Hi All,
Does anyone have floating around in their books a circuit for the
following
Deviation, to be able to get a readout of the amount of deviation into
the repeater RX
****
From a point in the receiver take audio which is squelched amplify it with
an Op-Amp circuit, to prevent loading the take off point, rectify it and the
resulting DC Voltage can drive a meter or with a resistor to ground you can
then sense the voltage drop with an A/D converter to present it to the
controller. You will have to calculate, or determine experimentally, the
value of resistor etc. to get the resultant voltage to represent the proper
amount of deviation. If you use a meter, keep in mind that the mechanical
demping effect of the meter prevents it from giving you a true peak reading.
Use a circuit with a fast attack and slow decay constant to keep the meter
reading from bouncing all over the place.
Freq. offset, I understand there is a way to get a reading so that one
can tell how far off freq. the incoming transmission is.
***
All FM discriminators have a point in their circuit where there is a D.C.
Voltage representing the frequency offset from carrier center. Usually, but
not always, there is a point that gives 0 Volt, compared to ground or other
reference. This Voltage then will become either positive or negative when
the carrier deviates from centre. You can again use an Op-Amp to buffer
this and drive a meter or ADC.
Current, I have a circuit that is a shunt, so to read the amount of
current there is, but how do I get to tranform it to a DC voltage so the
controller can read it.
****
As mentioned before, current becomes a Voltage measurement if you measure
the drop accross a resistor. This can be presented to an ADC. Good sources
to get information on circuits are ARRL handbook, manufacturers manuals to
find the audio and DC Voltage take off points. etc. Application notes for
Integrated circuits used as IF amps, squelch circuits Fm discriminators etc.
are a good start.
73 .. Tony...VE3DWI
