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A note on calibrating the BFO frequency in V6 uBITX radios (V5 too) #v5 #v6

Jim Sheldon
 

Since receiving my V6 uBITX a couple weeks ago and having to fix some errors in the original program code, when I compiled and uploaded the program to the Raduino's NANO, it reset both the frequency and BFO calibration frequencies to the factory default code.

After quite a bit of playing with it, I finally figured out just how it worked and got it square in my head where on the filter passband it should be set to have the correct sidebands when selecting CW/USB/LSB.

The uBITX is an "upconversion" radio where the incoming signal is first converted to the 45 MHz first IF frequency and then mixed with the VFO (clock) signals out of the Si5351 chip on the Raduino to select whether the radio is in SSB or CW mode and which sideband you want to listen to (in either mode).  Since the radio is an UP and then back Down conversion, the sidebands wind up being inverted relative to the filter, so the initial BFO setting MUST be set fairly down the LOWER frequency side of the filter (this actually generates and receives USB before being massaged by the USB/LSB selection routines.

The V6 has a nominal Crystal Filter (IF) frequency of 11.059 MHz.  Because of the capacitors and other circuit loading of the crystals in the circuit tend to move the actual frequency lower, the BFO winds up needing to be around 11.055 MHz to allow enough received signal through the 3.0 or so KHz wide filter.

In my actual experience with both a V5 and a V6 uBITX I've found that a good starting point for calibrating the BFO properly is 11.055.0 MHz as indicated on screen in the BFO calibration routine.  That won't be a perfect setting as each uBITX filter will be slightly different, but should produce usable audio to work with for final tweaking of the frequency.  When you get it set to your satisfaction, BE SURE TO WRITE THIS FREQUENCY DOWN before exiting the calibration routine because as the code is currently written, every time you enter the BFO set menu, it resets the BFO frequency to the factory default which is pretty far off what it really needs to be (in every uBITX I've built and I've built over 10 of them from the V3's to now the V6).

I decided to post this so maybe some of the newer people might have an easier time calibrating their BFO's if they wind up having to re-load the software as each reload sets the frequencies back to the factory defaults which can be pretty far off depending on the actual tolerances of the components in the uBITX filter as built - caused by variations in the individual crystals, capacitors, coils etc., used in that filter.  Each radio WILL be enough different that one frequency will not fit all.

Hope this helps a bit.  Took me a while to get it square in MY mind and I've been doing this stuff since 1963 - LOL.

Jim Sheldon, W0EB
TSW Project Coordinator

 

Jim,
Your observation is spot on, I finally settled on 11.056.0 for my BFO setting, I'm getting great audio reports with this setting also, so this should be a good starting point for anybody.

Joel
N6ALT

Neil k8it
 

Thank you for the V6 BFO 11055 setting. Do you have a suggested setting for set frequency value? Also any suggestion on how to set the 10MHz master clock?
Thanks 73 Neil k8it


On Jan 5, 2020, at 12:13 PM, Joel Caulkins/N6ALT <caulktel@...> wrote:

Jim,
Your observation is spot on, I finally settled on 11.056.0 for my BFO setting, I'm getting great audio reports with this setting also, so this should be a good starting point for anybody.

Joel
N6ALT

Mark WO7T
 

I just wanted to add that the default BFO setting that came with my freshly new assembled V6  #167 was 11.049.8, and upon first firing up, 
I had such awful broadcast interference (1060 AM)  on 7.016mhz and across most of 40M that I deemed this radio was never gonna work
out at my QTH. 

Changed BFO setting to 11.056, and BCI diminished into the background, and SSB audio ALL sounded better.  

73

Mark 


Mick
 

Thanks for the tipJim. I’m picking up my V6 tomorrow and will start setting it up as soon as I get home.

73
Mick VA3EPM

On Jan 5, 2020, at 12:05 PM, Jim Sheldon <w0eb@...> wrote:

Since receiving my V6 uBITX a couple weeks ago and having to fix some errors in the original program code, when I compiled and uploaded the program to the Raduino's NANO, it reset both the frequency and BFO calibration frequencies to the factory default code.

After quite a bit of playing with it, I finally figured out just how it worked and got it square in my head where on the filter passband it should be set to have the correct sidebands when selecting CW/USB/LSB.

The uBITX is an "upconversion" radio where the incoming signal is first converted to the 45 MHz first IF frequency and then mixed with the VFO (clock) signals out of the Si5351 chip on the Raduino to select whether the radio is in SSB or CW mode and which sideband you want to listen to (in either mode).  Since the radio is an UP and then back Down conversion, the sidebands wind up being inverted relative to the filter, so the initial BFO setting MUST be set fairly down the LOWER frequency side of the filter (this actually generates and receives USB before being massaged by the USB/LSB selection routines.

The V6 has a nominal Crystal Filter (IF) frequency of 11.059 MHz.  Because of the capacitors and other circuit loading of the crystals in the circuit tend to move the actual frequency lower, the BFO winds up needing to be around 11.055 MHz to allow enough received signal through the 3.0 or so KHz wide filter.

