G6GVI on 13cm (narrowband)


As a result of a conversation with Andy G1HBE and John MW1FGQ at the start of 2009, I became interested in 13cm narrowband operation (my only previous operation on this band was with wideband FM-ATV equipment).

My first step was to acquire one of the Chorus MMDS downconverters which Andy was using.
This has a PLL-synthesized LO, which I moved down to 2176MHz to create a 2m IF (the modification entailed changing the reference crystal to 8.5MHz, and adding a small capacitance to the VCO tuned circuit).
The first signal which I received using this was the 16th harmonic of my 2m handie, just to check that it was working! But as my home QTH is surrounded by higher ground, I thought that all my 13cm contacts would probably be made when operating portable from the nearby hills.

I recorded my first success on 24-Jan-2009, when I received MW1FGQ's NBFM and USB signals at 59+ from Winter Hill, at a distance of over 60km.
John was using just a few hundred milliwatts into a selection of home-made antennas, and we used 4m FM for talkback.
I've since tried to hear him from home, but with no success.

My home-made Tonna-clone 13cm yagi fitted with the modified Panorama LNB G6GVI/M on Winter Hill operating cross-band with MW1FGQ in January 2009 - Westward, look, the land is bright! The IF section consists of a bias-tee (in my lap!) and an FT817 to tune the 2m IF

Then in 2010 I modified the internal "hairpin resonator" RF filters to extend their passband further into our Amateur band (they were originally designed for 2.5GHz of course). Having done this, I was delighted to hear a thumping signal from GD0EMG during the May contest weekend.

And then in June 2010, I managed to pick up John's 0.5W signal from my home QTH in the centre of Bolton. I had my homebrew 24-ele loop-quad at the top of my mast, with the downconverter hanging below it (in the plastic bag!). The other aerial is my homebrew 12-turn helix for 23cm.
I was also able to hear a faint signal from G8DTF, reflected from some of the tall buildings in the centre of Manchester.

The 13cm receive system on top of my mast at home

And finally, on 12-July 2010 (nearly 18 months after our first one-way test), I managed 2-way QSOs on FM and SSB with John MW1FGQ from Winter Hill, using an old G8LMW transverter which had been donated to the Bolton Wireless Club by Bob G8DTF.
I'd just re-built this transverter into a fresh enclosure, but its output was only around 10 milliwatts!

The rebuilt G8LMW 13cm transverter: LO and RX sections The rebuilt G8LMW 13cm transverter: TX section

I continued to have problems with this transverter, so for the start of the new 13cm UKAC Contest in 2011 I brought my receive converter back into action, to see what I could hear from my home QTH in the centre of Bolton. I thought that I'd struggle to hear anything at all, but as well as hearing Bob G8DTF no matter where he was beaming, I also got strong signals from Tony G4CBW near Stoke.
But the biggest surprise was to hear G8OHM in Birmingham and to detect a CW signal from G0MJW near Oxford. The latter signal came via an aircraft-reflection, and I could see the Doppler-shift receding by nearly 200Hz in 20 seconds:

Spectrograph showing G0MJW's Doppler-shifted signal

Then in the Feb-2011 session, I also heard MW1FGQ, GW8ASD, G0MJW (Oxford), G8OHM and G3VKV (Cheltenham) all on SSB.

I got the transverter back in action and took it out portable over the "summer" sessions, usually making 5 contacts with the meagre 50mW output.

Then in September 2011 I acquired some more G8LMW boards to make up a transverter of my own. For the first few months I was using the G8LMW unit for transmit and the MMDS downconverter on receive, with separate antennas and IF radios - so I needed to listen on headphones to net my transmitter onto my receive frequency (a bit like working through a satellite transponder!).
And thanks to Bob G8DTF, I was able to add a "PA" with around 2W output, so I was actually able to make a few QSOs from my home QTH in UKAC sessions - which contributed to my Runner-up Certificate for the 2011 event!

My distributed 13cm station (not forgetting the other half of my receiver which is tied to the mast beneath the antenna! Runner-up in the 13cm UKAC 2011, using QRP from LMW transverters

By June 2012 I'd got the RX side of my transverter working, and so was back to the sanity of a single IF radio!. Initially I was just using a satellite "cable booster" as my receiver RF section, but have now cobbled together a better front-end.

My 2-stage front-end includes an ATF581 FET and a MMIC. I used a PCB which was designed for 0402 components, but somehow managed to squeeze my 0603 parts on in their place!

But in September I found that I could get a big improvement by adding a post-mixer gain stage (in the 2m IF) of the transverter, and now I can hear some more distant signals. This was very helpful in the October SHF UKAC session, when I was able to work G4BEL (220km), G4KIY (192km) & G8OHM (134km) all within half an hour!
And I contined to use this throughout the 2013 UKACs - from home in the darker months and out portable from the hills over the summer.

Then in 2014, following OfCom's Release of part of the band and the subsequent shift of the 13cm UKAC sessions into the night-time, I gave up portable operating myself and loaned my gear to John G8PEF, who was becoming keen on SHF for the first time.

In December 2014 I obtained a Notice of Variation to use the new allocation of 2300-2302MHz. Then in 2016 I began experimenting with an SDR transceiver for use there and in our original 2320MHz band.

In 2019 John returned my LMW transverter. After using it with dual antennas again for a few months, I finally got around to rebuilding my masthead LNA to include an Axicom HF3 relay, so now I can share a single antenna for Tx & Rx (but still keep two downleads to connect to my transverter).
When I first tried this, the preamp was oscillating - but I soon managed to tame it by adding a couple of brass pillars inside the box, to improve the grounding around its input.
Having the same antenna for both Rx and Tx has made it much easier to peak up on other stations: living in a valley, I find that a lot of my contacts are via reflections, rather than on the "correct" beam-headings!

Now a single antenna is switched between TX and LNA LNA/switch unit mounted on the mast

If you'd like to try a sked on 13cm, then please get in touch.