Carl Moreschi wrote:
> With the preamp on, the signal jumps up a lot in audio
> volume. This is a symptom of insufficient gain.
Increase in audio volume demonstrates only that
the preamp has some gain, with AGC threshold
not reached without preamp. Nothing more and nothing
less than that. Taken alone, this says nothing
about receiver quality, sufficiency of gain, etc.
Your test also compares signal to noise ratio with preamp off,
concluding that K2 produces bad S/N with preamp off.
This is a meaningful test comparing receivers'
noise figures with preamp off. Orion's active mixer
can reasonably be expected to have a better noise figure
than K2's passive mixer.
Can I recommend a more repeatable noise figure test,
which even doesn't require any signal on the band?
Please test for the difference in noise level
with antenna connected and disconnected
(Strictly speaking, antenna shall be replaced by a 50 Ohm termination).
Meaningful compare requires that AGC threshold is not exceeded.
Sufficiently low noise figure is indicated by a 10-12 dB
increase in audio noise with antenna connected.
Anything more than that is useless, while lower values indicate
that receiver's internal noise will mask some of the signal.
> K2 is much poorer voice quality than the Orion listening to SSB signals.
> This is because the K2 ssb filter is too narrow.
And probably not as flat as Orion's DSP filters.
In-band flatness is even more important for perceived
voice quality, than the bandwith alone.
> It is much easier to get good IP3 and BDR numbers if you design with a low
> overall gain factor.
It's also easier to get bad IP3 if one designs with high gain,
as many other designs prove :-)
73,
Sinisa YT1NT, VA3TTN
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