John's homebrew pages

A single board 23cm (1.3GHz) transverter with 144MHz IF

As I have gradually built up a bit of experience in the microwave bands, I have been thinking about a nice project which could help a lot of other people to get going quite easily, fairly quickly, and most importanly (for me!) cheaply.

There are quite a few designs for transverters for 1.3GHz / 23cm on the web. Very early on I came across this design by Rick Cambell KK7B which was a great inspiration and stimulus to getting going myself on 1.3GHz - it showed that it could be done easily. I ended up with transverters that had to be tuned (Rick's is a no-tune design with printed filters) but even that wasn't too hard in the end. I also found the designs by Paul Wade W1GHZ very inspiring.

However, these designs are not truly single board - they need an external local oscillator, which is the really key component in a transverter. My recent experiments on 2.3GHz and 10GHz have led me to the use of synthesised local oscillators, stabilised by tiny temperature compensated crystal oscillator (TCXO) modules. These have been working very well indeed for me; they are very compact, and so I thought I would try to incorporate one into a board for a simple 1.3GHz transverter.

Design requirements

The basic requirements I've been thinking of are:

  • cost - it must not use expensive components
  • availability - it must use components that are easily available (not stuff long gone from eBay or found at rallies!)
  • weight - it should be lightweight, for hilltopping (e.g. SOTA)
  • size - it should be compact, to fit in a rucksack along with all the other clobber, and preferably fit in a standard, easily available box
  • easy to use - simple connections to a small transceiver, even a hand portable FM unit, and a simple antenna
  • versatile - it should be usable in its simplest form, but also have the option to be set up to drive a PA and use a preamplifier

I have been thinking about this since about October 2011, gradually jotting down ideas. I did some tests of a discrete component VCO and a band pass filter in August 2012, and the success of these meant that I thought it worth continuing with a design.

There is more to be added here about the design and the build, which will come in due course.

By August 2013 the receive side was built, and it worked; here's the result. The bit of red wire sticking up from near the centre of the board is the antenna which allows me to hear the local GB3EDN beacon very easily!

23cm single board transverter - Rx built

I found a few little errors on the board and in the design as I built the prototype, but got the receive side working fine; I found a screen over the VCO helped keep things stable. Problems started once the transmit side progressed into the amplifier and filter chain. I had very few problems with this on the 13cm transverter, even with similar simple bandpass filters, but was not attempting to get the power up very much. Here I found that I needed to add screening over the filters as I progressed up the amplifier chain in order to keep things stable. However I was unable to complete the chain and maintain good stability and enough power. This was a bit disappointing! However it enabled me to integrate everything into the box and get a good idea of what should be possible with better screening. Here's the prototype (with removable screening lids taken off):

23cm single board transverter - prototype

I decided that, rather than trying to fix the prototype, I would revert to a design with much better screening over the individual sections of the design - LO, receive side, transmit side, and a separate PA. I will build these sections as individual modules (though they could be incorporated on to a single board) to make build and test easier for me.

Here's the new LO module ready for construction (August 2014). Each module will have its own voltage regulator, and will have coax connections (can be SMA or SMB) for interconnects to the other modules. I'm hoping I'll be able to keep things stable this way!

23cm single board transverter - prototype

Next - trying out my new screening ideas.