Re: uBITx v5 - with mods

Jerry Gaffke
 

Ravi,

Your equations look correct, though this might be a more concise description of the math involved: 
    https://groups.io/g/BITX20/message/44515

That was for a uBitx-v3, so had the 12mhz IF crystals, not 11.052mhz.
Those IF crystals get sorted at hfsignals into bins by frequency such that all crystals
used in any given rig are of the same frequency within perhaps 100hz or better.
Between rigs using crystals from different sorting bins, the 12mhz (or 11.0592mhz)
crystal filter can vary from rig to rig by a khz or so.
Some have found that the rig sounds better if the BFO is moved away
from its factory value by a few hundred hz.

Likewise, the center frequency of 45mhz filter might vary by a few khz,
but it is wide enough that you probably would not notice any reduced sensitivity
or change in audio quality without a direct A/B test.

An RF preamp may be needed to hear much if operating with a short whip.

Several here have played with different si5351 output drive levels and came to
different conclusions.  This can affect signal levels and birdies, but generally isn't critical.
The ideal settings might vary a bit from rig to rig, and your local incoming RF levels. 

Posts 35235 and 54501 describe a calibration procedure that might be of interest. 

Jerry, KE7ER


On Mon, Jun 10, 2019 at 06:09 AM, Ravi Miranda wrote:
Hi Sarma, Farhan, Curt,

Thank you all for replying so quickly. I have carried out the following:


a. I have used KD8CEC v1.20 for uBITx V5
b. The #define has been set for V5
c. I have an approx. 100mV signal now (10MHz) and injected that. On
hearing low output at the output, I proceeded to do the math to
calculate the values at each stage.

Here are the equations used. Assuming USB

1. IF_A_FREQ = VFO FREQ - INP_FREQ [IF_A_FREQ ---- should be a value
of 45MHz so that it can get through the 45 MHz crystal filter
+/-7.5Khz]
2. OP_FREQUENCY = IF_LOCAL_OSC - IF_A_FREQ [OP_FREQUENCY ---- should
be centred on 11.0592 000 (or thereabouts) to get through the Ladder
filter
3. AUDIO_OUT = BFO_FREQUENCY - OP_FREQUENCY [If both match correctly,
we get a ZERO Beat] if the BFO_FREQUENCY > OP_FREQUENCY we get LSB and
the other way we get USB.

Using these calculations, I arrived at a frequency difference of 6660
[strange number if you get the drift :-) ] No pun intended.

With no calibration, I got nothing, not surprising as the frequency was way off.

Using a frequency meter, I set the calibration of the XTAL from
25.000.000 to 25.003.090 (This value was found using
https://groups.io/g/BITX20/wiki/Si5351-Calibration-Sketch)
The pitch of the tone may have changed, not sure at this stage it was very late.

Using the IF Shift menu option I moved the IFShift to 6660, and the
tone was clearly there. [LOUD]

Having set this right (so far), I tried the whip antenna in the
balcony (sorry no dipole). There are no signals to be heard at all. So
I have the following questions.
1. Should I change the VFO base frequency to 45.005.000 (given that
the two inductances at both sides are pulling the crystal filter off?
If so what is the best value to set this to, and where in the program
2. Are the equations above correct
3. Instead of the IFShift of 6600 should I be thinking of changing the
#define SECOND_OSC_USB (56054200l)
#define SECOND_OSC_LSB (33940800l)
to better take into account the shift and therefore bring the shift
(as shown in pt.3 above to 0)
4. To improve reception of signals with my antenna, should I add an RF
preamp prior to the antenna input? This could be switched in via a
relay and not kept in the transmit path (not really sure here as I
haven't managed to test transmit section yet.
5. What are the effects of setting lower or higher current values for
SI5351(2,4,6,8)

Is there a worked example that has
a. BASE_VFO_FREQUENCY
b. USB_FREQUENCY
c. LSB_FREQUENCY
d. BFO_FREQUENCY

I can then use the calibration program to generate these three signals
and do measurements?

Many thanks for taking time to help me with this.

Best 73,

Ravi/M0RVI

Join BITX20@groups.io to automatically receive all group messages.