Recording IQ - how to start and stop as there is not wav menu anymore

[Raj, N2RD]

Hello,

 I am trying to set up a 'timemachine' to record IQ off the air and play back, primarily to demonstrate receivers.  The old Thetis has a WAV menu and current one does not.  I looked at /Setup/Audio/Recording.  I cannot find a button for it?  Do I have to bind a key? What is a preferred one?

Thanks for tips and pointers,

Raj, N2RD

[Robert Muir]

Interested in this also, if you find a solution please share. sorry no help Bob ei3grb

[Jim Basu]

Could this work?

https://github.com/n9bc/thetis-on-the-web/tree/main

[do1kl...@gmail.com]

maybe this one could help?

https://youtu.be/LQlAEiWw3h4?si=IoycgbqtavoZuVmI&t=682

[Robert Muir]

On Monday, May 18, 2026 at 5:05:36 PM UTC+1 do1kl...@gmail.com wrote:

maybe this one could help?

https://youtu.be/LQlAEiWw3h4?si=IoycgbqtavoZuVmI&t=682

Brilliant, Thanks de ei3grb 

[Rajiv Dewan]

The video you shared is very helpful if you want to record audio off the air or mic and then to play it back .  

I/Q recording and playback is a different matter altogether.

With quick record on Thetis and Quisk you can record I/Q and play it back, but only for the software on which it is recorded. When playing back through recorded iq spectrum is put into the receive buffer and you can re-receive it, tuning around the recorded spectrum on Thetis.  ***It does not put the IQ recording into the transmit buffer and hence you cannot transmit the IQ slice recorded.***  Quisk and other software that I tried, all the same limitation.  I think it is an architectural limitation of Hermes Lite.

You can always record the audio off the air and retransmit it back on the frequency you are on.  That is limited to the bandwidth of the demodulated audio.  It is not the whole receiver slice.

I have not been able to get the *I/Q* playback through the transmit buffer where it does not just transmit a single audio stream but the whole bandwidth (48KHz) captured.  

This is what I have been able to do using Hackrf Pro (Hackrf One is similar).  The I/Q recording can be sent to the transmit buffer and whole receiver slice recorded is recreated in rf.  I did this on the 40m band yesterday.  I recorded 4 minutes of 1.5MHz receiver slice centered around 7030 MHz. I played it back through the antenna port of the hackrf, and with an attenuated an coax into the antenna port of a QRP Labs QCX.   I could tune around on the QCX receiver and listen to different stations that had been recorded.  I had 1.5MHz bandwidth, more that what the 40m QCX can tune.

I/Q recording on the HackRF takes 16MB per second or about 1 GB per minute.  I recorded about 4 minutes worth.  The software allows the transmitter to play the file in a loop and so I can have a continuous spectrum to play with for however long I keep the hackrf transmitting.   I plan to to use it demonstrate different qrp receivers. They will all be fed the same rf spectrum using coax, attenuators and splitters.    Hackrf will not be transmitting  the recorded spectrum on the air.     

With hackrf and condaradio software on the PC, recording is done with hackrf_transfer -r and retransmit with hackrf_transfer -t functions.  (These are all python functions).

The Portpack is a handheld add on for the hackrf that makes it a device for easily recordinging and playing back of spectrum. It uses a sd card for storage and the files are limited to 4GB.  There are numerous videos on YouTube where people use it for nefarious purposes, or at least unlicensed purposes, by actually transmitting the recorded spectrum back upon the air. You can imagine the nefarious uses.  It will even do it for nfc transmitters/receivers.   

In my case, I do not have the portapack.  I use the PC as the recording / playback controller.  

Raj, N2RD

-- 
You received this message because you are subscribed to the Google Groups "Hermes-Lite" group.
To unsubscribe from this group and stop receiving emails from it, send an email to hermes-lite...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/hermes-lite/6b632eb7-b99e-4db6-8d2b-e10815032517n%40googlegroups.com.

[Jim Basu]

Perhaps the use of Virtual Audio Cables (for example, VB-Audio) (two of them: I and Q) and Audacity (free software) may be of help.

Under Thetis VAC, one has access to virtual audio cables

And Audacity can use Virtual audio cable channels

I asked AI "how to use audacity for IQ data"

It gave me step by step direction on how to do this (Record and Playback)

You may try similar ...

(option 1) Importing  IQ data
Most SDR software exports IQ data as 16-bit or 32-bit stereo WAV files.
Open the WAV file directly in Audacity.
The left channel typically represents I and the right Q.

(option 2) Recording IQ Data Directly

Select the Thetis virtual output (VAC1, then whatever chn) as the recording input device.
Set the sample rate to match your desired bandwidth (e.g., 96000 Hz for 96 kHz of spectrum).
Record and then Export as 16-bit PCM WAV

I haven't had a chance to try this, but it makes sense to me.

jim