[amsat-bb] Re: New Preamp

Edward Cole kl7uw at acsalaska.net
Wed Sep 19 23:44:18 PDT 2007


At 06:48 PM 9/19/2007, i8cvs wrote:
>----- Original Message -----
>From: "Gary Memory" <gmemory at tks-net.com>
>To: "'Edward Cole'" <kl7uw at acsalaska.net>; "'i8cvs'"
><domenico.i8cvs at tin.it>; "'Amsat-BB'" <amsat-bb at amsat.org>
>Sent: Wednesday, September 19, 2007 7:12 PM
>Subject: RE: [amsat-bb] Re: New Preamp
> >
> > Adding a preamp in my case is a total disaster.  I could probably put a
> > diode in my coax line and then charge batteries with the resulting DC.
> >
> > 73!
> >
> > Gary, N7BRJ/DA1BRJ
>
>Hi Gary, N7BRJ/DA1BRJ
>
>Your case is similar to my situation in the bay of Naples and our problem
>cannot be solved using commercially made GaAsFET preamplifiers because
>they have a very low 1 dB compression point and a very low IP3 intercept
>point.
>
>Buy the way very rapid advances have been made in the last twenty years
>in the development of semiconductors.It seemed that at first the field
>effect transistor (FET) and then GaAsFET were getting more and more popular
>over bipolar transistor, especially with respect to the noise figure from
>VHF to UHF
>
>However the modern bipolar transistor is still of importance in receive
>technology,especially since a well know type of "Noisless Feedback Circuit"
>developed by Dr. David Norton allow them to be made more linear and
>exhibits less noise than a FET and greater IP and dynamic range
>than a GaAsFET
>
>Since desensitization and overload are becoming a serious problem
>particularly in 2 meters as more and more amateurs started using high power
>linears and large directive antennas, the Norton circuit seems to be a
>modern solid state solution to the designe goals in those case like our case
>when, for 2 meters satellite communications, an extremely low noise figure
>less than 1.5 dB is not strictly necessary but, a very high IP and
>compression performance may be more useful.

Wonder what your opinion is of the mfg-1801 low-power transmitting GasFet?
This is what I am using for eme with fabulous results.

Although I stated earlier having no RF interference that is probably 
not completely accurate.
But it seems this preamp is very durable and not particularly 
susceptible to RF overload.  It was measured at 0.15 dB NF with 16.8 
dB gain at CSVHFS in 1999.

With four 10-element yagis I am talking with 2m mobile and even a 
couple HT's over 70-miles from me.  That is on FM simplex.


73,
Ed - KL7UW
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