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What is the real Noise Figure of AIDC-3733????

• Subject: [amsat-bb] What is the real Noise Figure of AIDC-3733????
• From: "Pieter Ibelings" <rfspace@xxxxxxxxx>
• Date: Mon, 7 May 2001 18:26:44 -0400

```Ok guys,

I am a little confused here and maybe I am missing something. I have seen
reports of noise figure measurements on the transystems converter in the 1.2
dB range. I am a little troubled by these figures. I have not made the
measurements myself because I do not have the N connector adapter to do it
right. Here is why I am a little confused:

1. The spec seems to indicate that this converter receives from 2150 to 2686
MHz so let's assume that the filtering inside is "Low Loss" at all of these
frequencies.
2. The LO in a standard unit is 2278.

When receiving 123 MHz at the IF (2401 RF), the image is at (2278-123=2155
MHz). From the converter specs this frequency is in the passband. We can
therefore assume that when receiving on 123 MHz, all of the noise power
present at 2155 will also be converted to 123 with little loss. This will
result in a doubing of the noise floor at 123 MHz. The noise figure might be
low in the preamp but since the image is also being converted, the resulting
conversion NF will be around 3 dB worse. This makes it impossible to have an
effective NF of 1.2 dB since subtracting 3 dB from this figure would result
in -2.2dB NF if an image filter is used. Since the desired signal (at 2401)
is only contained in ONE sideband and the DUT is converting BOTH sidebands,
shouldn't the NF be 4.2 instead? The 3 dB increase assumes equal conversion
gain and bandwidth for both sidebands.

Now the interesting part is:
If we change the LO to 2256 and increase the IF to 145 MHz, the Image moves
to (2256-145=2111 MHz). Based on the sticker on the case of the unit, this
frequency is not supported. We can assume that the filter is lossy and we
should get up to 3 dB better noise figure out of the converter.

Does all of this make sense? Maybe my brain is shot after being up all night
and all weekend (like the bats) listening to ao-40.

Check out page 20 of this PDF:
http://www.stanford.edu/class/ee314/Handout/HO11.pdf

Pieter N4IP

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