[R-390] DSP IF
Cecil Acuff
chacuff at cableone.net
Fri Apr 22 09:49:09 EDT 2005
That's what I had in mind too Bob...something like my old Kiwa MAP with IF
level notch, a dozen selectable filters, AM and Product detection...maybe
even Synchro and top it off with a very clean 5 watt amp with a well matched
speaker/cabinet arrangement. Been plenty of MAP's used with R-390A's and
SP-600's in the past...heck maybe still today.(sold mine a few weeks ago to
buy an SE-3...money went for car insurance and a HS class ring!) It allows
you to better use the radio on today's bands without having to touch a thing
in the radio...
I know there are those who will say "why not just buy you a new radio" Well
I did...and I like it a lot.(Icom 756 Pro II...all DSP) It only highlights
some of the deficiencies of the R-390A and SP-600 that could be solved with
an outboard IF/Detector/AF strip. Look at the archives....they're filled
with the groups quest for 1) improved audio... 2) fixes to improve SSB
functionality.... 3) questions about "what are we going to do with these
aging mechanical filters." We all love the front end and the tuning
arrangement...that is what makes the R-390 series what it is... We have a
love/hate relationship with the mechanical filter arrangement and would like
to improve the audio for broadcast listening. Seems to me what we are
talking about is the perfect solution if it is done properly. Personally I
am not a proponent of sound cards and PC processing. I know it's cost
effective because we already own it...but I like to use my PC for other
things while listening....
I'm like Bob...I much prefer to operate a boatanchor radio because of the
human interface but would like some ot the technology found in the new
stuff...I said some...not all! To be fair what is it we usually hate about
the sand state radio's...besides the cramped user interface....Phase noise,
display noise, poorly designed power supplies, poor audio.....just to name a
few. Some of that has gotten better in the new radio's but I still prefer
the tube stuff.
One suggestion from the past was to purchase a used Ten-Tec RX-320 black box
receiver used and put it to work as an IF/Detector/Processor. Feed the
audio out to a nice external speaker or even better to a Hi-Fi system... It
would probably work OK but I know it's not optimized for what we want to do.
Plus if you are going to do this from the ground up it should be implemented
in the 32 bit chipset as opposed to the 16. The 16 works good but I'm not
sure how much longer it will be around knowing how computer technology
changes. Again the RX-320 would require the use of the PC or a laptop to
drive it...I would much prefer knobs and buttons in a more portable system.
Anyway before you send the sheriff out to arrest the infidel keep in mind
this is just brain storming about a modern way to do what we have been
discussing for years in bits and pieces.
Cecil....
----- Original Message -----
From: "Bob Camp" <ham at cq.nu>
To: "Cecil Acuff" <chacuff at cableone.net>; "Bill Levy" <levyfiles at att.net>
Cc: "Michael Murphy" <mjmurphy45 at comcast.net>; "R390 LIst"
<r-390 at mailman.qth.net>
Sent: Friday, April 22, 2005 7:17 AM
Subject: Re: [R-390] DSP IF
> Hi
>
> Here's what makes this approach different than a off the shelf DSP radio:
>
> 1) The R390 has a *very* different approach to RF processing than what you
> can buy off the shelf today. They just can't afford to make them this well
> anymore.
>
> 2) Unless you have *very* small hands and fingers modern radios are a bit
> much to operate. Say what you will about R390 wrist it's a minor issue
> compared to the eight zilion buttons syndrome on a modern radio.
>
> 3) To make a processor work right you need to drive the AGC line on the
> 390 correctly. Putting a dsp radio on the 455 KC output does not allow you
> to do the AGC thing.
>
> 4) The hidden agenda here is to do a *very* good job on AM processing. I
> have yet to see a dsp radio that does even a so so job on AM. It would be
> nice to do it right.
>
> I can see good reason to start out with a PC program just to see what
> works and what does not work. In the end though I'd like to have something
> like my Sherwood box that sits in the rack with the R390 and spits out
> audio.
>
> Enjoy!
>
> Bob Camp
> KB8TQ
>
>
>
> On Apr 21, 2005, at 11:18 PM, Bill Levy wrote:
>
>> 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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>>>> >
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>>>
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