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Re: [Discuss-gnuradio] SDR 1000 progress

From: John R. Ackermann N8UR
Subject: Re: [Discuss-gnuradio] SDR 1000 progress
Date: Thu, 08 May 2003 12:16:43 -0400

Hi Brian --

Thanks for that info. I've used the PT5101 several times without any problems, but admittedly not in a low-level analog system. It is a complete switcher in a rectangular package about the size of an ordinary heatsink. It's definitely pricey, but if the noise isn't too bad, it makes a nice solution (FWIW, I've used an LM-2577ADJ DC-DC regulator to generate 20 volts from 12 volts for the LO brick in my 10GHz transverter, and with a bit of inductive filtering the switching sidebands are better than -50dBC).

I don't know if it'll happen before Hamvention, but I'll install a PT5101 and look at the output signal with my spectrum analzyer to see if it has any negative effects. I'll report back here.


--On Thursday, May 08, 2003 8:20 AM -0700 Brian Whitaker <address@hidden> wrote:


I haven't looked at the datasheet for that regulator, but anything that
spec's and efficiency is a DC-DC switcher (apposed to a linear
regulator). A drop-in replacement module is a neat idea, really, but it's
expensive because it's got a controller, a fair sized inductor, one or
two big FETs, and maybe even some capacitors (depending on how they
designed this).

The trade-off here will be output ripple on the supply line -- but again,
depending on the contol scheme, this might be localized to one particular
frequency... you just want to be sure that those spurious don't couple
into the signal path so much as to degrade your BER.

I'd be happy to chat with you about this... and help you design in a
better DC-DC switcher if need be.

Brian Whitaker
(applications engineer at Maxim)

----- Original Message -----
From: "John R. Ackermann N8UR" <address@hidden>
To: "Matthew Ettus" <address@hidden>; <address@hidden>
Sent: Thursday, May 08, 2003 5:27 AM
Subject: Re: [Discuss-gnuradio] SDR 1000 progress

--On Wednesday, May 07, 2003 10:40 PM -0700 Matthew Ettus
<address@hidden> wrote:

> I've been making progress will AC5OG's SDR-1000 radio.  See the update
>      http://comsec.com/wiki?SdR1000
> There is also the beginnings of a python program to control the rig
> with a nice GUI.  If anyone is experienced with GTK, python, and/or
> glade, your help with that would be appreciated.  Let me know if you
> are interested in helping out.

Great work, Matt.  I've had my radio for a few days now and have mainly
been wrestling with the Windows setup to get familiar with it.

Unfortunately, I don't have the programming skills you're looking for,
but I'll certainly be ready to test the code and provide helpful

I do have one hardware suggestion for anyone who's interested:  the 7805
regulator on the PIO board (the one with the big heatsink) is dissipating
*lot* of power and on my unit, the heatsink is burningly hot.  I haven't
made this swap yet, but the PowerTrends (now Texas Instruments, I think)
PT5101 regulator is a near drop-in replacement and offers 90%+
efficiency. I'm going to try plugging one into my unit as soon as I get
a chance.  It should reduce the overall current drain significantly, and
allow a much smaller and cooler heatsink on the PIO board.  The downside
is that it's a much more expensive part than a 7805 ($11.58 quantity one
from Digi-Key).

Oh, one question, Matt -- on the wiki you note to use the LINE OUT rather
than SPEAKER OUT on the soundcard.  All of the cards in my collection
have only a single output, usually labeled as SPEAKER OUT.  What to do
in that circumstance?  (And a follow-on question -- what about laptops
like my current work machine, a Dell Latitude C640 that has only two
sound card I/Os -- mic/line in, and headphones out?)


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