What form is IQ VAC?

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Buck
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What form is IQ VAC?

Postby Buck » Wed Aug 23, 2017 7:16 pm

When I output the audio through M-VAC, it is, I think, a AM modulated and digitally sampled waveform. If I click Direct IQ output to VAC, what form does the data take?

Buck ko0y
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w-u-2-o
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Re: What form is IQ VAC?

Postby w-u-2-o » Wed Aug 23, 2017 8:11 pm

The normal sound output is not AM modulated, it is just plain old demodulated audio. Of course it is digitally sampled, at the sample rate specified in the VAC1 control screen. I believe the resolution is 16 bits.

When you select IQ output you get I on the left channel, Q on the right, at the sample rate specified. Again, I believe the resolution is 16 bits. This often known as the "Softrock-IF" format.

If you are using 192KHz as your primary sampling rate, and select 192KHz for the VAC IQ output, and are using software compatible of processing that IQ stream at that speed in the Softrock-IF format, then you will see the same information in the external software application as you do on your PowerSDR mRX panadapter. I believe that CW Skimmer can do this.

73,

Scott
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DL2XY
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Re: What form is IQ VAC?

Postby DL2XY » Fri Nov 17, 2017 3:03 pm

w-u-2-o wrote:When you select IQ output you get I on the left channel, Q on the right, at the sample rate specified. Again, I believe the resolution is 16 bits. This often known as the "Softrock-IF" format.


Is there any way to transmit I/Q via VAC?

73 Walter
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w-u-2-o
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Re: What form is IQ VAC?

Postby w-u-2-o » Fri Nov 17, 2017 3:41 pm

I don't know! Interesting question. Is there any software that generates IQ like that?
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DL2XY
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Re: What form is IQ VAC?

Postby DL2XY » Sat Nov 18, 2017 9:27 am

There are at least two programms i know, Multipsk and Dream DRM.
But my main interest would be the use of IQ-TX in my own DSP programming experiments.

73 Walter
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w-u-2-o
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Re: What form is IQ VAC?

Postby w-u-2-o » Sat Nov 18, 2017 2:40 pm

DL2XY wrote:There are at least two programms i know, Multipsk and Dream DRM.
But my main interest would be the use of IQ-TX in my own DSP programming experiments.

Walter,

AFAIK, MultiPSK and Dream only receive IQ, they do not transmit it.

Looking carefully at the PowerSDR settings, it does not seem like it can accept an IQ stream for transmission via VAC, however you would have to inspect the source code to be sure. Since you are a programmer that might be the best thing for you to do. Source is available at the TAPR repository, of course.

73,

Scott
Bryan W4WMT
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Re: What form is IQ VAC?

Postby Bryan W4WMT » Sat Nov 18, 2017 8:22 pm

Passing raw TX IQ data through VAC1 would be easy, a no-brainer.
But what do you do with it when it arrives upstream at WDSP?
That’s a different matter altogether.

73
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DL2XY
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Re: What form is IQ VAC?

Postby DL2XY » Sun Nov 19, 2017 4:18 pm

w-u-2-o wrote:AFAIK, MultiPSK and Dream only receive IQ, they do not transmit it.


Scott,

I'm not sure about IQ-tx in Multipsk (IQ-rx is supported) , but Dream definitly can.
Just start it "dream -t" to get in tx-mode.

dream_config.jpg
dream_config.jpg (68.64 KiB) Viewed 3589 times


This is a 10kHz wide DRM signal output by Dream displayed with one of my diy-tools via VAC.
By the way, this ist a hard test for Puresignal, the 20kHz version is nearly impossible to transmitt with reasonably low IMD.

dream_output.jpg
dream_output.jpg (70.71 KiB) Viewed 3589 times


Of course I have already examined the sources, but they are huge and sparsely commented...
Maybe someone can recommend an free IDE running on WIN-XP to build the project ?

73 Walter
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w-u-2-o
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Re: What form is IQ VAC?

Postby w-u-2-o » Sun Nov 19, 2017 4:24 pm

Very cool, Walter. I did not realize you could be your own DRM format pirate radio ;)

Maximum conventional TX SSB bandwidth in PowerSDR mRX is 20KHz. If you can get that to work with DRM, I'd recommend using "single calibrate" mode in PureSignal with the two-tone signal centered in the 20KHz passband. This is not difficult, as you can go to Setup > Tests and adjust the two-tone test freq's to be say 10070 and 10190KHz.

73!

Scott
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Re: What form is IQ VAC?

Postby Bryan W4WMT » Sun Nov 19, 2017 9:50 pm

Hi Walter,

The developers are currently using Visual Studio 2013 Community, which is a free download from Microsoft.
The existing VAC1 code (see audio.cs) should handle IQ transmit streams just fine without modification. But I believe you would have to develop a WDSP block to pass the IQ data upstream to the DUC running in the FPGA. Have you seen NR0V’s video tutorial on WDSP and also the Wdsp documentation manual?

73
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DL2XY
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Re: What form is IQ VAC?

Postby DL2XY » Sat Nov 25, 2017 11:21 am

Hi Bryan,

Many thanks for your advise.

Finally i wangled to get VS up and running...

First builds look promising.
My "personal Edition" now supports IARU Region1 60m Band definition without the need to use the "Extended" Region setting.

73 Walter [DL2XY]

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