Thursday, March 16, 2023

Bush 40 transceiver

Inspired by the VK3YE Beach 40, I have constructed the "Bush 40" which is a version tailored to The Australian outback. (Just kidding).

It is a direct conversion receiver and double sideband transmitter. I've replaced the VXO with a very simple, three component, VFO.

I'm joking a bit here too, it has an Arduino Nano, an Si5351 board, and a rotary encoder. On boot up it starts at 7.1MHz and you can tune up and down from there.

The mic amp, mixer, rf power stages and low pass filter are as per the Beach 40.

The receive audio stages are from the Soldersmoke High School DC receiver

Overall, this is a minimal design and the door is open to many improvements.

As you can see, it's a gadget of great beauty. At this stage the receiver is working but is quite deaf - I'll keep working on this.

Notes for future builds:

  • Use a larger baseboard so there's plenty of space for access to the boards
  • Always put a reverse diode on the relay coil - I killed an Arduino Nano presumably from inductive spikes on the power line.
  • Don't try to drive a mixer directly from an Si5351. (I was puzzled about why the balanced mixer was so far off balance when I switched from the VXO to Si5351, the reason is that the output RF is 0-3.3V not AC) A 0.1uF capacitor fixed this.
  • Building modules on their own boards for easy debugging is the way to go. Also, this means the successful stages can be re-used easily.
My thanks to many people including Bill, Paul, & Stephen for suggestions.


Bill Meara said...

Very cool Peter. Soon we may have to face the real possibility of two DSB/DC stations meeting on the air. Whenever we build DSB rigs, someone will warn us that two such stations can't work each other without some fairly severe distortion. We always remind them that it is HIGHLY unlikely that one DSB/DC station will ever contact another DC/DSB station on the air. There are just so few of them. For a while there I thought there were at max two of us in the world: Peter VK3YE and me!. But with you and Dean KK4DAS and others active, I dunno. Might have to watch out! I always loved it when some guy would tell me I was on the "wrong" sideband. "No," I would say, "I'm on BOTH of them!" This would really freak them out. I would tell them to just hit the button for the opposite sideband on their rigs. We would hear each other just the same. Have fun. Keep us posted. 73 Bill N2CQR

Peter Marks said...

Thanks Bill, and thanks for all your inspiration and help.

Yes, my local club is looking for a group project but, for the reason you mention, I would not suggest a DSB transceiver. Like you, I've had contacts in the past running DSB and the other station was oblivious.