[Premium-Rx] Mini-circuit amps

[James C. Garland]

Scott,
I'm not sure your multicoupler-on-the-cheap will yield very good 
performance, but I'd recommend attenuating the input, rather than the 
output. You'll have a wider dynamic range on the amplifier by 
attenuating the input signal, which is probably more important than 
preserving the noise figure. Actually, with a 12 way splitter, you'll 
probably need all 20 db gain and then some. I'd guess you'll lose 
about 3dB for each port on the splitter.

You can't adjust the gain by fiddling with the voltage for the m 
onolithic minicircuit amps (I'm not sure whether yours is that type, 
however.)  In all the ones I've seen, the power supply voltage is in 
series with an external resistor that sets the bias current for the 
amplifier. The amplifier performance deteriorates rapidly if you move 
away from the optimal bias point.

Regards,

Jim

At 09:42 PM 11/12/2005, you wrote:
>I'm getting ready to fiddle with a MIni-Circuits ZFL-500LN amp ahead 
>of a 12 way splitter to use as a poor man's multicoupler.  Because 
>it was all cheap :)
>
>The amp has nominally 20 - 25 db gain or so, which I'd like to 
>reduce to make the system a unity gain set up.  Can anyone hazard a 
>guess what the best approach to doing this might be?  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
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