[R-390] DSP IF

[Bob Camp]

Hi

I would like to try something that retains the mechanical filters. One 
thing you could try is to do equalization in the DSP. That way you 
could take out the delay and amplitude ripple of the filters in *your* 
radio. You could also turn the 16 KC filter into something like an 18 
KHz filter (a modern upgrade).

As long as you are matching things up you can also calibrate the AGC 
voltage. More or less you build up a table of AGC versus db of 
attenuation. The R390 is amazingly linear in this respect so it should 
work pretty well. The net result is a "sort of" addition of more bits 
to your A/D converter. One of the reasons you need as much of this kind 
of thing as you can get is that A/D converters are relatively noisy 
gizmos. A 3 db noise figure converter is a tough part to find.

All of this would specifically match the DSP to the radio, but to me at 
least that's an advantage rather than a disadvantage. If you had some 
memory on the DSP you could store multiple radio profiles to match the 
various radios you used it with. The calibration and equalization stuff 
is pretty much transparent in normal use so you don't have a lot of 
added buttons or menus to cope with in normal operation. The gizmo 
needs to be pretty user friendly if it's going to be of any real use.

	Enjoy!

		Bob Camp
		KB8TQ



On Apr 22, 2005, at 11:44 AM, Tom Norris wrote:

> I have tried the IF out to my Pro II. Works well. Just put the
> 390/390A in 16KHz, erm, I mean 16 KC bandwidth and connect
> the IF out to the Pro/ProII/ProIII *receive input* (so you won't
> transmit into your 390!!) Works great! I have considered taking
> the output directly from the final mixer before it goes to the
> IF deck, but have been too lazy to try since it involves taking the
> top cover off, which I can't do since the radio is in a rack (an open
> air rack, in case someone fusses) and I am especially too lazy
> to pull the radio, and my back, just to get a few more KC of band
> width.
>
> Tom NU4G
>
>> Hi
>>
>> The idea of putting a DSP IF processor on the IF output of an R390 
>> sounds like an interesting project. The nice thing about the 390 is 
>> that you can get at both the IF output *and* the AGC chain without 
>> modifying the radio at all. Given the high performance RF section and 
>> the mechanical filters the result should be very competitive.
>>
>> Of course this gets into the general direction of witchcraft and the 
>> like ....
>>
>> 	Enjoy!
>>
>> 		Bob Camp
>> 		KB8TQ
>