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Adding dual modulation to FM function to allow for CTCSS

By VK3NH •  2017-06-28 11:37:02 •  182 clicks
To the designers.

When testing conventional analogue receivers in amateur repeaters and in commercial use, it is often necessary have the capability to generate a CTCSS along with the test tone in order to test the receiver.

If all you can do is just generate the CTCSS tone, then all you can tell is that the receiver is working at a particular sensitivity and that the mute opens. It does not allow you to test if there is distortion in the receiver or repeater system overall.

I therefore suggest that software be modified to provide an additional option allowing simultaneous generation of a CTCSS tone. The simplest way to implement this would be to set the tone frequency manually but you could use a lookup table. I suggest that the deviation level for the tone (if enabled) should be 20% of that set for the main test tone.

I base this on the relationship of the tone, to test signal deviation given in an article at http://urgentcomm.com/mobile-voice-news/ctcss-z

For 25kHz channels test tone is 3KHz FM deviation and CTCSS tone FM deviation is 0.7kHz. For 12.5kHz channels test tone is 1.5KHz FM deviation and CTCSS tone FM deviation is 0.3kHz. i.e. approx 20%

Having the dual modulation tone capability would greatly increase the KC901Vs value in both amateur and commercial use especially when used in conjunction with a scanning receiver or SDR to analyse the repeaters output.

regards Noel
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