Topband: New High-Performance Beverage Pre-amp

[K9AY]

> Is the IP3 spec referred to input or output?
> The 1 dB compression spec (+15 dBm) does not make sense in
> light of the 20 dB gain spec.  It implies that you can get
> +34 dBm out if you put +15 dBm in.  +34 dBm is 2.5 watts.
> Also, it would be useful to know the IP2 spec.
> Thanks,
>
> Rick N6RK

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I'm also interested in hearing about the input IP3 performance.

The new InGaP HBT MMICs are interesting because they can run more power and
have lower 1/f noise than earlier GaAs MESFET amps.

So far, I have not used these GaAs MMICs because they are still short of
discrete design performance. All devices I know of specify output IP3
performance, with input IP3 being lower by the amount of gain.  Thus, a +35
dBm IP3, 20 dB gain spec corresponds to an IIP3 of +15 dBm, which is not
bad, being about the same as a typical diode double-balanced mixer.
Similarly, the 1dB compression point will also be an output specification.

For comparison, the classic negative feedback 2N3866 circuit I use in my
preamps has around +30 dBm input IP3 with 60 mA bias.  Two of these amps in
push-pull, and biased a bit stiffer can deliver input IP3 exceeding +40 dBm.

73, Gary
K9AY