A Smeter for your satellite receiver :
to evaluate the relative received levels

 

Introduction

To be able to evaluate the relative level of a received signal is always very useful : to aim an antenna, to optimize its polarization or to compare the received signal strength from various correspondents, the small modification described below will be very useful. It is not a true l S-Meter, because for reasons of simplicity, one will limit itself to measure the AGC voltage of the satellite receiver tuner by means of a traditional digital voltmeter.
In this point, we are (almost) sure of only one thing: the measured voltage and the signal strength vary in the same direction !

Modification

Caution: inside the receiver cabinet some accessible parts are to the main voltage. To achieve the described hereunder modification, you must take the suitable precautions.

- after having unpluged the main, open the receiver cabinet,
- identify the receiver tuner: it's very simple, it is usually bound of the F socket on which is connected the coaxial cable to the satellite LNB,
- unscrew the screws that fix the printed circuit of the receiver on its metallic frame,
- turn the printed circuit and localize the connections points of the tuner on the printed circuit,
- isolate the printed circuit and the different active parts from accidental contacts, by means of pieces of wood or cardboard,
- connect the common wire of a digital voltmeter to the metallic frame by means of an alligator clip,
- switch the voltmeter on the 20 V or 30 V DC range,
- reconnect the receiver to the main, very carefully,
- test the different connection points of the tuner on the printed circuit until you localize a point where the voltage varies according to whether the satellite LNB is plugged or no. Typically, the voltage varies from a fraction of volt to two volts,
- unplug the main again,
- bore two 8 mm holes on the rear panel of the cabinet to fix two 4 mm banana sockets,
- connect by means of wires the banana sockets : a wire to the ground, a wire for the AGC voltage,
- to avoid to introduce some troubles in the receiver, it's prudent to put in series with the AGC wire a 10 kohms resistance.
-.... and of course don't forget to close again the cabinet, with the screws you won't have lost during the time (! )

Photographs   

The connections to the receiver :

(click to enlarge)

The connections to the banana sockets and the 10 kohms resistor :

The rear panel of the receiver :

 

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