[R-390] Filters

[mlmccauley at att.net]

Gary,

This sounds like a very powerful solution.

Do you have any schematics and code that you could post as a starting point?

I understand that the demo board contains the core DSP circuitry. I'm 
referring to what was added to that, the downconverter and other 
ancillaries.

Mike, WB5MYY



> Gentlemen,
>
> I've taken a slightly different approach to DSP on the cheap with R-390A, WJs, and other gear.  I also convert the IF tap down to a relatively low frequency, but then I use an Analog Devices SHARC DSP board to digitize the signal and do the DSP.  When I taught EE I had my students do bandpass filtering (Z-transforms), FSK demods, CW adapters, and the like using these. My favorite final semester project was to assign the specs for the Dovetron MPC-1000 and have students do the dual superhet on the SHARC.  Synchronous AM is easy on the SHARC boards with their Harvard architecture.  The boards have the PC Win based development environment included (ASM and C) and have codecs on board. The free software library includes many useful signal processing functions and IQ processing is a natural.  The tight coupling of the clock oscillator, codec, and SHARC means low phase noise and high performance.  Some kits used to cost $100.  Some were more... A lot more.
>   But the more reasonable SHARC boards bolted into TecTec enclosures are powerful peripheral devices.  Don't get less than a 32 bit device for most applications and make sure it has hardware floating point unless you are an experienced binary fixed point coder.  www.analog.com
>
> Gary WA0SPM / AAR8GI
> Chief Electrical Engineer, Digital Globe Inc.
>
>
> ------------------------------
> On Sat, Feb 16, 2013 9:44 AM MST Bob Camp wrote:
>
>> Hi
>>
>> "Multirate Signal Processing for Communications Systems" by Fredric Harris is a pretty good DSP text for the more advanced stuff in this case. It's about $160 on Amazon. It gets pretty deep pretty fast.
>>
>> If you want to stay Collins centric - "Digital Signal Processing in Communications Systems" by Marvin Frerking is more radio-centric and the author is an old time Collins Radio guy. Truth in lending - we've also bought each other a number of beers …. The book is about $152 on Amazon. It's a much better introductory text.
>>
>> --------
>>
>> But yes, the connection between "can I do this" and "should I do this" is a bit weak.  Of course it somebody has the cash to fund the project. I've spent more than a little time digging into using an R-390 as a front end for a DSP radio. No matter which way I try it, there are a number of limitations.
>>
>> By far the most rational approach (= cheap) is to simply down covert the IF output and use a PC+sound card for the DSP. That lets you use pre-existing software for all the heavy lifting. Do an I/Q downconverter board for 455 KHz and match it up with a $100 to $200 USB "sound card". If you want to do it right, set up a D/A to drive the AGC input on the radio.
>>
>> Bob
>>
>>
>> On Feb 16, 2013, at 9:51 AM, "Charles P. Steinmetz" <charles_steinmetz at lavabit.com> wrote:
>>
>>> John wrote:
>>>
>>> Anyhow, you folks have my curiosity up about the software requirements to do a DSP filter suitable for Collins mechanical filter replacement.  Can some of you gurus point me to where the math algorithms are defined?  Gotta be on the web someplace
>>>
>>> For the software, start with Hayward, et al., Experimental Methods in RF Design and then move to dedicated DSP texts.
>>>
>>> The software isn't the problem -- processing horsepower is.  Digitizing and manipulating 455 kHz with sufficient bit depth is still close to cutting edge.  Most DSP radios use a final IF in the 12-20 kHz range, and even that is taxing to process in real time.  This is not a job you can do with microcontrollers.
>>>
>>> But my previous question still stands -- once you have developed the DSP capacity to do the filtering, why in the world would you convert back to analog and put it through the 390A IF?  It would be plain silly not to have the DSP also handle AGC, passband shift, notch filtering, noise blanking, all-mode detectors, and synchronous AM, at the least.
>>>
>>> Best regards,
>>>
>>> Charles
>>>
>>>