QRPp

[N8TGQ]

Ham radio is the hobby of a thousand hobbies.
One of my favorite niches is building small milliwatt transmitters and seeing how far away they can be heard.

My ultimate transmitter does a mighty 250 milliwats on 7 HF bands. It started with an OXO transmitter kit from Kanga products. I added crystals from KC9ON at Third Planet Solar with a DIP switch to select band. Then I used a low-pass filter board from Zachtek to keep everything clean and legal.

I haven't actually made any contacts wih it so far, but get great spots on the Reverse Beacon Network. I'll be back out trying at the park as the warmer weather gets here!

 

[N8TGQ]

Don't know what happened to those pictures! They looked fine here.

 

[Ham4CW]

Don't know what happened to those pictures! They looked fine here.

What's wrong with them? They look OK here as far as I can tell.

As it stands they are inserted as thumbnails, then clicking on them once brings up the image viewer, and finally clicking on the images in the viewer zooms them to full size. Like I say, they look fine.

Ah, the 'venerable' OXO transmitter. I first came across the design in the G-QRP Circuit Handbook, published by the G-QRP Club in the UK. For those who are not familiar with the design it was created by George GM3OXX [sk] many years ago. There's a fascinating biography about George on the Lothians Radio Society website, you can read the article here: https://www.lothiansradiosociety.com/2017/10/10/silent-key-george-burt-gm3oxx-20-september-2017/

Here's the circuit diagram (from the Kanga version) of the OXO transmitter (click image to enlarge):


In your multi-band version, can you trim the crystal frequencies or are they essentially preset (determined by the fixed values of the components in the OXO)?

Also, how do you implement the receive side of the system? Do you run a receiver with its own independent antenna or does it share the transmit antenna via some kind of changeover mechanism?

73, Mark...

 

[N8TGQ]

What's wrong with them? They look OK here as far as I can tell.

As it stands they are inserted as thumbnails, then clicking on them once brings up the image viewer, and finally clicking on the images in the viewer zooms them to full size. Like I say, they look fine.

Ah, the 'venerable' OXO transmitter. I first came across the design in the G-QRP Handbook, published by the G-QRP Club in the UK. For those who are not familiar with the design it was created by George GM3OXX [sk] many years ago. There's a fascinating biography about George on the Lothians Radio Society website, you can read the article here: https://www.lothiansradiosociety.com/2017/10/10/silent-key-george-burt-gm3oxx-20-september-2017/

Here's the circuit diagram (from the Kanga version) of the OXO transmitter (click image to enlarge):
View attachment 1153

In your multi-band version, can you trim the crystal frequencies or are they essentially preset (determined by the fixed values of the components in the OXO)?

Also, how do you implement the receive side of the system? Do you run a receiver with its own independent antenna or does it share the transmit antenna via some kind of changeover mechanism?

73, Mark...

No, Mark, didn't add the capacitor to tune around the crystal frequency. I keep changing things on it so that may come next. I was trying for the smallest package I could for this try.
And the antenna switch is just clipping a lead from the receiver onto the antenna when receiving and disconnecting during transmit. High tech! I also have to remove power from the transmitter because the oscillator is running all the time.
It reminds me of my dad's station back in the 60s. He had to switch the transmitter, receiver and a knife switch for each over.
One difference though. The basement lights would dim every time he fired up the transmitter!

 

[Ham4CW]

Silly question maybe, but what does the "/B" signify?

I've not seen that appended to a call sign before.

73, Mark...

 

[N8TGQ]

/B is used by a lot of beacon stations to separate the beacon spots from their normal everyday contacts. The RBN allows you to also use numbers ("-1 or /1") also. It makes it easy to compare different antenna/radio setups quickly. Just have to remember which number goes with which setup.

The RBN plot above was actually to test a new antenna. It's an EFHW cut a bit long for 40m. Then I found the resinant point for each band by winding the wire up to the right spot and tying a knot to mark that point. So I can wind the wire to the right spot and have a full sized half wave for each band
I even added 6 and 2 meters!