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R: TS-2000 & preamps




----- Original Message -----
From: Perry Yantis <pyantis@compuserve.com>
To: Amsat-bb <amsat-bb@AMSAT.Org>
Sent: Friday, February 22, 2002 3:19 PM
Subject: [amsat-bb] TS-2000 & preamps


> I power my two down converters by getting a small box at Radio Shack and
> running 12 volts in from my power supply.
>
> Then I have two wires coming out that have 12 volts coming out.
>
> One goes up to the 2400 down converter and the other goes to my Hamtronics
> 2-10 down converter in the shack.
>
> This way one switch covers both for ease of operation.
>
>
> I have good signals on 10 m from the down converters (into 7/8 Heliax, 40
> feet long) and so I do not use the built in pre amp (it just increases the
> noise level) or the attenuator.
>
> This way my downlink signals are mostly loud but they do not move the s
> meter.
>
> Some hams use more gain and then have to attenuate at the shack.
>
> I did not want to go that route.
>
> So I never give anyone an S-9 signal report but my downlink signals are
> better then I have had using other satellites.
>
> Perry Yantis WB8OTH
>
>
> If you have a TS-2000, how are you powering and controlling your preamps?
I
> have to admit that my Icom's have spoiled me in that regard since they put
> the
> preamp power on the coax and switch it off at transmit.
>
> Anybody using a second 144-28MHz. converter to connect their Mode S
downlink
> to
> the HF receive antenna port on the 2000?  If so, are you tweaking the
28MHz.
> unit for less gain or putting an attenuator in the line?
>
> Dave Reinhart
> wa6ilt@amsat.org
>

Hi Perry and Dave

I use a second 144-146 to 28-30 MHz  high dinamic range converter and so i
receive 2400-2402 MHz tuning 28-30 MHz in to a well know and old Drake
R4-C HF receiver.

Inmy case,the conversion gain,including 2400 MHz preamplifier in focal point
 + 2400 MHz postamplifier + 2400 MHz converter antenna mounted + 144 MHz
converter located down in the shack is about 60 dB that is too much for the
R4-C receiver input because the noise level alone will be S 9 +20 dB or
more.

We dont need to much gain in front of the 28 MHz receiver because it is the
to be considered the fifth stage of the receiver chain.

In this case the low noise figure of the system from 2400 MHz to 144 MHz is
not deteriorated at all decreasing the signal level in front of the 28 MHz
receiver.

For this reason i have connected a 10 dB fixed attenuator to the 28 MHz IF
output of the 144/28 MHz converter ,than follow a variable 1 dB step
attenuator wich is switchable from 1 dB to 30 dB in 1 dB steps

Than follow a second fixed 10 dB attenuator connected to the 28 MHz R4-C
receiver input.

In this conditions the 144/28 MHz converter output as well the 1 dB step
attenuator and the R4-C receiver input all better sees an impedance of
about  50+j0 ohm

If the 1 dB step attenuator is loaded with a 10 dB fixed pad both in its
input and output than the 1 dB indications  are true figures and this setup
can be used for true sun noise,transponder noise or signal  strenght
measurements  using the S-meter

Since the R4-C receiver has the AGC OFF position it is possible to make the
above measurements even more accurately reading the AC voltage ratio at
the audio output of the HF receiver

During operation on AO40 i adjust the attenuator to set the noise level of
the system to an indication of S1 on the R4-C  S-meter

Than i tune the AO40 beacon and i read the new S meter indication.

This indication has no meaning at all in terms of  S units.

Now i  switch the 1 dB step attenuator increasing the numbar of steps until
for the beacon signal i read again S 1

If  i added 27 dB,wich is my case, it means that my receiving system  has
the capability to receive the AO40 beacon with a  (S+N)/N ratio of 27 dB

This is why sometime an old 144/28 MHz converter in the joukbox in addition
to an old 28-30 MHz HF receiver can do a nice job for serious noise and
signal level measurements.

The same is not true reading directly the S-meter indications of a 144 MHz
receiver if it is used as a second IF receiver because the 2400 MHz
converter in front of it make the S meter indications completely
uncalibrated.

I hope this help a bit.

73" de i8CVS Domenico


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