Making the ARRL 3W CW Transmitter

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Making the ARRL 3W CW Transmitter

Postby VA7LAS » Tue Dec 13, 2011 4:27 pm

I'm going to try the Famous 3W CW Transmitter, apparently originally shown in ARRL magazine ( I have a couple questions:

First, how do you get 3W out of 12V? Assuming around Class C, that would give you a max RMS voltage of around 7-8 volts, which into a 50 Ohm load would be about a watt.

Second: is the text on how to wind L1 correct? It looks like the tap should be on the end connected to the collector, NOT to C1. Then L1/L2 and L3/L4 would be almost identical. (I assume the "cold end" is the lower end as shown in the diagram)

Oh, and one more: can I put in a reactance (capacitor?) in series with the crystal and "bend" the resonance frequency a bit? I have a 7050 MHz crystal and would love to get to 7055...

"Apart from that, Mrs Lincoln, how did you like the play?"
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Postby k8jd » Mon Dec 26, 2011 6:47 pm

That tap on the coil is to match the low Z output from the collector to the high Z of the tuned circuit. I have a MFJ QRP rig or two that put out 3 and 5 watts with 12 V supply !
73 from K8JD, SKCC 1395, Centurion 18, Tribune 12, Band Endorsements; 160, 80, 60, 40, 30M, 20, 17, and 10M

Ham radio is real Radio, CW is real Hamming!
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