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New audio output "device".

Gullik Webjorn
Hi all,

We are learning more and more, and today we have a nice small receiver
(remotetrx) based on a orange pi zero and a dorji dra808 / 818

The radio addon is a piece of pcb stacked on top of the OPZ, and we are
using noise detect which works quite nice.

The TX we want to use is based on a low cost dds, actually a ad9850
board from ebay, and we are going to use the 1st alias, which can be
around 108 mhz, and thus contains some  energy, and multiply by four to
get to the final QRG.

Now I am looking at interfacing the dds to svxlink, ( actually
remoteterx ) and would need the internal digital data to send to the dds
program.

The dds program will modulate 1.25 khz ( fout/4) so the resulting signal
can be injected in the apropriate stage of an old UHF repeater transmitter.

I understand svxlink uses 8 khz for internal sample rate, and 16 bit
signed integers for data, thus I would

want to receive exactly that, and scale those integers to +/- 42955 to
be added to the DDS frequency value which would result in exactly +/- 5
khz at final QRG.

Suggestions how to achive this welcome, and fell free to correct my
assumptions.

73 de SM6FBD



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Re: New audio output "device".

Rob Janssen
Gullik Webjorn wrote:

> The TX we want to use is based on a low cost dds, actually a ad9850
> board from ebay, and we are going to use the 1st alias, which can be
> around 108 mhz, and thus contains some  energy, and multiply by four to
> get to the final QRG.
>
> Now I am looking at interfacing the dds to svxlink, ( actually
> remoteterx ) and would need the internal digital data to send to the dds
> program.
>
> The dds program will modulate 1.25 khz ( fout/4) so the resulting signal
> can be injected in the apropriate stage of an old UHF repeater transmitter.
>
> I understand svxlink uses 8 khz for internal sample rate, and 16 bit
> signed integers for data, thus I would
>
> want to receive exactly that, and scale those integers to +/- 42955 to
> be added to the DDS frequency value which would result in exactly +/- 5
> khz at final QRG.
>
> Suggestions how to achive this welcome, and fell free to correct my
> assumptions.
>
> 73 de SM6FBD
>

Interesting idea!
Actually the internal sample rate is 16 kHz and the sample rate at the external
interfaces can be user-configured using CARD_SAMPLE_RATE which can be
16 or 48 kHz.  Unfortunately this is a global option so you cannot set this exclusively
for your transmit interface.

You are correct that the sample format is 16-bit signed integers. The actually used
range is usually only about 1/3 of the maximum, to allow the processing of
"unsquelched audio" without overdriving the A/D.  See the calibration procedure.

Rob

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Re: New audio output "device".

Gullik Webjorn
Fine,

I have no problem whatsoever with 16 khz, in fact I was actually
contemplating upsampling

to achieve some "modulation filtering". Also, given that there is
restrictions on the

waveform limits within the sample, well that is only a constant to
multiply before adding

to the DDS. This is also Version 1.0 of the TX, built with readily
available parts, locking the

ref oscillator of the dds to a gps would allow "single freq multi tx".
But these can be added as

we move on.....

No how do I access the 16 bit samples at 16 khz in the simplest way?

A pipe? ( no support for an audio pipe in svxlink), is there not some
thing like a "virtual sound card"? I.e. a program-program interface that
might already be there ??

73 de SM6FBD


On 2017-05-01 21:17, Rob Janssen wrote:

> Gullik Webjorn wrote:
>> The TX we want to use is based on a low cost dds, actually a ad9850
>> board from ebay, and we are going to use the 1st alias, which can be
>> around 108 mhz, and thus contains some  energy, and multiply by four to
>> get to the final QRG.
>>
>> Now I am looking at interfacing the dds to svxlink, ( actually
>> remoteterx ) and would need the internal digital data to send to the dds
>> program.
>>
>> The dds program will modulate 1.25 khz ( fout/4) so the resulting signal
>> can be injected in the apropriate stage of an old UHF repeater transmitter.
>>
>> I understand svxlink uses 8 khz for internal sample rate, and 16 bit
>> signed integers for data, thus I would
>>
>> want to receive exactly that, and scale those integers to +/- 42955 to
>> be added to the DDS frequency value which would result in exactly +/- 5
>> khz at final QRG.
>>
>> Suggestions how to achive this welcome, and fell free to correct my
>> assumptions.
>>
>> 73 de SM6FBD
>>
> Interesting idea!
> Actually the internal sample rate is 16 kHz and the sample rate at the external
> interfaces can be user-configured using CARD_SAMPLE_RATE which can be
> 16 or 48 kHz.  Unfortunately this is a global option so you cannot set this exclusively
> for your transmit interface.
>
> You are correct that the sample format is 16-bit signed integers. The actually used
> range is usually only about 1/3 of the maximum, to allow the processing of
> "unsquelched audio" without overdriving the A/D.  See the calibration procedure.
>
> Rob
>
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> Check out the vibrant tech community on one of the world's most
> engaging tech sites, Slashdot.org! http://sdm.link/slashdot
> _______________________________________________
> Svxlink-devel mailing list
> [hidden email]
> https://lists.sourceforge.net/lists/listinfo/svxlink-devel


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Re: New audio output "device".

Rob Janssen
Gullik Webjorn wrote:
> No how do I access the 16 bit samples at 16 khz in the simplest way?
>
> A pipe? ( no support for an audio pipe in svxlink), is there not some
> thing like a "virtual sound card"? I.e. a program-program interface that
> might already be there ??
>

Yes, look at the "loopback" audio interface in Alsa.
It is being discussed here recently and an explanation how it works can be found
in the example of internet streaming on the WiKi.

Rob

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