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Please explain to me how works the VFO's


Gerard
 

hello,

I re-checked the pcb. The cabling is correct.
For me, there is only one solution: Replace the 2n3904. they may be of poor quality. I don’t have a bfr at my fingertips, but I’m going to do a test with 2n2222.

cdt


Gerard
 

Hello,

i have made all the tests possibles on the hardware
1) Tested with frequency generator the first stage of amplificator (3 transistors) >>Ok
2) tested the second stage of amplificator (also 3 transistors)  >>ok
3) Tested the 45MHZ filter, the best signal is at 45007680 Htz >>> Delta of 7680Htz so tolerance of 0.0017%  >> Good for me
4) Tested the squale filter 12MHZ (I have 12MHZ crystal)  >>Best signal at 11.988370Htz Delta 11630htz (Quality of quartz)  >> good for me
5) tested the amplifier  >> ok

so some calculation:
The best LSB frequency will be of 56996050Htz  (56996050 - 11988370 =45007680
The best USB  frequency will be of 33019310Htz  (33019310 + 11998370 =45007680
When i calibrate the BFO, is good the low beat is exactly at 11998370  >> i thing it's good.
But when you made calibration, the zero beat is done too fast, just a few rotation movements. the sound also seems slightly more strident.
Frequency can by ajust at 33019310, I CAN't GO more  HIGHER in frequency. (EXmax 35 mhz)
I don't know how is made this calibration (On 33 or 56mhz)
THE PB in the recption:
When i put a counter, to be LSB or USB, frequency seem be the same.(Clock1)
The frequency of clock 0 seem also less....

All this to ask you if what is below is normal or not.
look on at the beginning of SI5351 code: (It's the same on V3, V6 for example)
 
#define BB0(x) ((uint8_t)x)             // Bust int32 into Bytes
#define BB1(x) ((uint8_t)(x>>8))
#define BB2(x) ((uint8_t)(x>>16))
 
#define SI5351BX_ADDR 0x60              // I2C address of Si5351   (typical)
#define SI5351BX_XTALPF 2               // 1:6pf  2:8pf  3:10pf
 
// If using 27mhz crystal, set XTAL=27000000, MSA=33.  Then vco=891mhz
#define SI5351BX_XTAL 25000000          // Crystal freq in Hz
#define SI5351BX_MSA  35                // VCOA is at 25mhz*35 = 875mhz

Should lines not be unlocked? like the definition of the crystal?
I have a SI5351 module (Cristal 25mhz) plugged into my main PCB. Does the app match?
I think the reception pb is there, following misalignment.

When do you think of all that?

cdt


Evan Hand
 

On Tue, Sep 15, 2020 at 10:09 AM, Gerard wrote:
When i calibrate the BFO, is good the low beat is exactly at 11998370  >> i thing it's good.
This may be where you are off.  What you calculated was the center frequency of the SSB filter if it was actually 12MHz.  The capacitors in the filter shape and lower the filter frequency.  Since those can vary in tolerances, the actual amount of shift varies from board to board.  Most would be between 1700 and 1800 lower.  You would need to run a scan on the filter to find the actual value (a NanoVNA or Antuino are good tools for that). 

The audio signal is 3kHz wide, so you need to subtract half of that or 1500 so that the BFO would be set at 12000000-1750-1500=11996750  That is very close to the BFO setting that I have for one of my v4 uBITX with a 12MHz SSB filter (11.996795).

The code should work with the SI5351 module and the 25MHz crystal setting.

Try adjusting the BFO to the 11996795 value and see if that helps.  Also, I would remove the AGC circuit from the rig at this time so that it is not limiting the audio to the amp.

Just suggestions.
73
Evan
AC9TU


Gerard
 

On Tue, Sep 15, 2020 at 08:26 PM, Evan Hand wrote:
The code should work with the SI5351 module and the 25MHz crystal setting.

Try adjusting the BFO to the 11996795 value and see if that helps.  Also, I would remove the AGC circuit from the rig at this time so that it is not limiting the audio to the amp.

Just suggestions.
73
Evan
AC9TU

 

 


From: Gerard <kabupos@...>

 
 
 
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Gerard
 

hello Evan,
Thanks for your advice.
I had some idea that the code was good, otherwise no µBitx could work.

To night the spread seemed better (?). I caught Russians, Italians, etc
The sound was much louder, but still a bit distorted. You must play on the cursor of the pictogram representing the curve of the filter to improve.
I had recalibrated with a generator, but it makes a pure carrier and must distort the result. i will ask a French ham, if there is a reference transmitter.
In this case, i will test  this:
https://petetest2017.files.wordpress.com/2019/01/micro-bitx-calibration-instructions.pdf
I’ll also redo a good antenna. That’s 80% of the reception.

cdt