G6GVI on 9cm (the 3.4 GHz band)


Some years ago, thanks to some loaned equipment from my friends Bob G8DTF and Dave G4MVU from the Bolton Wireless Club I made some contacts on the 9cm band.

Initially I was using Bob's downconverter (with a 144MHz IF) and his varactor-multiplier transmitter with my own SNA586 MMIC as a "PA" - but the x8 frequency multiplication (from 425MHz) meant that we were limited to "not-so-narrowand FM".
Then Dave loaned me one of his linear transverter systems, in which he'd converted a couple of AirSpan AS4000 WLL units to use a 23cm IF, which enabled us to make clear SSB contacts from Winter Hill down to his QTH.

Bob's varactor-multiplier transmitter mounted on the back of a phased array of 16x dipoles plus downconverter fitted with dual bi-quad The G4MVU transverter system, using a modified 23cm transverter for the IF

I was so impressed with this that I built a similar system for myself. But I used an IF of 880MHz (very close to the 850MHz originally used in the AS4000), which saved me having to change the VCO inside the unit - although I had to make a crude 880MHz "transverter" to go along with my 2m transceiver.
Here are some pictures of the project in progress:

Programming the PLL local oscillator in one of the AS4000 units from the PC parallel port Modifications to the AS4000 board

Testing my 880MHz transverter section The radome cover removed to show the patch antenna array

My complete 9cm transverter system ready for testing

I field-tested this during the August 2012 SHF UKAC session: my first QSO was appropriately enough with Dave G4MVU and signals were S9+20dB both ways.

Then after using it portable over the summer of 2013, I passed it onto Mark M0UFC to use in the SHF UKACs; he uses it with his FT817 rather than my IC202.

Then in 2017 I bought one of the new generation of C-band LNBs with a PLL oscillator. This downconverts 3400MHz to a "negative IF" (i.e. frequency-reversed) around 1750MHz, which can be tuned with a FunCube Dongle or RTL-SDR.

The PLL LNB mounted on my mast, alongside an Octagon LNB for 3cm

With this bolted onto my mast, despite an obstructed view to the South I was still able to detect the GB3ZME beacon on 3400.91MHz from Shropshire. My waterfall display shows the two frequencies of the beacon's FSK signalling, along with a slow HF frequency drift caused by my LO heating up and a more rapid LF shift due to the Doppler-shift from an aircraft reflection.

Detecting GB3ZME on the HDSDR waterfall

I'd set the "Swap I & Q" option in HDSDR to compensate for the "negative IF": therefore frequency increases from left to right on my display, and I can receive USB signals on "USB".

My original tests used the supplied "flat scalar" flange around the LNB, which is designed to provide a wide beamwidth to illuminate a prime-focus dish. However I've now built a crude conical horn to give better directivity (folded from 0.5mm sheet aluminium and secured in place by a pipe-clip).

The 9cm LNB fitted with my homebrew horn

I've fastened it higher up on my mast too, so now the beacon is clearly visible all the time, in brighter colours on my waterfall display - and I can even hear it through the laptop speaker!

Improvements in the system brought in a stronger signal from GB3ZME