I'm not sure what your frequencies mean. 11994420 - 11984800 = 12000
and 11996450-11984800 = 9620.
These don't match your 2030hz and 4060hz figures.
If your crystals all average out to about 11984800hz then any bandpass
filter will have a frequency just a little above that frequency. Let's
assume it will run from 2khz to 5khz higher, i.e. a 3khz bandwidth or
from 11986800hz to 11989800hz.
I thought the bitx40 used a 5Mhz vfo and a 12Mhz if (i.e. crystal
filter frequency)?
Why are you adding a 12Mhz (vfo offset) to the frequency? And then using
another 12Mhz (usbCarrier) signal to demodulate it? You just wind back
up with a signal of 7Mhz.
Am I misunderstanding what you are doing?
There is a reason for shifting the vfo frequency. To make the best use
of a crystal filter, which typically has a steeper cutoff at the lowest
frequency and a less steep cutoff at the upper frequency, usually LSB
signals are converted to USB signals where the audio frequencies higher
in frequency than the carrier.
tim ab0wr
On Wed, 14 Mar 2018 01:54:42 -0700
"Ryan Flowers" <geocrasher@...> wrote:
Hello Everyone,
I've been working on my own digital VFO/BFO for my BITX40. The goal:
Switch sidebands without inverting the VFO to 19mhz for 40M and 26mhz
for 20M. I've got it working, mostly, but I'm having one heck of a
time with audio quality. The 12mhz crystals not 12mhz but rather
11,984,800 and currently I have my sidebands at 11994420 for USB and
11996450 for LSB. These are 2030 and 4060hz away from the crystal
frequency, and I am having a hard time visualizing how that works.
But at any rate, these are the what I came up with mostly through
trial and error.?
I'm currently using a modified version of the uBITX sketch. I've
added the offset frequency (11984800, named vfoOffset) and lsbCarrier
and am using the following to do my tuning:
if (isUSB){ si5351bx_setfreq(0, vfoOffset + frequency);
si5351bx_setfreq(1, usbCarrier); } else{ si5351bx_setfreq(0,
vfoOffset + frequency); si5351bx_setfreq(1, lsbCarrier); } I've also
added menu items for adjusting the USB/LSB and Offset easily, and
using these I adjusted for best inbound audio and ended up with the
aforementioned values. When I tune the radio to 7074mhz and select
USB, I'm not getting *any* decodes on FT8- but it works on LSB...
What on earth? The other thing is that audio output (as tested by
transmitting into a dummy load and listening on my Kenwood) is just
terribly choppy and unintelligible. I've tried varying the signal
output strength of the si5351 clocks from 2ma to 8ma, no difference.
It sounds terribly over-modulated.
I have gotten in over my head, but I'm determined. Can somebody help
me understand this so I can not just complete this project but get a
better understanding??Thanks so much.
--?
Ryan Flowers - W7RLF
MiscDotGeek.com ( )
Multi Band BITX40 ( )
The BITX40 FAQ ( )
