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R: R: 2.4 GHZ Down Converter Noise VS IF Gain??



Hi Dave NR1DX,

Since your TS-790A has not the provision to adjust the RF gain and to switch
the AGC OFF you cannot measure the increase of noise powering up your
converter ON because the AGC circuit tends to keep the audio level constant
changing the RF level input.

Unfortunately many modern VHF receivers or tranceivers do not allow to
switch the AGC OFF

For this reason i send  my AO40 144 MHz IF to a second converter
144 / 28  MHz  connected to an old HF Drake R-4C receiver and i tune
the AO40 MB on 29.323 MHz

In addition to the many advantages for satellite work,like different IF
filters and passband tuning,the HF Drake R-4C receiver like any other good
HF receiver has the provision to adjust the RF gain and to switch the AGC
ON and OFF

This feature make possible to use an old HF receiver like a good instrument
for many interesting measurements,in other words a new life for the old
HF receiver.

For example i can play to add external fixed or switchable step attenuators
between the 144 MHz IF and the 28 MHz IF and made very interesting
evaluations on sun-noise measurements at 2400 MHz

In addition using a receiver instead of a transceiver i eliminated the
possibility to inadvertently burn out my AO40 converter

It should not very difficult to find an old 144/28 MHz converter in the junk
box and a  good HF receiver in the surplus market with the above
prerequisite tuning the 28-30 MHz band

I am very satisfied to evaluate and optimize the 2.4 GHz Down Converter
Noise VS IF Gain using the above setup both for measurements and
AO40 operation.

73" de i8CVS Domenico


----- Original Message -----
From: Dave <nr1dx@arrl.net>
To: i8cvs <domenico.i8cvs@tin.it>
Sent: Thursday, August 08, 2002 1:15 PM
Subject: Re: R: [amsat-bb] 2.4 GHZ Down Converter Noise VS IF Gain??


> Dom
>
> First thanks again for the QSO yesterday morning on AO40.
>
> A very interesting way to look at the the problem. Unfortunately on my
> Kenwood TS-790A there is no easy way to turn off the AGC and no way to
> adjust the RF Gain.
>
> Here is what I do get
>
> With the converter off the S meter reads S0
> With the converter on the S meter reads S8
> and the audio noise increases by 8.5 db
>
> If I swtich in the front-end attenuator on the TS-790 (approx 10-12db)
> With the converter off the S meter reads S0
> With the converter on the S meter reads S2
> and the audio noise increases by 14 db
>
> I'm sure the readings are affected by the AGC action of the receiver, I
> would guess that the second set of readings are more indicative of overall
> system performance?
>
>
> Dave
> NR1DX
> nr1dx@arrl.net
>
> "A man who picks a cat up by the tail learns a lesson he can learn no
other
> way" .... Mark Twain
>












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