[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

[linrad] Homebrew I/Q chains and Op-amps, compiling Linrad

Hi, Zaba, and all,

I am glad to see that you are making progress! Building small receivers is fun!

I wish I could help you with the hash table stuff, but I have no idea what the problem is. I have only the most basic idea of what a hash table is or does. For those like me who have only a vague idea of what a hash table is, here is an interesting reference. It won't help your problem though, as its way to basic and general.


Since you mentioned possible op amps to use for the final stage of your receiver I have a question for you and the group.

Around 2000 or so when I built my simple EME receiver to use with Linrad, it looked like the AD797s had the best noise specs and so this is what I used.

Now it seems that some of the cognoscenti tout the LT1128A and don't even mention the AD797.

The typical noise at 1 kHz for the AD797 is 0.9 nV/sqrt[Hz] and that for the LT1128 is 0.85, and max figures are 1.2 for the AD797 and 1.1 for the LT1128, so the LT1128 is ever so slightly better in this respect.

The gain bandwidth of the AD797 is 110 MHz and that of the LT1128 is 20 I think; I guess that doesn't matter for our baseband amps.

The slew rate of the AD797 is 20 V/usec and of the LT1128 is 5V/usec.

So my question is:

For use as the 'last stage' of amplification before the soundcard for a system sampling at up to 192 kHz, are these two chips pretty much equivalent given the [to me] tiny differences in noise, or is the LT1128 clearly superior, and if so, why. If the LT1128 would have advantanges under some conditions, for some projects, what would those conditions or projects be?

If there is not a big difference in performance for this purpose, why is the LT1128 currently the 'ultra low noise op amp of choice'? I don't think it is cost, as from Digikey they both cost 8-9 USD in single quantities.

I apologize in advance if this is a stupid question. An electronics wizard I am certainly NOT. Hence the attempt to learn.

PS I got a really pleasant surprise yesterday when I tried to compile and run Linrad 02.14 on an old P3 with a pre-Fedora version of Redhat Linux installed and everything compiled and ran perfectly, including XLinrad!!

Thanks and have a great day, all, and



On Tue, 06 Jun 2006 06:00:24 -0400, 'Zaba' OH1ZAA <zaba@xxxxxx> wrote:

Sir Roger & all!

Though I have the complete WSE-line here, I am still missing
the proper power supply (-15V/+15V) amperage to fire them up.

On the other side it is fun to build something small from time
to time, so I constructed the low noise I/Q-amplifier according
to SM5BSZ/Leif's Figure 2 in "Linux PC-radio. Optimised direct
conversion receiver for 144 MHz using standard Schottky diode
mixers" [http://www.sm5bsz.com/linuxdsp/hware/optiq.htm].

As it turned out the 2N2222A is an excellent choice for the
input-transistor. I had some 1980's stock, but ON Semiconductor
[http://www.onsemi.com/PowerSolutions/product.do?id=P2N2222A] is
listing this P2N2222A model with plots of noise figures below 1 dB
over a wide range of impedances and bias. I used the RC4136 for
the op-amps, but if you need to steer a Delta 44 to full range
with the 96 kHz setting, then  it may be better to take a NE5532
or a similar type for the output stages, with a higher slew-rate
than the RC4136.

Roger Rehr

This message is sent to you because you are subscribed to
 the mailing list <linrad@xxxxxxxxxxxxxxxxxxxxx>.
To unsubscribe, E-mail to: <linrad-off@xxxxxxxxxxxxxxxxxxxxx>
To switch to the DIGEST mode, E-mail to <linrad-digest@xxxxxxxxxxxxxxxxxxxxx>
To switch to the INDEX mode, E-mail to <linrad-index@xxxxxxxxxxxxxxxxxxxxx>
Send administrative queries to  <linrad-request@xxxxxxxxxxxxxxxxxxxxx>