[hpsdr] hpsdr Digest, Vol 11, Issue 12

[Giancarlo Moda]

Hi Frank,

Edson gave us interesting info regarding his
simulations with J310 and BF245 JFETs.

We must try any solution to see if it performs better
than any other one ... simulation is OK and real life
is something else even for electronics circuits and
components.

The SD5000 could be an IC to try. The problems with
FETs are two, mainly, the high Ron and also the very
high gate drive to have them switching. The FST serial
of switching permit the H-Mode Mixer to be easily
reproduced (no adjustments) and due to their low Ron
and TTL type of gates switching it gave a very hot
front end ... low insertion losses (less tha 5dB), NF
around 5dB and very good IP3 around +40dBm (to +45dBm)
and with no diplexer termination or driving a roofing
filter with an IP3 of at least +35dBm. New video
switches may improve on these figures ... need to be
tested.

A trial with JFET (but none has the same
characteristcs) or better SD5000 (same chip) would
permit to see if the QSD switching noise is lowered or
nulled or it is similar to the one measured with FST.

In a few words we do need to TRY, TRY, TRY, TRY
....and share results if good or not good.

ECL logics are a very good technology but high current
and very low signal levels are probably generating
other problems. 

73

Gian
I7SWX


Message: 1
Date: Tue, 16 Jan 2007 07:02:35 -0800 (PST)
From: FRANCIS CARCIA <carcia at sbcglobal.net>
Subject: Re: [hpsdr] hpsdr Digest, Vol 11, Issue 12
To: hpsdr at hpsdr.org
Message-ID:
<590861.23255.qm at web82307.mail.mud.yahoo.com>
Content-Type: text/plain; charset="iso-8859-1"

Hi All,
  ECL is pretty easy to use. All you need to do is
treat it like an RF 
device. Then just follow the loading and transmission
rules. When AC 
logic came out I saw all the old ECL rules surface. 
  I wonder why nobody has thought of using FETs as
switches? The first 
H mode used an SD5000. Why not look at discrete parts.
I have found 
stuffing too much stuff on one substrate can cause
cross talk. I was 
actually surprised with the performance of the FST3253
at HF. This may take 
a second transformer but if it was rated for 50 or so
watts it should 
work. 
  I have a hard time trusting the HP8640B for dynamic
ranges over 100 
dB. I get the feeling theer is interaction between
generators. A friend 
who has been doing high dynamic range stuff uses a
pair of isolation 
amplifiers after the generators to avoid problems.
  lurker frank wa1gfz. 
  




 
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