Delayed VOX

Just as with a normal transceiver the received audio has to be muted while transmitting.

The main difference is the 400msec +/-50msec latency in the audio. Incidentally it can go up for a short period of time.

In most cases your own voice can be heard via the websdr. Muting audio while transmitting is then necessary, because it disturbs talking.

Software VOX

The general idea is that if we talk (or give Morse), we don't want to hear ourselves back in the WebSDR. So we need to look for a way of muting the WebSDR while we transmit. You can do that in hardware or in software. For hardware see CW. For software solutions many ways lead to Rome, but wat we have running is the following implementation.

- a little VB (Visual Basic) program in the PC you are listening to the WebSDR is looking at the communication between CATSynch and the FT-950. For this to work you need a program like VSPE to split the COM port you use for the CAT communication between FT-950 and CATSynch. In this stream several interesting strings will pass and can be picked from the stream. For example a transmit string (TX) and the current Frequency Fxxxx. The TX string is used to mute the CATSynch application. For this we use a little freeware software app called NIRCMD. from the VB program the NIRCMD exe is called with the parameter 'mute CATSynch'. This works fast and reliable. If you stop transmitting, you call the NIRCMD program again with the parameter 'unmute'. To make sure you don't hear the last 400ms of your own transmission, the unmuting should be done with a delay of this 400ms.

This is not 100% reliable because the latency of the WebSDR is not 100% constant. But it works OK and you can fine tune the delay in the software easily.

If you are interested in the details of this software solution, you can contact the web operators for help.


PTT line

If using semi break-in the PTT line can directly be used to mute the audio. The delay has to be set to the maximum delay in the websdr e.g. 450msec. Also the normal VOX.

Hardware VOX

See CW