Saturday, March 30, 2024

Multi-band antenna change - back to the Off Centre Fed dipole

Lucky to have the space for this sort of thing, I had put up a full wave "sky" loop for 80m. It was suspended from a number of trees around the yard but not very high and it came down in the wind a bit. I still have mono-band dipoles for 80m and 40m but it's nice to have a multi-band antenna for general listening without switching. 

Yesterday I pulled down the loop and replaced it with an Off Centre Fed dipole for 80m and above. In the picture to the right it's the front most antenna hanging from my antenna tree so up pretty high.

The wire lengths are: Short side = 39.5 feet, Long side = 94.5 feet suggested by Palomar.

Happily it resonates quite well on the first go with a 4:1 balun as usual. Quite usable without tuner on 80, 40 & 20m.

Before I took down the full wave loop I took this screen shot from SDR++ looking at 40m:

Here's a screen shot of SDR++ with the same gain settings on the OCFD:

Signals, and noise, are greater. 

Friday, March 15, 2024

Handy breakout board for Raspberry Pi Pico

Just picked up a few of these breakout boards. I'm not sure that I like the screw terminals but it is handy having LEDs on each GPIO pin.

 I'm really getting in to the RP2040 and recently ordered some boards with USB-C connectors.

MicroPython is great for most things, there is support for the Arduino runtime library and I can drop down to the native toolchain if required.

Sunday, March 10, 2024

A pleasant trip north via "The Dish"

A friend had some boxes of yachting gear left in Melbourne and I kindly agreed to drive it up to him at Dorrigo NSW. Along the way I visited John, VK2ASU, Merv and Dallas, VK3EB. 

On the way back I dropped in a Parkes and took another look at the CSIRO Dish.

It was a long drive in the Jimny and to avoid the high noise level I listened to podcasts in noise cancelling headphones.

I stopped for two nights at Port Macquarie and was interested to note that a podcast I listened to later, which was obviously downloaded while I was there, had local Port Macquarie targeted ads inserted in-line.

The return trip was more rapid and the final run from Dubbo to Drummond was a marathon in hot conditions.

It was good to get away and to catch up with friends. It's good to be back.

Here's a circularly polarised log periodic antenna.

Here's an Apollo 11 S band OMT:

S Band is 2.4–2.483 GHz. I think an OMT is an Orthomode transducer which is a waveguide component referred to as a polarisation duplexer.

Here's an impressive bit of work, a C30 Converter: