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R: Orbit 250 apogee



Hi  John,

The metod that you suggest  is the metod  that i succesfully use from 1977
to accurately measure  the sun noise against the cold sky noise and
obviously now the AO40 transponder noise against the cold sky noise:

 STEPS:

1) Disable the AGC control
2) Switch  ON the product detector (CW or SSB) to get the receiver linear
3)Reduce the RF control to minimum
4)Increase the audio control  until you read the indication of your  AC
   voltmeter on the audio in order to get a  0 dB reference indication
   with the antenna aimed  to the cold sky and call  V2 this indication
5)See were the sun is in AZ/EL using  your tracking program
6)Put the antenna on the AZ/EL of the sun and read the increase of  voltage
   due to the sun noise and call V1 this indication

Compute the increase of sun noise in dB

  dB= 20 log    (V1/V2)
                    10

This metod is quite accurate and widely used by EME operators to check the
receiver performance but it is affected by the AC voltmeter non linearity
and AC fluctuations.
A better circuit  that i have recently built is a linear dB-meter wich uses
an AD636JD from Analog Device.
This chip is connected to the receiver audio output (headphone jack)
 A  0-100 microampere instrument connected to AD636JD is linerly calibrated
in dB from 0 to 20 dB or from 0 to 10 dB depending of our needs.
Using this circuit i can accurately measure  5 dB of sun noise increment at
2400 MHz  with a 1,2 meter dish
and 4 dB of sun noise increment on 10451 MHz using 60 cm dish

The schematic diagram  of the instrument has been published in Radio Rivista
2/96 page 26 .Radio Rivista is ISSN 0033-8036
Using this metod and this instrument in certain AO40 MAs i measure a strong
4 to 8 dB  transponder noise increment and fluctuation as soon the matrix
is switched  ON

73 de i8CVS Domenico

----- Original Message -----
From: John Stephensen, KD6OZH <kd6ozh@gte.net>
To: <topcat@mail1.stofanet.dk>; Jesse Morris <w4mvb@juno.com>
Cc: <amsat-bb@AMSAT.Org>
Sent: Saturday, May 19, 2001 2:27 AM
Subject: Re: [amsat-bb] Orbit 250 apogee


> The converters and preamps shouldn't add to the nonlinearity unless they
are
> overloading the receiver.
>
> However, many S-meters are not very accurate so, if the receiver AGC can
be
> disabled, connecting a VU meter or AC voltmenter to the audio output will
> provide more accurate results. However, there are several products on the
> market that don't have an AGC off switch so many are with S-meter
readings.
>
> If you want a receiver with an accurate S meter see QEX for May/June 2000
> QEX.
>
> 73,
>
> John
> KD6OZH
>
> ----- Original Message -----
> From: "Jesse Morris" <w4mvb@juno.com>
> To: <topcat@mail1.stofanet.dk>
> Cc: <amsat-bb@AMSAT.Org>
> Sent: Friday, 18 May 2001 01:09 UTC
> Subject: Re: [amsat-bb] Orbit 250 apogee
>
>
> > If anyone in this forum thinks that S-meter reading are 6db each with
all
> > the converters and preamps ahead of the receiver they are kidding
> > themselves!
> >
> > 73's de Jess - W4MVB
> > ----
> > Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> >
>
> ----
> Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
>










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