My main effort for the May UHF/SHF contest weekend this year was to activate IO51 on 3cm (10GHz). I had tried to do the same last year but discovered a problem with the transverter’s local oscillator (LO) producing too little power, meaning the activity had to be aborted. Since then, with the help of John EI2FG, I had fixed the LO and everything seemed to be working fine.
Unfortunately, I can only erect the 3cm station on a temporary basis and it is quite a lot of work but, if I’m going to try it at all, the SHF contest weekends are the time to do it! Luckily I had a few contacts which made it worthwhile – in fact I had more success on 3cm than on 70cm where (admittedly with very little time spent there) I worked the one station I heard all weekend…
I have a decent setup for the 3cm band, even if it is getting a bit old now, based on modules from G3WDG. A few years ago I replaced the original LO with G8ACE’s OCXO, along with a CT1DMK reflock II that allows the LO to be disciplined (i.e. kept accurate) by an external 10MHz reference that I can supply from a Trimble Thunderbolt GPS-disciplined source. The IF is at 144MHz using my trusty IC275E as a driver and the output power on 10GHz is 10W from a solid state amplifier. The whole transverter is contained within one box:
At 144MHz I also split the receive line two ways, feeding one to the IC275E and the other to a 144-28MHz downconverter connected to an SDR-IQ: This gives me up to a 190KHz-wide display of the band, such as this example (20KHz-wide spectrum, the bright colours are my tx) showing GD0EMG’s signal with about 500Hz drift:
My 10GHz antenna is a solid 1.2m diameter prime-focus dish, using a Procom feed horn. I’ve added a small amount (perhaps -3 to +16 degrees) of elevation control with an 8″ actuator for levelling and a modified Lidl digital spirit level for sensing.
The transverter is mounted directly behind the dish to minimise losses and, with all the cables, the whole lot weighs a “ton”! I use my homebrew mast originally intended for 2m portable EME operations to get everything in the air:
Signs were very poor for any extended tropospheric refraction over the weekend but 10GHz is quite readily propagated by rain-scatter which, incidentally, is why weather radar generally uses a similar frequency in the X-Band. There was certainly plenty of the wet stuff about but unfortunately there were two problems: Firstly, there was far too much rain, which completely absorbed any signals (have you ever lost your satellite television, at 11GHz, during a rain storm?); and secondly the rain was in the wrong place most of the time – it is very frustrating having a block of rain to the north-west, when all the activity is to the east!
On Saturday many attempts set up via the ON4KST Microwave chat failed, but finally I managed a contact with GD0EMG (IO74QD, 344km) – the only one on that day. This was quite a relief because, without any local beacons, there was always going to be some uncertainty about whether the system was working or not. The signal was not too strong but actually sounded better to me listening on the IC275E than the recording taken from the SDR IQ Data file, which is below, along with the rain radar at about that time:
|GD0EMG (IO74QD, 344km) via rainscatter at EI3KD (IO51vw). The frequency was manually tuned to correct for signal drift|
On Sunday, once again, many attempts failed with the rain having cleared early on. However, at around lunchtime an area of showers started travelling up the Irish Sea from the southwest and crossed mid-path to Ralph, G4ALY (IO70vl, 323km), resulting in a great signal:
|G4ALY (IO70VL, 323km) via rainscatter at EI3KD (IO51vw). Practically zero drift.|
The same group of showers continued on a north-easterly track, but unfortunately didn’t quite get to the right place to make a contact possible with The Bad Weather DX Group (!) M0WXB/P (IO81xu, 424km), although we did hear signals both ways at various times. However, I was lucky to catch Neil, G4LDR (IO91ec, 466km) just in time to complete a contact, albeit with weak signals:
|G4LDR (IO91EC, 466km) via rainscatter at EI3KD (IO51vw). Practically zero drift.|
And that was it! Quite a lot of work for three (and a half) contacts but I was delighted… At least it proves the 3cms gear is working and I’ll be watching out for further opportunities to get it “on the air” 😀