In my actual experience with both a V5 and a V6 uBITX I've found that a good starting point for calibrating the BFO properly is 11.055.0 MHz as indicated on screen in the BFO calibration routine.  That won't be a perfect setting as each uBITX filter will be slightly different, but should produce usable audio to work with for final tweaking of the frequency.  When you get it set to your satisfaction, BE SURE TO WRITE THIS FREQUENCY DOWN before exiting the calibration routine because as the code is currently written, every time you enter the BFO set menu, it resets the BFO frequency to the factory default which is pretty far off what it really needs to be (in every uBITX I've built and I've built over 10 of them from the V3's to now the V6).

I decided to post this so maybe some of the newer people might have an easier time calibrating their BFO's if they wind up having to re-load the software as each reload sets the frequencies back to the factory defaults which can be pretty far off depending on the actual tolerances of the components in the uBITX filter as built - caused by variations in the individual crystals, capacitors, coils etc., used in that filter.  Each radio WILL be enough different that one frequency will not fit all.

Hope this helps a bit.  Took me a while to get it square in MY mind and I've been doing this stuff since 1963 - LOL.

Jim Sheldon, W0EB
TSW Project Coordinator

Jerry Gaffke
 

Here's an old post that tries to explain why USB vs LSB gets flipped when going through a mixer.
And a bunch of other nitty-gritty details of how a uBitx works.
    https://groups.io/g/BITX20/message/44515
This was written before the switch from a 12mhz IF (v3 and v4) to an 11.059mhz IF (v5 and v6).
Otherwise, everything said applies to all versions of the uBitx.

>  The V6 has a nominal Crystal Filter (IF) frequency of 11.059 MHz. 
>  Because of the capacitors and other circuit loading of the crystals in the circuit
>  tend to move the actual frequency lower, the BFO winds up needing to be around
>  11.055 MHz to allow enough received signal through the 3.0 or so KHz wide filter.

11.059mhz is the nominal parallel resonant frequency of the crystals
The series resonant frequency (as used in the crystal ladder filter) is a few khz lower.

The old Bitx40 made use of this, the BFO oscillator used the 12mhz crystal in parallel resonant mode,
and happened to wind up at just the right frequency down from the 12mhz IF filter.
All those crystals were first sorted to be within 100hz or so of each other before stuffing.

We still need a way to measure the passband of a uBitx IF filter
using the Si5351 as a signal generator and a diode RF detector (or AD8307) getting read
by a Nano ADC pin.  Plot the results on a host computer using the Arduino IDE's "Serial Plotter".
    https://groups.io/g/BITX20/message/32628
    https://groups.io/g/BITX20/message/32630

Jerry


On Sun, Jan 5, 2020 at 09:05 AM, Jim Sheldon wrote:
Since receiving my V6 uBITX a couple weeks ago and having to fix some errors in the original program code, when I compiled and uploaded the program to the Raduino's NANO, it reset both the frequency and BFO calibration frequencies to the factory default code.

After quite a bit of playing with it, I finally figured out just how it worked and got it square in my head where on the filter passband it should be set to have the correct sidebands when selecting CW/USB/LSB.

The uBITX is an "upconversion" radio where the incoming signal is first converted to the 45 MHz first IF frequency and then mixed with the VFO (clock) signals out of the Si5351 chip on the Raduino to select whether the radio is in SSB or CW mode and which sideband you want to listen to (in either mode).  Since the radio is an UP and then back Down conversion, the sidebands wind up being inverted relative to the filter, so the initial BFO setting MUST be set fairly down the LOWER frequency side of the filter (this actually generates and receives USB before being massaged by the USB/LSB selection routines.

The V6 has a nominal Crystal Filter (IF) frequency of 11.059 MHz.  Because of the capacitors and other circuit loading of the crystals in the circuit tend to move the actual frequency lower, the BFO winds up needing to be around 11.055 MHz to allow enough received signal through the 3.0 or so KHz wide filter.

In my actual experience with both a V5 and a V6 uBITX I've found that a good starting point for calibrating the BFO properly is 11.055.0 MHz as indicated on screen in the BFO calibration routine.  That won't be a perfect setting as each uBITX filter will be slightly different, but should produce usable audio to work with for final tweaking of the frequency.  When you get it set to your satisfaction, BE SURE TO WRITE THIS FREQUENCY DOWN before exiting the calibration routine because as the code is currently written, every time you enter the BFO set menu, it resets the BFO frequency to the factory default which is pretty far off what it really needs to be (in every uBITX I've built and I've built over 10 of them from the V3's to now the V6).

I decided to post this so maybe some of the newer people might have an easier time calibrating their BFO's if they wind up having to re-load the software as each reload sets the frequencies back to the factory defaults which can be pretty far off depending on the actual tolerances of the components in the uBITX filter as built - caused by variations in the individual crystals, capacitors, coils etc., used in that filter.  Each radio WILL be enough different that one frequency will not fit all.

Hope this helps a bit.  Took me a while to get it square in MY mind and I've been doing this stuff since 1963 - LOL.

Jim Sheldon, W0EB
TSW Project Coordinator