[App_rpt-users] audio for direct VCO FM

[Jon Rorke]

If you are talking about connecting a fob/URI directly to a modulator 
input of a direct FM radio, then you can set up USBradio or maybe 
simpleusb, to set txprelim=yes then it will preemphasize and limit the 
audio.

Not sure where your 12 KHz limitation is reference to but if you are 
looking to limit at 25 Khz(5KHz), then set TX audio with a 1K tone @ 3K 
deviation. If you intend to limit at 12.5 KHz(2.5KHz), then set 
deviation with a 1K tone with 1.5 KHz deviation.


I have several radios I feed into direct mod with voice and tone.

Jon VA3RQ

On 5/31/2016 3:40 AM, Steve Wright wrote:
> Gurus,
>
> What are the limitations with audio-driving a 50MHz FM Transmit VCO 
> directly?
>
> Sorry that's a really open-ended question.  I suppose it will vary per 
> each chan_ driver as well, as well as the emphasis settings and so on.
>
> So dealing with the issues of emphasis, compression, (audio)bandwidth 
> limiting and so on - how much can be taken out of the radio and 
> handled by the chan_ drivers, and how different are they each?
>
> It was suggested elsewhere, that everything over 12KHz be not 
> permitted anywhere near an FM modulator stage, but how much does that 
> actually happen with the CM119 chipset?
>
> I ask because on a transmit-only site, there hardly seems to be any 
> point to having a "transceiver" there at all, when a clock generator, 
> buffer, PA, and filtering, is a fairly simple unit.
>
>
> Cheers,
> Steve
>
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