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[Discuss-gnuradio] AD/DA boards and RF front ends

From: Joshua Lackey
Subject: [Discuss-gnuradio] AD/DA boards and RF front ends
Date: Fri, 18 Apr 2003 10:27:55 -0700
User-agent: Mutt/


I've been following Gnu Radio for some time now, since at least 0.3, and
I've been meaning to mention a few of the things I'm working on.

I recently finished alpha-quality Gnu Radio support for the Datel
PCI-417 AD/DA board.  It is missing multi-channel support as well as
digital-to-analog, but the hooks are all there and I'll add the support
eventually.  I'd actually prefer it if Eric placed the code in his tree,
but for now go ahead and email if you would like a copy of the code.

A few things about the PCI417 -- it's twice as fast as the MC4020 and
twice as expensive.  (40Msps at ~$2400.)  Which isn't a real good deal
seeing how the PCI bus can only deliver around 32Msps (12 bit samples
"packed" in 16 bit fields.)  Definitely a nice card, but not for the
"why do I need such expensive hardware?" crowd.

Some words about Gnu Radio RF front-ends.  I couldn't convince myself to
spend $500 on a tuner module when I've got like 10 sitting in my garage.
(Cable boxes, cable modems, old VCRs, TVs...)  The first VCR I took
apart had a tuner module with 8MHz of bandwidth centered at 4.5MHz.  The
only bad part about this tuner module was it's I2L bus.  (Rather than
I2C...)  It appears that an I2L bus is more difficult to use than an I2C
bus, so I kinda stopped there.  I can still use this tuner module, but
Gnu Radio can only control where in the 8MHz bandwidth it is, I have to
change the channel on the VCR to move the 8MHz.  (The VCR also had a
power supply with 30V, 15V, 12V, 8V, and 5V pins.  How convenient!)

Moreover, just because this is a software radio project doesn't mean we
can't use hardware radios as our front end!  The problem is that the
MC4020 only pulls 20Msps and so cannot resolve the most common IF
frequency on these radios.  (10.7MHz in general.)  It should be possible
if you use two channels and get both the I & Q lines.

Given the ability to resolve a 10.7MHz IF, there are a few commercial
radios I know of which we would find useful.  The AOR AR-One,
AR-5000(+), AR-3000A(B), and the ICOM R8500, and R7100 all have a
10.7MHz IF with ~8MHz bandwidth.  (Note that Gnu Radio already has
support for the AR5000.)  The AOR AR3000 and the ICOM R7000 have the IF
and the bandwidth but they may not have an external IF jack -- these
radios thus require slight modification.  (YMMV.)

The above radios range from $5k to $1k new, so we're not talking loose
change here.  Another radio, not as nice as those above, is the ICOM
PCR1000.  It covers 100kHz through 1.3GHz and is only $260.  The PCR1000
doesn't have an IF jack on the back but I have located a 10.7MHz IF with
at least 5MHz of bandwidth inside the radio.  I'm in the process of
tapping that point (it needs amplification) and sending it to a jack I
drilled in the back.

Give me a couple of weeks and I'll release my Gnu Radio ICOM PCR1000
support.  (First I'm going through the schematics to see if I can't get
something slightly wider than 5MHz.)

I'd eventually like to have something similar to TalkPCR for Gnu Radio.
Except that the Gnu Radio version should have support for arbitrary
front-ends.  Cool huh?  Don't hold your breath, I've got a day job.

So, keep up the good work!  I'll contribute where/when I can.


Joshua Lackey, PhD. -- address@hidden

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