[R-390] DSP IF

Thu Apr 21 23:18:36 EDT 2005

Golly Cecil and Mike
What a can of worms you have opened up.
Why not just buy a DSP radio and tune it to 455 and plug that into the 390a.
Wouldn't that accomplish the same darn thing.

Now no one say why go to the expense of another radio......thats what we do 
fellows. Any excuse to try something requires a new radio!

N2WL

----- Original Message ----- 
From: "Michael Murphy" <mjmurphy45 at comcast.net>
To: "Cecil Acuff" <chacuff at cableone.net>; "Bob Camp" <ham at cq.nu>; "Dave 
Maples" <dsmaples at comcast.net>
Cc: "R-390 HF Receiver List" <r-390 at mailman.qth.net>
Sent: Thursday, April 21, 2005 10:26 PM
Subject: Re: [R-390] DSP IF

> Cecil,
>
> We built something like this at work (at a higher IF frequency 45 MHz!!).
> I'm no expert but..
>
> I think you have to sample the IF with an outboard A/D converter first
> before sending it into the DSP to keep the costs down. If you want to talk
> about a digital IF processor in an outboard box, the intermediate 
> frequency
> spectrum (of the R390A) is first digitized by an analog-to-digital 
> converter
> (ADC) into a slower digital data stream; this contains all of the signals
> present in the IF. Nyquist says we need to sample at twice the frequency 
> of
> our 455 kHz IF and most converters can easily do this. Even low cost Sigma
> Delta converters (like the one in your sound card) get close to being able
> to do this. There may be some Sigma Deltas around which can do 1 MSPS or
> better.
>
> The digitized IF signals are then translated to baseband by something 
> called
> a Digital Drop Receiver or Digital Drop Converter  (DDC). This could be a
> chip or it more likely is code running in an FPGA or DSP core.
> Downconversion is accomplished by digitally mixing the intermediate 
> spectrum
> of frequencies with a sinusoidal waveform generated by a synthesizer. The
> baseband output can be thought of as the R390A receiver's 4th IF, which is
> selected from the DDC's other output frequencies by a very efficient
> brick-wall digital filter. It is at this stage that the outboard circuit 
> can
> crank in some serious selectivity. Remember, we are talking about
> programmable gate arrays or pure software in a DSP for all of these stages
> and functions.
>
> The DDC's baseband output is fed to a DSP (or into another section of the
> DSP or FPGA which is actually acting as a DSP), which performs signal
> demodulation. The DSP's output is then converted from the digital domain
> back into the analog domain by a digital-to-analog converter, amplified, 
> and
> is made available to Cecil via a bigass tube amplifier and a speaker.
>
> Mike Murphy   WB2UID
>
>
> ----- Original Message ----- 
> From: "Cecil Acuff" <chacuff at cableone.net>
> To: "Bob Camp" <ham at cq.nu>; "Dave Maples" <dsmaples at comcast.net>
> Cc: "R-390 HF Receiver List" <r-390 at mailman.qth.net>
> Sent: Thursday, April 21, 2005 8:15 PM
> Subject: Re: [R-390] DSP IF
>
>
>> The thoughts of an  455 Khz IF based DSP filter system has been rolling
>> around in the back of my head for quite some time.  An outboard accy. of
>> that type would be very popular considering the number of radios that use
>> the 455 Khz IF.  I might try sending the IF output from my R-390A to the
>> antenna port on my Icom 756 Pro II and use the Pro as an
> IF/Processor/Demod
>> and see how things stack up...
>>
>> My understanding is that DSP processors that go up to 455 Khz are quite
>> expensive and mostly smoke and mirrors at this point.  You'd have to down
>> convert to something lower....
>>
>> Cecil...
>> ----- Original Message ----- 
>> From: "Bob Camp" <ham at cq.nu>
>> To: "Dave Maples" <dsmaples at comcast.net>
>> Cc: "R-390 HF Receiver List" <r-390 at mailman.qth.net>
>> Sent: Thursday, April 21, 2005 6:32 PM
>> Subject: [R-390] DSP IF
>>
>>
>> > 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
>> >
>> >
>> >
>> > On Apr 21, 2005, at 5:22 PM, Dave Maples wrote:
>> >
>> >> All: Hmmm...why stop there?  Get a large touch-screen display so the
>> >> radio
>> >> can REALLY be "man-sized", and follow this with a hue-changing routine
>> >> where
>> >> the panel, knobs, and display fade from color to color.
>> >>
>> >> Add DSP to correct distortion in the audio chain.
>> >>
>> >> Possibilities are endless...
>> >>
>> >> Dave WB4FUR
>> >>
>> >> -----Original Message-----
>> >> From: r-390-bounces at mailman.qth.net
>> >> [mailto:r-390-bounces at mailman.qth.net]On Behalf Of Barry
>> >> Sent: Wednesday, April 20, 2005 5:49 PM
>> >> To: r-390 at mailman.qth.net
>> >> Subject: Re: [R-390] Crayola front panels
>> >>
>> >>
>> >> Don't paint the front panel at all.  Mount motor drives on all front
>> >> panel
>> >> controls with the appropriate serial/parallel interface to a computer
>> >> program that looks like the front panel.  Put the R390x right up next
> to
>> >> the
>> >> antenna to eliminate any feedline loss.  Run the controlling wires 
>> >> from
>> >> there to the computer.
>> >>
>> >> Change the color any way you want, any time you want.
>> >>
>> >> Barry(III) - N4BUQ
>> >>
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