HDSDR-CWSkimmer and Other Digimodes Using IQ Output or Demodulated Audio.


The main reason for HDSDR to implement the I/Q output is to make it possible to send IQ signals to digimode programs from non-soundcard receivers like RFspace SDR-14/IQ, ELAD FDM-S1 or RTL-Dongles.

This page shows how HDSDR's IQ output feature may be used when software like CW Skimmer is not able to control a SDR directly but can control HDSDR with Omni-Rig. http://www.dxatlas.com/cwskimmer/ 30 day shareware. 

 

Using Other Programs with HDSDR
A similar program is RCKskimmer http://www.walter-dallmeier.de/software-by-dl4rck/rckskimmer/  RCKskimmer is able to search for digital signals (RTTY, PSK31, PSK63, ...) like CW-Skimmer but it is free. This does not use an IQ stream. RCKskimmer controls HDSDR with Omni-Rig. HDSDR is set to SSB and demodulated audio sent to the program " Output Channel Mode for RX" to "AF" (Usually "AF to both Channels".)
Other programs that expect audio signals will usually be setup in a similar way.  Most digital modes expect USB audio.
Other CAT programs may control HDSDR if they can use the Kenwood protocol. WSPR, for example, incorporates HamLib CAT and may control HDSDR. WSPR-X does not have an IQ mode, an example of it's setup is on my main HDSDR page. 



CWSKIMMER
I show the use of a Softrock-type (basically any soundcard receiver that HDSDR can control, including the FCD, Peaberry..) SDR receiver with HDSDR and CW Skimmer to  search and pounce with a conventional  transceiver. But note, any SDR which HDSDR can control may be used with this same technique. You may use the transceiver audio, just using Skimmer to find the signal. Or the Skimmer audio can be used as shown below.

A simple way of using CW Skimmer with a Softrock would be to use it stand-alone in this way 192KHz can be seen with a suitable soundcard. 
HDSDR will add much more including interfacing with other radios. Unfortunately only 48KHz may be seen this way. 
October 2014 Note this new frequency changing utility http://dickwilliams.byethost17.com/SkimScanSR.html use a Softrock at 192ksps with Skimmer as an all-band reverse beacon. But not with HDSDR.








        

HDSDR emulates Kenwood's CAT protocol so Omni-Rig is set to "Kenwood". CAT communication can be established between HDSDR and any digimode program that uses Omni-Rig.
Skimmer Settings:- Note CW Pitch and Audio IF, this will enable tuning compatibility with a conventional transceiver used with CAT. This offset should be the same as that of the transceiver and HDSDR. I have set my FT847 to 800Hz. Omni-Rig http://www.dxatlas.com/OmniRig/
"Poll int" may be set to 100mS for quicker response.

Note that when in "Softrock IF" mode CW Skimmer defaults to 48KHz sampling. It is only possible to see 24 KHz bandwidth.
For 192KHz bandwidth "Softrock" mode may be used but HDSDR and CW Skimmer can not be connected by CAT. Both require tuning independently.
Alex says "This is by design and cannot be changed."


  Select the SDR input to HDSDR. Virtual Audio Cable http://software.muzychenko.net/eng/vac.htm Do not attempt to use the demo version for any transmit purposes!  This is used to send an IQ stream to CWSkimmer from HDSDR. HDSDR and CAT by OmniRig is used to tune the Softrock receiver and to also tune the transceiver to a selected frequency.
A new alternative to VAC is VBAudio here http://vb-audio.pagesperso-orange.fr/Cable/index.htm A single cable is free, a donation will get you more.

 


 
Note that the output
 sample rate can vary
 from mode to mode.
 Set it on the mode
 you will be using (CW)
 48000 will give an IQ
 bandwidth of about 
24KHz to be viewed 
in CW Skimmer.
         The IF offset is used to keep the IQ stream sent to CW Skimmer away from the centre, LO frequency. When HDSDR and CW Skimmer is used at 96KHz then an IF offset of 24KHz will allow CW Skimmer to see almost 48KHz of bandwidth with any spurious signals around the centre of HDSDR just at the edge of CW Skimmer's range. Set the frequency, press "C" on the keyboard.

Selecting "Tune fixed to 'LO<->Tune Offset" (just below the "set LO <-> Tune offset".) will fix the IF at the preset offset every time HDSDR is tuned. This setting is intended for other digimode programs that require their input to be on a fixed frequency. 





 
     
Choose the IQ output option. HDSDR output and Skimmer input must be the same so use I(Left)/Q(right)  if Skimmer is set Left/Right =I/Q . The IQ correction, if needed is set in HDSDR's Swap I and Q setting. If you also use Skimmer directly with a Softrock then it may well be already set to Right/Left =Q/I


























   
  this will be seen by calling Omni-Rig either from HDSDR or CW Skimmer. Note the COM port numbers must match your Virtual Serial Port setup. One free version http://sourceforge.net/projects/com0com/files/com0com/ another free to radio amateurs is  http://k5fr.com/ddutilwiki/index.php?title=VSP_Manager .






With these settings HDSDR and CW Skimmer tune together. 

But best use CW mode with the Output Bandwidth set to 48 or 96KHz as required. In this setup the actual mode is not important unless your are using HDSDR to transmit. But HDSDR's CW mode so far only uses the Return key and is not really practical.

When using digital modes you may wish to use HDSDR in compact mode, this will reduce CPU load:- Options - Visualisation. De-selecting both the upper and lower display just leaves the controls, no spectrum or waterfalls.

  

 Here OmniRig is set to synchronise the tuning of a conventional transceiver. Note that I have made no reference to antenna switching.
If you are going to use an external transmitter it is vitally important that a suitable system is used to provide protection for your SDR.
Many transceivers have an external receive antenna socket. It may be possible to add one to a transceiver that has not got one. 
A relay that works off the PTT line might be constructed or purchased.

    





G4ZFQ April 2013
alan4alan at googlemail com
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