DATV-Express SSB / FM Radio Transmitter

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G4GUO
Posts: 728
Joined: Tue Feb 16, 2010 12:51 pm

Re: DATV-Express SSB / FM Radio Transmitter

Post by G4GUO » Mon Dec 03, 2018 1:17 pm

I suspect there is a work around I will have to check first.

The work around would be to calibrate the Express board using the DATV App
then copy the calibration from the configuration file into the SSB configuration file.

The other issue may well be the frequency stability of the Express board at 2.4 GHz.

The TX frequency is controlled by a 20 MHz SMD oscillator on the board.

On one of my units I have replaced the oscillator with an SMA so I can use
an external GPSDO.

http://g4guo.blogspot.com/2016/06/coupl ... -datv.html

- Charles

G4GUO
Posts: 728
Joined: Tue Feb 16, 2010 12:51 pm

Re: DATV-Express SSB / FM Radio Transmitter

Post by G4GUO » Mon Dec 03, 2018 1:41 pm

Yes it does look like that work around would work, here below is the contents of the configuration file for ExpressSDR

# Automatically updated, one space between parameters
set af 21
set rf 36
set freq 2400100000
set mode usb
set mic Microphone (HD Pro Webcam C920)
set fcor 1.000002400000
set ioff 0
set qoff 0

Here are the lines from Express DATV


-21
[Q DC OFFSET] -39


Once the Express board is up to temperature the values shouldn't change much.

For some reason the forum is mangling the Express OFFSET part of my post (bad forum)

- Charles

ON7KGK
Posts: 9
Joined: Mon Feb 15, 2016 8:47 am

Re: DATV-Express SSB / FM Radio Transmitter

Post by ON7KGK » Mon Dec 03, 2018 3:46 pm

thank you a lot Charles ;) ;) ;)
I will try this evening.

ON7KGK
Posts: 9
Joined: Mon Feb 15, 2016 8:47 am

Re: DATV-Express SSB / FM Radio Transmitter

Post by ON7KGK » Mon Dec 03, 2018 7:52 pm

Perfect it works correctly with the values you have done.
Thank you a lot Charles !

G4GUO
Posts: 728
Joined: Tue Feb 16, 2010 12:51 pm

Re: DATV-Express SSB / FM Radio Transmitter

Post by G4GUO » Mon Dec 03, 2018 7:54 pm

That is interesting I was expecting every board to need unique values :oops:

- Charles

G4GUO
Posts: 728
Joined: Tue Feb 16, 2010 12:51 pm

Re: DATV-Express SSB / FM Radio Transmitter

Post by G4GUO » Tue Dec 04, 2018 8:34 am

I experimented with it last night and it seems the calibration is frequency dependent
so for best carrier suppression it needs to be calibrated near the operating frequency.

Eventually I may add code so it can store multiple calibration points and when a frequency
is selected it chooses the closest one.

- Charles

ON7KGK
Posts: 9
Joined: Mon Feb 15, 2016 8:47 am

Re: DATV-Express SSB / FM Radio Transmitter

Post by ON7KGK » Tue Dec 04, 2018 6:31 pm

It will be a nice improvement indeed if you could add this feature.
Best 73's

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