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Friday, 10 March 2017

13cm Antennamabob


You may recall back here I installed a 13cm antenna on the mast, and here I built the 13cm VLNA from @DXING G4DDK. The VLNA is now mounted masthead with the associated switching and a separate feed for TX and RX as I described here:

I've also recently acquired myself a much wider frequency coverage Spectrum Analyser; it's a very old HP8593A which covers up to 22GHz and came from here and has nice things like a 2 year warranty:

So, using the Signal Generator I made back here, and a cheap Chinese directional coupler being used the "wrong way" round;

like this:

I can leave the Device Under Test port open circuit and see the amplitude of the signal from the sig gen on the Spec An. If I then connect the antenna to the DUT port and calculate the difference between the open signal and the signal with the antenna connected - that should be the return loss in dB:

So apologies for the really rubbish photo, but the higher peak is with the DUT open circuit - so a really pants SWR and the lower peak is with the antenna connected. That's a difference of about 30dB. So using the maths we established back here we can deduce that the SWR is about 1.07:1 - which is bang on the money.

I was rather hoping I could hear the Leicester beacon GB3LES on 2320.955MHz - but I can't. So there may be a number of reasons for that - including my poor N-Type connector soldering, so I will have to look further.

But progress none the less!


The Leicester beacon has a fixed antenna beaming 160 degrees from its location - that's almost completely in the wrong direction for me! I've tuned to the Telford beacon on 2320.870MHz and I can hear the beacon just fine - RX working!

Local conditions.

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