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Monday, 8 February 2016

23cm - From a hilltop?


I mentioned a while ago that myself and Vince, G0ORC were planning to have a bash in the UKAC contests. We have a capability for 6M, 2M and 70cm but nothing portable yet for 23cm. So hence the project....

I bought one of these transverters:

and to go with it a PA kit from G4BAO:

Here's what I've made so far:

I used a toroidal transformer I had to create the PSU, the requirements are 28V for the PA and 12V for the transverter.

The transverter module itself looks like this:

and the PA, once constructed, looks like this:

Now, the first conundrum was how to test the RX path of the transverter given that my signal generator only goes as high as 1GHz.

What I realised was that my Spectrum Analyser can be set into zero span mode and that makes the tracking generator a fixed frequency. So I set the Spec An to 1296.5 MHz and hooked it up like this:

With the F-817 set to 144.5 MHz I have a strong carrier - so I conclude that the RX chain is working.

Now to test the TX chain - more tricky!

First of all I realised that I can tune the input and output of the PA using the Return Loss Bridge combined with the Spectrum Analyser. Here's the finished result on the input side (after some trimming in accordance with the assembly instructions):

And here is the output side of the PA:

So now to devise a way to test the whole TX chain, this is what I came up with:

Which kind of looks like this:

So we have the RF from the PA into the big block which is a Directional Coupler, the -30dB forward port is feeding the Spectrum Analyser via another 25dB attenuator, then on the antenna side we have 2 x 30dB attenuators to a 50 ohm load. The return loss of this lot is actually quite good and looks like this:

Now, I have tested the transverter without the PA and can see an output at the expected frequency:

There's much less attenuation in the chain for the test above, but when I try and set the idle current on the PA it kind of runs away. By that I mean that as the device heats up so the current drawn increases and just keeps increasing. I think this is because I don't yet have any suitable heatsyncing in place so have ordered something which I will have to wait for before I can continue.

So far, so good though, egh?

Here's our latest addition currled up with her Dad:

Local conditions.

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