30m Phasing Rx

I recently found an old project that had been left in the junk box unfinished. It's a direct-conversion phasing receiver for 30m.

Inspired by my current binge-listen to the Soldesmoke Podcast https://www.soldersmoke.com/ archives (I'm starting at the beginning and listening to them all.. currently I'm at around Episode 30) I thought I'd restart the project and build it into the planned-for 30m CW transceiver. There's a 5W PA strip that's recently been used in my QRSS MEPT but I'll build a new PA for the MEPT and use the original one for it's original purpose.

I repaired a few broken wires and dry joints and the RX is working. I've checked that the phasing opposite-sideband rejection is working and given it a tweak to check that the adjustments are doing the right things. All looks good.

I'll document the circuit later

Here are some photos

There's a Makertube video of it receiving its first signals…

https://makertube.net/w/4xeject7Vtk6E9zxuJqxsd

Coming soon….

The basic format is

• Band pass filter for 30m
• RF amplifier
• Signal splitter to feed the RF ports of a pair of home-made passive 4-diode balance mixers
  • 
  • the 2 mixers are also fed with 90° I & Q local oscillator signals from an arduino/Si5351 IQ VFO
• The outputs of the 2 mixers is a pair of baseband audio signals in quadrature which then pass through the phase-delay circuits
• The 2 paths combine such that the audio from the unwanted sideband is cancelled and audio from the wanted sideband is presented to to an op-amp audio BPF centred on 700Hz.
• Then there's a audio amplifier that can drive a speaker.

After using it alongside my separate 30m TX 30m CW TX while testing the TX I found it very necessary to turn the volume down FULLY before transmitting, otherwise, un-muted, the receive audio is dangerously LOUD… that's fine as long as I remember to turn the volume down…. but after forgetting once, while wearing headphones, I don't dare risk it again!

I added a simple audio switch in series with the audio path, between between the post-BPF amplifier stage and the “top” of the volume pot.

I found the basic circuit at https://g4tgj.github.io/Audio-Switch/.

For the muting I hold the mute line high with 10k in the receiver and then the mute input is a “ground to mute” connection which is easily arranged from the TX QSK board.

It works well enough to both save my hearing and to provide a useful sidetone from the receiver during transmit, which means I don't need to add a sidetone circuit.

Page created : 16/07/26 22:57 BST

Page updated : 22/07/26 11:36 BST