One the stumbling block for QRP enthusiasts, interested in building AM transmitter related projects is need of modulation transformer. I have simple solution for this. You can use audio output transformer from old radio receivers.
Thursday, 3 March 2011
Wayne Burdicks modified Neophyte receiver for shortwave reception
The modification described here provides coverage of 6O·meter tropical broadcasting (4750-4995 and 5005-5060 kHz), the standard-frequency-and-time allocation at 4995-5005 kHz, 49-meter international broadcasting (5950-6200 kHz) and frequencies used by the aeronautical mobile, maritime mobile and fixed services between 4520 and 6250 kHz.
Wayne Burdick put his Neophyte receiver on 15 m and modified its audio response for better CW reception as shown here. The parts associated with U1's pins 6 and 7 serve as frequency-determining and feedback elements in U1's local-oscillator subcircuit; C1,C2, RFC1 and RFC2 reduce the receiver's audio response above 1 kHz; and R1 and C3 reduce hiss by decreasing U2's response at higher audio frequencies.
T1's secondary winding consists of 26 turns of #24 enameled wire on a T~50-6 toroidal core; the primary is 2 turns of #24 enameled wire over the secondary'S pin 2 end. l1 consists of 26 turns of #24 wire on a T-SO-6 toroidal powdered-iron core; RFC1 and RFC2 are Mouser Electronics 43LJ4l0 chokes. All electrolytic capacitors are 16 V.
See Fig and Table,. C21, a 220-pF capacitor, and S2, an SPST toggle switch are new components. S2, BAND, switches C21 in parallel with the original Neophyte's ClO to select added "low-band" option.
Simple QRP Transmitter
The figure shows very simple QRP transmitter for novice ham operators.The circuit misses morse key or modulation input. You can easily modified this circuit both for CW and AM operation.
Simple RF Crystal Tester
This circuit will test crystals from 1MHz to 30MHz. When the crystal oscillates, the output will pass through the 1n capacitor to the two diodes. These will charge the 4n7 and turn on the second transistor. This will cause the LED to illuminate.
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