[Premium-Rx] Mini-circuit amps

[Karl-Arne Markström]

If the system would be used with very small or narrowband antennas, it might be justified to
put the attenuator after the amplifier in order to preserve the amplifier noise figure.

However, this would limit the system to c:a 78 - 80 dB IM3 dynamic range, regardless of
how high the IP3 of the receivers are.

There are always trade-offs between noise figure and intermodulation performance, and since antenna noise figures
seldom are below 20 or 30 dB for full-size antennas in temperate climates, 
it seems that it would be reasonable to optimize intermodulation.

73/

Karl-Arne
SM0AOM

----- Original Message ----- 
From: "Ben Dover" <quixote2 at ix.netcom.com>
To: <Ka9p at aol.com>; <premium-rx at ml.skirrow.org>
Sent: Sunday, November 13, 2005 10:24 AM
Subject: Re: [Premium-Rx] Mini-circuit amps


> Hello Scott.
> 
> In my multicoupler I got to near unity gain by putting an attenuator pad on
> the amplifier output, and did so for a very specific reason besides gain
> adjustment.
> 
> With the pad placed on the output, it acts as a matched load on the amp, just
> in case there's any instability from an unmatched load. That in itself will
> improve the overall noise figure preformance of the amp.
> 
> Most Minicircuits splitters are resistive / inductive hybrids and tend to
> serve the same function, but the pad looks like PURE resistance to the amp, in
> addition to providing isolation from the splitter's inductive component.
> 
> 
> As far as varying gain by varying supply voltage is concerned, I wouldn't try
> that approach. Gain migh vary SLIGHTLY, but the available amp headroom is
> going 
> to vary much more quickly.
> 
> 73's,
> 
> Tom, W9LBB
> 
> 
> PS- STILL very happy with the 8718 here! It's one hell of a receiver!
> 
> 
> At 09:42 PM 11/12/2005 EST, you wrote:
> >  Because it was all cheap :)
> > 
> >   I've considered an attenuator on the output of the amp, but was also
> >curious whether the gain might be usefully varied by reducing the supply
> >voltage, and what effect that might have on noise figure (which is OK at
> >less than 3db) or 3rd order IMD (which ain't very good already at about +14
> >db).
> > 
> > Thanks for any ideas.
> > 
> > Scott _______________________________________________  Premium-Rx Mailing
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> 
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