Re: [linrad] A simple front end

[David Garnier <dgarnier@xxxxxxxxx>]

Gents,

Yes, the AD797 part does appear to be a nice low noise part.
I spent 14 years in Ultrasound and the RF preamp part we
used in product was the CLC5509.  (It has warts but, they all
have when you look at them closely.)  ;-)

I found a audiophile's website that has some experiance with
the AD797 part and suggests some others.

http://www.euronet.nl/~mgw/diy/preamps/uk_gainpre_2.html

Note, there are much better low noise regulators available these
days than the 7815 or 7915 parts.  Given the low noise opamp
such as AD797 I would take a serious look at the new low voltage
dropouts regulators that are available today.

Nice discussion guys.  73's & gl

dave garnier - wb9own

W6WO wrote:

> Thanks Roger, nothing so valuable as practical advice HI.  I was
> pleased to find that there is a DIP version of the AD797 and from its
> specs it it truly a very fine component. As it is such a wideband
> device I would ask if there any merit in limiting the bandwidth into
> the sound card?
>
> >If you want only the lower 25 KHz then you don't need quadrature
> >detection and can
> >get that with just an ordinary soundblaster type card running at
> >44100 HZ sampling
> >rate.
> >
> >to play around just do this:
> >
> >Direct conversion:
> >
> >antenna to
> >
> >[RF amp if needed] to
> >
> >TUF-1 to
> >
> >single AD797 to sound card
> >
> >
> >or dual conversion like I did, but omitting the crystal filter to
> >start.  As you
> >know, if you omit the filter you will then have images to worry
> >about, twice the
> >noise, etc, but for quick and dirty it will work.  I know because I
> >played with it.
> >
> >Try:
> >
> >antenna to
> >
> >[RF amp if needed] to
> >
> >TUF-1 to
> >
> >simple single transistor or ERA or MAR 1st IF amp to
> >
> >second TUF-1 to
> >
> >AD797 or other baseband amp to
> >
> >soundcard.
> >
> >You can make it as simple as you want and add the extra pieces
> >later.  I had a lot of
> >fun doing this and seeing what the practical effects of adding /
> >changing filters
> >were, etc., as I am not an electronics person and so it was all 'new
> >territory' to
> >me.
> >
> >73,
> >
> >Roger
> >W3SZ
> >----- Original Message Follows -----
> >>  Thank you all for the suggestions regarding a simple front end. Many
> >>  of you are aiming much higher than I am. My operation is almost
> >>  exclusively in the low 25 kHz end of 20 meters so I am not seeking
> >>  wide bandwidths and given the inherent atmospheric noise I am not
> >>  seeking VHF noise performance.
> >
> >
> >73,
> >Roger Rehr
> >W3SZ
> >FN20ah
> >http://www.qsl.net/w3sz


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