DES with Saber - little problem...

[radio-link]

Hi,

I am using two Motorola Saber III radios with DES, and they show the effect that the receiving radio does not sync when the transmitting radio starts in secure mode with immediate very loud noise, like background noise from wind or from an engine. It can be provoked when you blow into the mic and press the PTT. Sync only occurs when the noise stops. Then the sync is kept, even when the same nois is applied again it is just transmitted as it should.

The radios work in 20 KHz bandwidth mode / 4 KHz deviation, alignment is just perfect ( I checked it), deviation in clear and secure is just right, and the eye diagram of the 12kbps FSK looks good and is as expected. The DES hybrids are NTN4714 and NTN5835, the radios are German Public Safety version (MX3013 / Z42QXK7139AN). XL is deactivated due to worse audio quality.

Is this effect known?

[radio-link]

Update: When I disable the key recognition the effect is gone. So it seems the algorhithm fur detecting the correct key is buggy?! Never had this with Systems Sabers or XTS5000, but I must admit, the Sabers are quite old As I can live with the noise from wrong keys the problem is solved now.

[radio-link]

Second update: For those who are interested, this document shows the background and the reason why I have experienced this:

http://dk5ras.dyndns.org/tmp/FED-STD-1023.pdf - see 3.3.3. The document is about INDICTOR and WINDSTER encryption, but the underlying CVSD is the same with DES.

Key recognition is done with alternatin zero/one patterns, when silence is transmitted. It seems that older radios do not transmit a "preamble" of silence, so when there is no silence no valid key is recognized.