HDSDR:- Receiving Digimodes Basics. "VAC" and Equivalents.


     

  For beginners I describe here how to use an SDR receiver and HDSDR (or any other SDR program) for basic data decoding. Various methods must be used depending on the SDR and what sound systems you have available on your computer. I assume you are familiar with HDSDR (or the SDR program you are using) and have setup you SDR RX or RX/TX for normal operation. I hope this page will give a start, HDSDR offers much more. Look at the bottom of this page for links to more advanced topics.



First you will need an intermediate sound interface to send audio to a data decoding program.
Determine whether your system supports "Stereo Mix" or it's equivalent maybe called "What You Hear" or something else. If not, consider the other three options. 



In general, any soundcard datamode program may be connected by one of the ways shown. 
Many of the modes listed here http://www.rv3apm.com/ may be used. I have used SSTV, WSJT and APRS packet for my examples because I know where to look and that signals are often available.

For HDSDR settings I suggest using the default filter bandwidth. NR should be off, NB RF + IF should also be off, AGC should be set to Slow,  Squelch should be turned off.

It is best, but not essential, if you are familiar with the SDR program and the datamode program before you try connecting them.

Note:- You may have to match the sample rates in the Audio Properties and software. For example when I was running HDSDR and "What U Hear" to WSPR-X I had to set HDSDR's output to 48,000 before it decoded.


Below I show some examples, note that any SDR that works with HDSDR may be used. 

Using a Funcube Dongle with Stereo Mix to receive packet/APRS, default connection to Ui-View. HDSDR-FCD-UZ7HO-PKT-StereoMix

Using a Soundcard SDR with Stereo Mix  HDSDR-MMSSTV-Stereo Mix-t

Using a Soundcard SDR with VBcable. HDSDR-MMSSTV-VB-Audio-t

Using a Soundcard SDR with VAC HDSDR-MMSSTV-VAC48K-t

Using Stereo Mix with an RTL dongle, Funcube Dongle, or any SDR with an included soundcard or one that sends an IQ stream. I show a more complex setup here using AGW Packet Engine and Ui-view for APRS receive. HDSDR-AGW-Ui-View-c2

Using VAC with a RTL dongleFuncube Dongle, or any SDR with an included soundcard or one that sends an IQ stream. Receiving WSJT HDSDR-GB3VHF-WSJT-JT65B

RDS Spy and HDSDR http://www.apritch.myby.co.uk/radioprop_hdsdr_rdsspy.htm Use a wideband SDR and decode RDS without a 192ksps soundcard.

Please note many of these modes offer a lot more than I show here. These examples are just to get you started. If you have a SDR transceiver then you may setup HDSDR to transmit. Or it is possible to use HDSDR to simultaneously operate your conventional transceiver. Links to a few examples of  these sort of options at the bottom of this page.
This shows A Funcube dongle (FCD)  connected to a soundcard packet terminal by UZ7HO  
 http://uz7.ho.ua/packetradio.htm (Read the help file, in one of the zips is soundmodem.exe, it just runs, no installation) receiving APRS on 2 metres. To show maps just starting Ui-view should be enough, the default values send the data to that program. 

Click on picture for a large image in a new window. This is an example. A SDR containing an internal "soundcard", a RTL dongle or any IQ streaming SDR can all be connected in this way. A soundcard SDR will need an extra soundcard, stereo mix will not work with a card taking the receiver's IQ. Also any digimode expecting an audio input may be connected.

 The FCD has it's own internal "soundcard" HDSDR is set to receive IQ from that. The output from HDSDR is set to The Realtek which has "Stereo Mix". The digimode program is set to this and stereo mix selected in the mixer. 



HDSDR-MMSSTV-Stereo Mix
This shows a soundcard SDR receiving SSTV the audio fed To MMSSTV with stereo mix.

Click on picture for a large image in a new window.  This is an example. A SDR containing an internal "soundcard", a RTL dongle or IQ streaming SDR can all be connected in this way. The soundcard SDR needs an extra soundcard, stereo mix will not work with the card that takes the receiver's IQ. Also any digimode expecting an audio input may be connected.

This is similar to the FCD above except that an extra soundcard is required. HDSDR is set to receive IQ from that. The output from HDSDR is set to The Realtek which has "Stereo Mix". The digimode program is set to this and stereo mix selected in the mixer. 

HDSDR-MMSSTV-VB-Audio
This shows a soundcard SDR receiving SSTV. The audio is fed to MMSSTV via VBCable.

Click on picture for a large image in a new window. This is an example. A SDR containing an internal "soundcard", a RTL dongle or IQ streaming SDR can also be connected in this way. Any digimode expecting an audio input may be connected. 

Here the audio is sent to the digimode program with VB-Audio. No speaker output is available.



VAC HDSDR-MMSSTV-VAC48K
This shows a soundcard SDR receiving SSTV with the audio fed to MMSSTV with VAC.

