More Re: [TenTec] Orion redefines the meaning of ... AGC OFF

[Carl Moreschi]

Ok, just a quick simple test with the K2.  Tuned to 28.6100 mhz with preamp
off, no difference in noise with antenna connected or not.  With preamp on,
there is a very noticeable increase in noise with antenna connected verses
not connected.  The S meter never moves during this test indicating AGC
action is not occurring.

Carl Moreschi N4PY
Franklinton, NC
----- Original Message -----
From: "Sinisa Hristov" <shristov at ptt.yu>
To: <tentec at contesting.com>
Sent: Sunday, February 08, 2004 3:07 PM
Subject: Re: More Re: [TenTec] Orion redefines the meaning of ... AGC OFF


> 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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