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!