Click on picture for a large image in a new window.  This is an example. A soundcard SDR, a SDR containing an internal "soundcard", a RTL dongle or IQ streaming SDR can also be connected in this way. Any digimode expecting an audio input may be connected. 
VAC is like VB-Audio, but more versatile. Audio is sent to the digimode program with VAC, the Audio Repeater incorporated with VAC can pass the audio to the speaker soundcard as well.


Showing AGW Packet Engine and Ui-View using a RTL Dongle and Stereo Mix.

Click on picture for a large image in a new window.  This is an example. A SDR containing an internal "soundcard", a RTL dongle or IQ streaming SDR can all be connected in this way. A soundcard SDR will need an extra soundcard, stereo mix will not work with a card taking the receiver's IQ. Also any digimode expecting an audio input may be connected. 

With IQ streaming SDRs like the RTL dongle HDSDR's Soundcard RX input is not used. Here audio is sent to the digimode program with stereo mix and it is selected in the mixer panel.

Click on picture for a large image in a new window.  This shows a RTL dongle with HDSDR Receiving JT65B with VAC. Here the beacon GB3VHF on 144.430 exactly (within a few parts in 10-12  long term) is shown. Details here http://gb3vhf.co.uk/GB3VHFReceiving.html  WSJT  http://www.physics.princeton.edu/pulsar/K1JT/
VAC is selected in HDSDR's RX Output. WSJT requires you to look at the "DOS" window to see the number Windows allocates to VAC and enter it in the setup.
As in most HF digimodes USB is selected. Tuning is 1.5KHz below the actual digimode frequency. This is required by many digimode programs so that audio tones centred on 1.5KHz are sent to the decoder. Read the program's help files.





This method applies to all SDR software, not only HDSDR

1)Stereo Mix 

For passing audio in one direction from one program to another:- Many soundcards have a "Stereo Mix" , "What You Hear" , maybe some other name in their mixer settings. This is said to be often available but hidden.

Set HDSDR "RX Output (Speaker)" to the card with Stereo Mix. Set the digimode program to the input of that card and select Stereo Mix in the soundcard mixer. Note that soundcard SDRs must use a different card for the IQ input. 

Information
A lengthy description and discussion about "Stereo Mix" here.
Note it is not always available. If you can install a second card then there is a good chance it will have this facility.
If a sound system has been automatically installed by Windows then using the manufacturer's installation disc may also install Stereo Mix. (Often along with much other unwanted enhancements.)

2) VB Cable
 http://vb-audio.pagesperso-orange.fr/Cable/index.htm One cable free, more by donation. One is all you need for receive.. I have not read too many reports about this, it has worked for me but some have suggested it does not always work.

You will have no speaker output. Set HDSDR "RX Output (Speaker)" to "VB Audio Point". Set the digimode input to "VB Audio Point".

3) Another possibility is to link two soundcards by  a real cable. I have not tried this. Although it is not usually recommended some have reported good results. A USB device may be used, preferably of reasonable quality.

You would have to Set HDSDR "RX Output (Speaker)" to one card. Set the digimode input to the other. Connect the Line Out (Speakers) of the first to the Line In of the second. I guess speakers may be connected to the second card.

4) Virtual Audio Cable

Virtual Audio Cable is used to send audio streams between HSDR and another program  http://software.muzychenko.net/eng/vac.html This is not free (From 25USD). There is a demonstration for initial testing but DO NOT USE THIS FOR TRANSMITTING. A voice message is superimposed on the audio stream.

Only one cable is needed for receive. Set HDSDR "RX Output (Speaker)" to Virtual Cable 1. Set the digimode input to Virtual Cable 1. The VAC Audio Repeater may be used to send audio to the speakers.

 NOTE some time ago when I was first setting up Virtual Cable it took several seconds, the screen blanked, I thought there were serious problems! However, no damage was done! 
 
Select one cable, Click "Set" to install. (Or

more cables if you have a specific requirement) The default settings above have always worked with me but you may find it necessary to increase the Sample Rate (SR) range for applications that require higher, or lower, rates.

I have found this program able to be set and forgotten.
VAC appears as a soundcard in Windows and HDSDR's sound menu.

In the Windows Start Menu is the "VAC Audio Repeater" which enables the VAC stream to be passed to a speaker output.



"Donationware" Voicemeeter is said to be able to stream audio from one source to two others so the received audio can be heard. http://vb-audio.pagesperso-orange.fr/Voicemeeter/index.htm


A page showing more detail and advanced setups https://sites.google.com/site/g4zfqradio/hdsdr_digi-modes


HDSDR PAGES
As a Panadaper with Tuneable SDR:- Using an Ensemble with a conventional transceiver as a panadaptor. My preferred way for HF. Ideally take the Ensemble antenna connection from the transceiver.
Using as an IF Panadapter.  with a conventional receiver or transceiver. 
Using HDSDR with a RTL dongle 
https://sites.google.com/site/g4zfqradio/hdsdr-use-with-rtl-dongle And using the dongle as an IF panadaptor with a conventional rig.

G4ZFQ August 2013







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