Monday, April 28, 2014

The Guerrilla AM Transmitter

Q1 - MPS2907 RS p/n 276-2023, or a 2N3906   I used one from the 15 pack RS p/n 276-1604
Q2 - IRF510   RS p/n 276-2072   - drill a hole, mount with a bolt and nut to
    the copper board, or to a little heatsink on the board, or your chassis.
    And use an insulator and thermal grease. This part gets warm.
R1 - 47,000 ohms .125 or .25 W   anything from 27K to 100K here is OK.
R2 - 10 Ohms, .5 or 1 Watt
R3 - 100 Ohms, .5 or 1 Watt
Low-cost ceramic disc capacitors are used.   But if you have some better silver-mica
or polystyrene types, go ahead and put them in this circuit.   And for C6,
a variable capacitor with a range of 500 to 1500 picoFarad is nice.
Or a 500 picoFarad or so compression trimmer, and then add a 470 pico-Farad
capacitor in parallel to it.

C1 - 100 picoFarad   RS p/n 272-0123
C2, C3, C4, C7 - .1 microFarad RS p/n 272-135.   For C2, C3, C4 this is a RF bypass
    capacitor, so anything .1, .47, .82 microFarad is good here.   C7 is a RF coupling
    capacitor, so anything from .01 to .47 or .82 is OK
C5 - 500 picoFarad   I used two .001 microFarad RS p/n 272-0126 in series.
    but anything from 470 to 680 picoFarad is OK here.
C6 - 1000 picoFarad (.001 microFarad) RS p/n 272-126

The inductors are made from Radio Shack p/n 273-102.   Un-wind the wire off,
then break the inductor core into two pieces.   Use two plyers and grab
it then snap it in half.   Make 4 inductors out of 2 cores.
L1 - 17 turns of the wire taken off of new inductor, wound in the center
    of this piece of core, and glued down.
L2 - Flyback inductor.   10 turns of the wire removed from the new inductor,
    wound in the center of this piece of inductor core, and you can glue it down.
    But putting AWG 18 or 16 would be a little bit better.
    And not critical on the turns count. 5 to 15 turns or more OK.
L3 - 7 turns of the wire that was removed. But better to use some AWG 18 or 16.
    Put this winding in the center of the piece of inductor core.
    Do not glue down yet.   This inductor with capacitor C6 determines
    the output power.
L4 - take the wire that was removed and wind it on the whole length of this
    piece of inductor core.   Or you can use a whole new p/n 273-102 here.
    Or any inductor with over 10 microHenries, and a low resistance,
    say less than a few Ohms.     So any of them oddball inductors
    on them toroid cores will be OK here.   L4 just establishes a zero
    point for the output RF waveform, after capacitor C7.
- - To test and tune up:   connect "RF out" to a 50 Ohm dummy load, or your tuned-up
radiating antenna system.   Connect the "modulating voltage" to the 13.8 V supply
along with the oscillator section.   Spread out the turns on inductor L3 to tune up,
for 6 to 8 Watts of power.   Then cut some of the wire off, so that you can wind it
in the center of the core, to get this 6 to 8 Watts of RF output.   On the 2 of these
transmitters that I have made so far, I have used 5 turns of 18 and 16 AWG,
close wound, in the center of this piece of the inductor core.

No comments:

Post a Comment