SHF UKAC 28-Nov-2017

I operated on 13cm & 3cm.

On 3cm, 3W was going into the circular waveguide. I haven’t soldered the waveguide together yet, but at the moment it is holding together with the different fittings just pushed together and electrical tape around the joints.

I’m experimenting with tweaking the dish vertically as well as horizontally. The dish had been battered by winds & I was not sure of its azimuth setting. It was about right on GB3FNY, but seemed to need to go a few degrees further northwards to reach Denis G3UVR. After our contact I elevated the dish a couple of degrees & his signal improved. This may just correct lean in the pole or droop in the dish. Denis is hardly line-of-site over the Pennines and as it is mostly peat bog up there, there is little to reflect off. Propagation is mysterious!

On 3cm, I tried listening for myself on Mow Cop SDR, but heard nothing. Gordon G0EWN worked John G3XDY, but I listened for John & heard nothing. I seem to have forgotten to work John on 13cm. My best DX on both bands was Keith G4ODA.

On 13cm, people seemed to struggle to hear me on SSB, so I wonder whether the PTT has stopped working on the 70cm transverter; this feeds the 13cm transverter. Using CW, there didn’t seem to be a problem;  the RF sense would turn on positively using CW.

Update: yes a wire had come adrift from a relay & there was no PTT switching for the 13cm transverter. I fixed it.

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Testing on 3cm

I’ve squashed the electrickery back into the box on the back of the dish. I wish now that I had found a bigger box, but this was the largest outdoor plastic box that I’d found (from Toolstation). I’ve added a strap around the middle of the box to help hold the lid shut & seal the box against the rain. I added another mini box to cover a hole in the lid. I had to make a hole so the the lid didn’t foul the connecting plugs into the 3-3PA. As it is set back from the dish on stainless steel studding, the box acts as quite a good counterweight to the dish & waveguide.

There are a number of issues still to work out, so 3cm is very much a work in progress. the box contains amplification on receive & transmit now. 3W is going into the experimental circular waveguide; a significant improvement on the 250mW before.

In order to reduce the voltage drop on the power supply to the box, I’ve doubled-up the positive and negative wires to take only the positive, and then take the negative return down the coax cable outer.

My sequencer is quite complicated now as it switches the antenna relay, the supplies to the three amplifiers & the PTT to the PAs. The PAs need supply voltage applied so that they can bias themselves ready for PTT switching to transmit slightly later. The pre-amp is turned off when on transmit.

The LNB clamp that I’d hollowed out fell apart, so instead of the bungie cord, I now have the 42mm straight section of the horn held, pressed into a hole in piece of plastic sheet supplied by Barry G8AGN. Thanks Barry! I’m hoping the opening is close to the focus of the dish.

I’ve had a go at getting the pole vertical, securing the base plate better. Previously I’d added 30cm or so of scaffold pole indoors so that the dish clears the chimney pots. It is also cleared by the 2m yagi just above it. I tightened the straight scaffolding coupler in an attempt to stop the dish weather-vaneing in the wind.

The angle of the SMA transition is probably out, so the polarisation is probably a bit wrong.

I’ve had some problems with the DEM 3-3PA which I am using as a driver. It has a couple of instabilities. The main one, with the self-oscillation generating about 1W, is related to the way the pressure is distributed clamping the case & board to the metal base. That one seems to be under control at the moment. The other is much lower level. I can see it tickling the monitor line of the DB6NT transverter which precedes it. I wonder if it is a feature of the amplifier chip? It makes no difference whether the lid is on the box or not. I’ve tried microwave-absorbing rubber & ferrites all over the place & nothing has got rid of it.

The 3-3PA and heatsink get rather hot on transmit, so I may add a fan. It actually draws more current with the PTT on and no RF excitation than with RF excitation. So whether I’m actually transmitting or not, if the PTT is on, then the 3-3PA is getting hot!

The DEM 3-8PA is wonderfully stable. On its larger heatsink, it barely gets warm.

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Wed-8-Nov-2017: Gordon G0EWN came on the air for a test. He beamed SE towards Penny Hill windfarm & I picked him up easily via a reflection. He uses a Travelling Wave Tube (TWT). He could hear me fine.

Also I found that if I beam towards Mow Cop SDR that I can register on the receiver if I angle the dish up a few degrees. This may be because the pole is leaning slightly or perhaps the elevation just helps the beam get over the ridge & trees at Crosspool. It was a weak trace, but it was there. Also I could hear it echoing my signal back to me over the internet. I’ve tried Mow Cop several times with 250mW with no success, but with 3W I got it to work.