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Re: SINAD Vs. Noise Figure Testing



----- Original Message -----
From: "Stan W1LE" <stanw1le@verizon.net>
To: <AMSAT-BB@amsat.org>
Sent: Tuesday, December 09, 2008 9:03 PM
Subject: [amsat-bb] SINAD Vs. Noise Figure Testing

> Hello The Net:
>
> Upon the suggestion of Domenico, I8CVS, I conducted some tests to
> compare SINAD to Noise figure testing.
>
> Noise figure testing was performed using a HP8970B with 346 noise source
> on a ARR preamplifier,
> one of their switched units, model SP144VDG.
> Performance was optimized at  144 MHz.  for a noise figure of 0.9 dB and
> gain of 25 dB.
>
> The preamp was added before the IC-910H, which was set to 144.000 MHz in
> a SSB (USB) mode.
>
> SINAD , SIgnal + Noise + Audio Distortion testing allows a complete
> receiver to be tested
> from the RF input port, thru the IF's and demodulation to audio.
>
> For SSB mode testing I injected a low level RF carrier, (~ -120 dBm),
> no modulation, into the preamplifer with RX.
> I tuned the RX frequency to 1000 Hz less than was actually injected.
>
> example: for a RF of 144.000 MHz, I tuned the RX,  in a SSB (USB) mode,
> to 143.999 MHz.
> SINAD instruments use a 1000 Hz tone for further processing.
>
> Connecting the audio output to a SINAD meter, in my case a Helper
> Instruments, Inc. model Sinadder Linear 5,
> I was able to get a SINAD reading from the meter.
>
> While monitoring the SINAD meter, I tweaked the preamplifier tuning and
> could not improve the original SINAD measurement.
>
> Conclusion: If the noise figure is optimized, the SINAD measurement will
> also be optimized.
>
> An additional test was performed, adding a fixed 10 dB BNC attenuator
after
> the preamplifier and before the RX.   The SINAD measurement did not
change.
> This indicated that at least 10 dB of excess gain was present and can be
> eliminated.
> It is always best to minimize system gains to maximize the ability to
> handle strong signals
> and to reduce higher order intermodulation distortion.
> Minimize system interstage gains until the system SINAD sensitivity or
> the noise figure is slightly degraded.
>
> In this example, if I was able to reduce 10 dB of excess gain, this
> would result in lowering
> the 3rd order intermodulation distortion by 30 dB .   !!!
>
> I hope this helps folks to consider SINAD testing of their system, to
> verify performance.
>
> Stan, W1LE   FN41sr    Cape Cod

Hi Stan, W1LE

Tank you very much to share with us your very interesting report.
I have this letter copied in a file for record.

73" de

i8CVS Domenico


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