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forum.funcube.org.uk • View topic - What is the best decode frequency for a SSB radio

What is the best decode frequency for a SSB radio

For the early roll-out of the Dashboard

Moderator: pa3weg

What is the best decode frequency for a SSB radio

Postby WB4SON » Fri Nov 22, 2013 3:48 am

My radio only supports fairly narrow bandwidths (up to 3.6 KHz).

I was wondering what I should adjust the beacon to in terms of decode audio frequency.

In my case I set my downlink to 145.935.760, and I was getting a decode frequency around 1000 HZ.

Thanks!

73, Bob, WB4SON
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Re: What is the best decode frequency for a SSB radio

Postby g0mjw » Fri Nov 22, 2013 7:11 pm

I am puzzled by the decode frequency when using the funcube dongle. I am receiving at 59kHz according to the scale on the plot but 11kHz according to the frequency display. Now assuming the centre frequency of 144.925 MHz is showing as 48kHz this makes sense but isn't all that clear. The graph of decode frequency vs time is great for looking at the Doppler. All the blue links on the realtime page are to graphs in case you had not noticed.

It would be nice if the actual RF frequency could be displayed.

Mike
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Re: What is the best decode frequency for a SSB radio

Postby Duncan » Sat Nov 23, 2013 6:11 pm

Yes sorry about that... the scaling on the graph was one of those features that just didn't make it for launch, I will be trying to address that and a whole load of other things over the coming days...
Just displaying the RF frequency is one of those things that seems easy on the face of it but is actually a bit more involved... Scaling the graph at the start is easy just read FCD frequency then +-48kHz, done, but then what do you do if something else (SDR Sharp etc...) re-tunes the dongle, so you have to continually monitor the dongle freq and adjust the scale, but then you also have to adjust the auto tune range, but that is based on FFT bucket position not absolute frequency so you have to convert etc...

So for now, the the frequency display as you have figured, displays 0-96kHz which is the bandwidth of the input, (I know FCD+ can do 192) and puts the FCD centre frequency at 48kHz, to then further confuse the value reported as "Decode Frequency" is -48k to +48k with 0 as the FCD centre frequency.

Cheers,
Duncan.
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Re: What is the best decode frequency for a SSB radio

Postby VK2FBRB » Sat Nov 23, 2013 6:46 pm

You've done a great job Duncan. For unattended decoding via FCD+, I set Low: 53000, High: 63000, and let it work its magic in the background.

For soundcard capture with a couple of kHz of bandwidth, is there any performance benefit in reducing the Auto-Tune Range as opposed to leaving it full spectrum?

Eg, Bob's 3,600 Hz bandwidth - any point in setting his Auto-Tune Range to Low: 0, High: 4000?

soundcard_bandwidth_auto_tune.jpg
soundcard_bandwidth_auto_tune.jpg (59.58 KiB) Viewed 9095 times


Thanks,
Ben VK2FBRB
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Re: What is the best decode frequency for a SSB radio

Postby Duncan » Sun Nov 24, 2013 11:52 am

Not a huge benefit no, you may find when using an 817 or similar, and sound card input, the best way of decoding is to turn off auto tune and fix the decoding frequency to 1200hz. You can then tune the receiver trying to keep the "rock horns" equally spaced on either side of the line.
We have discussed making this another capture mode/audio setting, whereby selecting it automatically restricts the spectrum display to between 0-5000Hz and expands it to fill the display. This would show more detail and hopefully make tuning easier.
Please let us know what you think, suggestions for features are always gratefully recieved...

Cheers,
Duncan.
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Re: What is the best decode frequency for a SSB radio

Postby WB4SON » Sun Nov 24, 2013 1:13 pm

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Re: What is the best decode frequency for a SSB radio

Postby g0mjw » Sun Nov 24, 2013 2:55 pm

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Re: What is the best decode frequency for a SSB radio

Postby Duncan » Tue Nov 26, 2013 11:23 am

A waterfall display is something to consider, although I always fire up SDR# and just use that...

I don't think impossible, when using a dongle, there is nothing stopping us (apart from CPU power) from firing up multiple decoders at multiple frequencies, currently the dashboard uses three, one at the detected centre frequency and one on either side (just in case it's a little bit off). Future versions could easily put decoders at all the detected peeks and lock onto any that decode.

Cheers,
Duncan.
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