm looking for some sort of adjustment for the BFO, and I see there is a spot for a variable cap that does not exist on the board. While I may have a problem with the VFO, (new software version chip on order) how do I correct the BFO issue? Do I need to add a trim cap to the bfo circuit??
 

. I found a calibration adjustment for the vfo, Instead of 27 mhz reference frequency, I adjusted it to 27010.050 which seems to put it almost dead on. I haven't really checked the transmit yet, but in a receiver it seems like it might be okay. I'll check with my friend in town later today.?

1 - 7 of 7