Monday, August 26, 2013

ગૂફતગૂમાં રાત ઓગળતી રહી;
ને શમાઓ સ્પર્શની બળતી રહી.
સ્વપ્નમાં એકાંતનો પગરવ હતો;
રાતરાણી ગીત સાંભળતી રહી....

Monday, August 12, 2013

Pulser, Criket

        Sometime during the testing phase of tx it is requied that it be keyed on and off to tune it. If we key with one hand try to tune the prototype it become impossible. So, some sort of cheap repetating keying device is needed.
       An Astable multivibrator comes to the help. A transistor can switch on the relay and relay can control the PTT or CW tx.

     The tx during the experimental  build stage should  not be connected to the radiating antenna. Tx should be connected to the dummy load and if signal is required a small  1 foot wire may be connected to dummy load and hope that will produce the sufficient signals in near by radio.
1. Cricket:-
cricket, produces pulsed audio train
This is oscillator circuit which produces the af tone. q3-q4 is a AF osicllator. q3 is switch which provides the power supply to audio oscillator according to the low frequency multivibrator based on q1 and q2. 

audio output is taken from c5.

It does not key the transmitter. i use it on test bed to inject the audio to the dsb modulators and monitor the rf on comm. rx. so i dont have to say "hello test hello test". it produces the tick tick sound like a cricket so thats name. q1-q2 are bc547, q3,q4,q5 are bc557. c1,c2 are 10mfd,25volts. c3,c4,c5 are o.1mfd. it can be powered from 12 vdc. Please not that due to pnp,npn power supply needs to be reversed.