To clarify:
My solution would be to use the non-standard tone spacings on the air and
resample the Rx audio inside my rig to 48 kHz before sending to WSJT.
should have said that the external resampling would include timebase scaling to
bring the received tone spacings back to the standard.
----- Original Message -----
From: "Mike Lavelle" <[email protected]>
To: "WSJT software development" <[email protected]>
Sent: Wednesday, March 14, 2018 3:31:30 PM
Subject: Re: [wsjt-devel] audio interface
Thanks for confirming that, Joe.
The reason for my question is that I have built a millimeter wave radio using
technology that cannot be linearly modulated.
I can receive any modulation, but on transmit I can only send CW or angle
modulation (BPSK, BFSK or one-of-MFSK).
Here are a couple of ways that I can think of using the WSJT protocols with
such a rig:
Present a USB audio interface that appears to be a 48 kHz, 16 bit mono stream
to/from WSJT.
On Rx, things appear to be normal: The CAT interface tunes in the signal. SSB
down converts to audio and we let WSJT do it's thing.
On Tx, one of two options:
(1) Does/could WSJT have an option to command a Tx frequency synthesizer on a
per tone basis over the serial interface to the rig? Instead of sending audio
tones, just send tone numbers and let the synth shift to the new tone. Murray,
ZL1BPU, offers this option in his WSQ2 mode (SSB exciter vs Synthesizer modes).
(2) Let WSJT send audio tones to the mmwave radio via USB. Add firmware to the
rig to do tone frequency detection and offset the Tx frequency synthesizer by
the tone frequencies.
My Tx frequency synthesizer can be programmed in steps of 10.000000 MHz /
2**-N, (9.536743 Hz).
So I can't hit the various JT tone spacings on the nose. I could be about 9%
high for most JT4 modes, 11% low for JT65C, and so on.
My solution would be to use the non-standard tone spacings on the air and
resample the Rx audio inside my rig to 48 kHz before sending to WSJT.
What do you think? Any better ideas?
73,
Mike, K6ML
----- Original Message -----
From: "Joe Taylor" <[email protected]>
To: "WSJT software development" <[email protected]>
Sent: Wednesday, March 14, 2018 2:43:13 PM
Subject: Re: [wsjt-devel] audio interface
On 3/14/2018 5:13 PM, Mike Lavelle K6ML wrote:
> In WSJT-X, the sound card sample rate is always 48000 Hz and 16 bits,
> regardless of the mode (JT4, JT9, ISCAT, JT65, FT8, etc) selected?
Correct.
> The protocol descriptions mention 11025 and 12000 sample rates for
> various modes, so I can assume that the sample rates are converted
> within WSJT-X?
Resampling or "downsampling" is done many times in the chain of DSP
steps leading up to the actual decoder. These steps (which may overlap
somewhat, depending on the mode) include signal detection,
synchronization, and demodulation. Downsampling eventually ends at the
mode's symbol (or keying) rate. For WSJT slow modes these rates are
1.46 to 6.25 Hz, see Table 4 here:
http://www.physics.princeton.edu/pulsar/K1JT/wsjtx-doc/wsjtx-main-1.9.0-rc2.html#PROTOCOLS
The protocol descriptions mention 11025 and 12000 Hz because these rates
help to define exactly how the codecs are designed. They are convenient
rates at which to describe the modes, but not requirements.
-- 73, Joe, K1JT
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