Category Archives: QRP

What is a redpitaya?

Doing a lot of home construction is helped by having a heap of test equipment. There are several ways of getting that; take a risk on eBay and buy old stuff, build your own or get a redpitaya.

It claims to be able to work as an oscilloscope, signal generator, spectrum analyser, Bode analyser, logic analyser basic, LCR meter and vector network analyser.

If it can do all then it is truly revolutionary, and I want one! It is not cheap but if you add up the costs of the single instruments it replaces then it is definitely NOT expensive.

Using SMD – part 1

Why do I like using SMD? Let me explain, I began making radios using valves, it was all there was at the time. When I started work in the industry the first training courses were on valves and how they worked. Then the transistor came, then integrated circuits followed by surface mount devices, SMD. I guess I have followed the technology.

It is easy to be overwhelmed by progress and stick with what you know but there are many advantages to using SMD:

  • individual components, resistors and capacitors, are very cheap
  • many older devices are no longer available as wire ended e.g. the SA612
  • PCBs are smaller due to high packing density
  • high frequency boards are easier and cheaper
SI5351 board

An SMD VFO module

Above is an SI5351 board (ready made apart from soldering the SMA connectors) it is just 30mm wide and can used with an Arduino to make VFO with 3 programmable sine wave outputs. Current cost is less than £5 on ebay plus the Arduino.

You might need some new tools like a magnifier, fine tipped soldering iron and good quality tweezers. There are more including heated tweezers and a hot air gun for component removal but they can wait for a while.

So, my advice is do not be put off and have a go. Find a simple kit to practice with and then progress to more complex circuits. It helps if you know something about how SMD components are sized. Srat with the larger sizes and work down.

1206 and 0805 are popular SMD sizes

This is another good one to print out.

Over the coming month I will add to this series of posts and share some of the projects I am working on which include: a remote tuner, vector network analyser (VNA), wide range VFO/signal generator, a switched attenuator.

The antenna

The antenna is back up after 6 years! Nothing fancy just an inverted L at about 11m (~35ft) and around 38M (125ft) long. Still need to put in a counterpoise in the lawn but the ground is rock hard after weeks of drought, so it will have to wait.

Also need a remote tuner and plan on making one based on an Arduino.

I have a nice waterproof box that housed a commercial tuner to house it and will probably make it solar powered to avoid have to DC up the coax. Hope to get the coax in this week, it is something like a 40M run of RG-213. So, work to do before winter!

A scratch build Wilderness radio SW-20

This is an amazing build of a favourite of mine, the Wilderness radio SW-20. It shows just how neat and effective ‘ugly’ construction can be. In my opinion it is far from ugly!

I would love another but they are no longer available. Maybe this is what I should do over the winter – build one!

It is interesting that he started with the case and cut the copper clad board to size. It seems like a very ordered way of working.

A Scratch-Build of N6KR and Wilderness Radio’s SST for 20M

I had one of these radios a few years back and made many contacts on it. I did some mods but cannot remember what the function of the extra knob on the left side.

QRP does work!

Time and time again I see the trite remark that life is too short for QRP. Well, QROers you can do amazing things with very small amounts of power! Oleg Borodin, RX3G and Leonid Bovin, R1LB have completed a QSO on 14.060 over a distance of 970kms with each using 80mw. Congratulations to you both for keeping real amateur radio alive.

Life is too short NOT to try QRP!