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R: TranSystem AIDC - Another noise story



Hi  Ward,

Excellent  job  because your measurement demostrate that the single sideband
noise figure decreases increasing the image rejection.
If no special selectivity is provided,the mixer will exibit a passband curve
both for the required and image frequency.
This means two equal powers are taken from the white noise spectrum and if
the image spectrum is not attenuated at all  (stub not retuned) the noise
figure is 3 dB "too good" and it is the double sideband noise figure that
has been measured,and not the single sideband measurement at the required
frequency.
My DB6NT homebuilt transverter has a 1,5 dB single sideband noise figure and
a 40 dB image rejection at 2112 MHz

Wath is the dB image rejection of your TranSystem now after stub retuned to
image frequency ?

73 de i8CVS Domenico


----- Original Message -----
From: wc0y <wc0y@email.msn.com>
To: <amsat-bb@AMSAT.Org>
Sent: Wednesday, May 23, 2001 3:45 AM
Subject: [amsat-bb] TranSystem AIDC - Another noise story


> Another email about TranSystem converter noise figure!
>
> I did take some more measurements and came up with a new modification
since
> this topic is of such interest.  Thanks go to Mark, N0NSV, for sending me
> his TranSystem converter to work with.  He will get it back working much
> better.
>
> I used a sensitivity measurement method with a signal source and spectrum
> analyzer with Noise Marker capability.  The advantage is that I did not
have
> to guess at how to account for the noise contribution from the image
> frequency... it is included in the measurement.  The HP8970A noise figure
> meter does not automatically account for the image contribution.
>
> The results, in a nutshell, are as follows:
>
> With no mods => 9.8 dB NF !!
> With stub removed => 4.1 dB NF (123 and 145 MHz IF)
> With stub retuned to image frequency => 1.8 dB NF
>
> I retuned the stub to notch the 2111 MHz image frequency by soldering a
> 0.5pf chip capacitor on the open end of the stub, shifting its frequency.
>
> Details can be found at http://communities.msn.com/wc0y
>
> 73,
> Ward - WC0Y
>
> ----
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