First QSOs With New TX/RX Project

I'm building the companion TX 30m_cw_tx for my recently completed 30m phasing RX 30m Phasing Rx

It uses a 4-stage PA strip consisting of

• Class-A amp : 2N3904
• Tuned Class-A amp : 2N2222
• Tuned Class-C amp : BFY51
• Class-C MOSFET PA : IRF150

Driven from a SI5351 VFO it produces around 5.5W with 13.8V on the drain of the final MOSFET amp.

I added a “QSK” board to handle

• antenna Changeover relay
• TX VFO Enable (delayed by ~20mS to allow the relay to pull-in first)
• CW Keying of the first two amplifier stages

I had some problems with a 7-pole Butterworth LPF I'd added in place of the simple 5-element “Half-Wave” LPF of the initial build. On keydown there would be a strange variation of output power, up to 6W and down to 4W, then wandering around over time. Initially I thought it was the MOSFET changing its behaviour as it warmed up. But swapping back to the original half-wave filter cured it completely. I assume one or more of the small ceramic capacitor was unable to handle the voltage. No such problem with the components used in the simpler LPF.

Yesterday afternoon I called CQ a few times and was answered by a weak, but readable signal of ON4XMJ who added QRPp to the end of his call to show he was running 1W or less. Made my 5W seem overkill!

We exchanged details - My RST to Xav was 449 and he gave my 5W signal a report of 569

Xav was running 500mW only, so 10dB down on my signal. I'm really happy that my simple homebrew receiver could copy him, Xav was also using a home-brew rig.

https://www.on4xmj.net/

Here's my TX, spread over the bench, at the time

A while later I had my 2nd QSO, this time with Wang DK4AN - also QRP at 5W.

Later in the evening I did some more modifications to the TX - adding a variable PA voltage, via a LM317T voltage regulator, so that I can easily vary the output power between 0 and 5W.

I need to think about boxing it up.

And adding a Mute circuit in the RX, fed with a mute signal from the QSK board, so that I don't have to manually turn down the RX volume during transmit. A pair of 2N7000 should do the trick?

All good fun.

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