24-April-2018 SHF UKAC

I started on 3cm & moved to 13cm later. There was a fair bit of rain about and I think this favoured the northern stations. I worked several stations for the first time on this band: David G4RQI, Mel G8EOP/P, Pete G4CLA and John G3XDY. So this contest broke my personal record for 3cm and I finished with 10 contacts. Nick G4KUX was the strongest I’d ever heard him. I worked Peter G3PHO for the second time; rain scatter this time, not snow scatter! I wonder if the snow has gone now? It was only 3 weeks ago at the beginning of April that I was shoveling snow and ice from the road outside.

1804243c

I started 13cm rather late. Denis said I was easier to hear on 3cm. I had some sort of cable connector fault on the 10m attenuator (K3 on 10m -> attenuator -> MM transverter ->70cm -> SGLabs transvertor). The attenuator ensures that I don’t overdrive the transverter chain. The “early” finish meant I could get to bed at the usual time.

18042413

17-April-2018 23cm UKAC

Conditions seemed pretty flat, but I managed to accumulate 30 contacts with Conrad PA5Y my best DX (longest distance), worked using CW/morse code.

It was nice to have the SSB Electronics LT23S transverter back on the air again. I used the old Bob Platts pre-amp; it seems to have some protection against inter-modulation products caused, I suspect, by whatever the Crosspool radio/TV towers are broadcasting.

18041723

LT23S transverter erratic power fault

I had noticed during the January 23cm UKAC that the power output reading was erratic. At the time, I wondered whether the snow on the Wimo antenna was causing some loading problems, but later tests showed the antenna, feeder & relay were OK.

I took the transverter apart & found no obvious problem. All the connections seemed good & both the internal relays were OK. The power jumped up & down to me tapping the circuit board.

With a probe, I gently distorted the board in different places & watched the front-panel power meter. I found the most sensitive spot was near to T12 (a BFQ34T) and the drive pre-set pot. The pot did not seem to be noisy. Pressing on one of the transistors metal tape connections seemed to cure the problem.

I thought perhaps a dry joint had developed. I scraped the solder on the connection, dabbed a bit of liquid flux on and then ran a bit more solder on. Problem fixed!

I suppose the driver transistor generates some mechanical heat stress and perhaps the solder had fractured.

I’ll try the transverter out in the April 23cm UKAC.

6-April-2018: 6cm ATV test with Barry G8AGN

I lashed up the transmitter & receiver with the horn, an SMA coax relay and a sequencer to make a basic transciever. I added a PTT switch to trigger the sequencer, SMA relay & transmitter. I leave the power on to the receiver so that I can monitor the transmitter. I had a small screen for display.

Initially at 1500 GMT we tested across the top Redmires reservoir.  The kit was all a bit “loose” at my end. I held the horn box & pointed it over the open car door towards Barry. Direction was not critical. I attached the camera to the car door with a bit of paper with G3YJR inscribed on it. We used 5.665 GHz. We both received each other P5.

Then Barry retired to Roper Hill & I drove over to the Crown & Glove pub (the “Top House”) car park at Stannington. This path was a bit over 4km.

Direction had become critical & video squelch a nuisance. At 1600 GMT, when I had a picture of Barry, it was good. Call it P4, as it easily flipped away when off target.

So signal gets through the box into the horn. I’ll need to do something about the video squelch. I’ll need to sort out a control/monitoring/camera box & a connecting umbilical cable to the transciever. Then I can mount the transciever on a dish.

The Roper Hill to Crown & Glove path looked like this:

Roper_Hill_to_Crown_and_Glove

So it was line-of-sight.

Incidentally, the Crown and Glove was looking good. It had a decent menu, some excellent real ale & they do a good pot of tea. The car park is a good VHF/UHF/SHF site.

 

A horn antenna for 6cm PAL TV

Barry G8AGN and a few others hereabouts are experimenting with little Chinese TV modules & I thought I would have a go too. These are nominally 5.8GHz modules, designed for drone/helicopter use, so very compact & light weight. The transmitter module I’ve bought is rated at 0.6W. There is a useful overlap between the available channels & the 6cm amateur band. Apparently the BATC use “channel 33”, 5.665 GHz for these modules. (More info from the BATC). The transmission bandwidth is about 27MHz wide. I seem to remember the old 625 line broadcast TV channels were 8MHz each? Maybe the modules allow higher definition?

I’ve never tried the 6cm band & I’ve never tried amateur television either.

I took the opportunity to make a horn out of copper sheet. I used a design from  Brian G4NNS’s website. See “Details for feed horns…”.

I used 0.5mm thickness copper sheet & marked it out with a marker pen according to Brian’s template. Then I cut it out using tin snips (metal shears) & bent the pieces on the bench edge, on the vice & with pliers. I found the resulting two pieces a bit fiddly to assemble and they didn’t mate perfectly, so I decided to drill the connecting flaps at strategic points & secured them together with stainless steel screws and dribbled some liquid flux under the flaps.

I “cooked” the whole thing on a hot plate. The plate was turned on full blast (over 300C on my IR thermometer). I fed fluxed solder into & into the joins & then let it cool. It went reasonably well. I got only one small dribble inside and there are only a couple of cracks between waveguide & horn where the two pieces didn’t quite mate. I doesn’t look as professional as Brian’s effort, but I was quite pleased with it for my first attempt at a horn. It looks like it should do something.

G3YJR_6cm_horn

3-April-2018 update: I tried using my biggest soldering iron to fix the holes, but it didn’t work, so I bashed the cracks closed as best I could and then cooked the horn on the hot plate again & soldered over the cracks. At the same time I soldered in an SMA socket with a long protruding pin. The pin is about 12 to 13mm long, so I’ve left it untrimmed. I’ll try it as it is. I removed the temporary screws, so there are a few little holes through the horn now. I hope they won’t matter.

I bought a little box (a Toolstation “moulded enclosure”) which I hope will house the horn & the transmit & receive modules along with a sequencer & a relay in order to make a transceiver which will take the weather. Maybe it could go on the dish? I will need to feed & receive video, audio, DC & PTT. A monitor line would be useful. Remote channel control might be fiddly.

6cm_ATV_box

Perhaps the microwaves will pass straight through the plastic case & grommets? We’ll see!