Nothing happening?

No posts for 12 days! What's going on?

My plan was to get the front and rear panels cut by now but various things have got in the way, not least the fact that it is very cold in my garage and working indoors just seems to be more appealing. However, I have not been entirely idle...

I decided that I would invest in a bench drill (drill press to our American friends) as a prerequisite to drilling the large holes for the fans. While investigating how best to mount it, I decided that the old bench was in need of repair. It was built by my father, some time in the 1960s, using Handy Angle. UK readers of a certain age may well remember Handy Angle, slotted angle about 40mm a side, made from a strong aluminium alloy. The nearest thing to it these days is probably Dexion but I think that is only made in steel. 

Anyway, the wooden work top, which I replaced perhaps 30 years ago was very much on its last legs after a few decades of sawing and drilling and generally bashing bits of metalwork. As luck would have it, I have recently had a new kitchen fitted and the very substantial tall cabinet end panels from the old kitchen cabinets would make an excellent worktop so that became the cunning plan. The panel is almost exactly the right length, 2140mm but at 600mm wide it is about 100mm deeper than the original workbench. 

I thought it would be better to deepen the work bench rather than attempt to cut down the panel, so some more aluminium angle to extend the frame was needed. Of course Handy Angle is no longer available but in this case ordinary 40mm x 40mm x 3mm angle will do the job perfectly well - just drill M6 holes as needed, I ordered the necessary materials cut to length from Aluminium Warehouse a few days ago and they have just arrived as I am writing this missive, so I have work to do! I have a nice new vice (vise) and the aforementioned bench drill ready to go, once I finish the workbench. 

Meanwhile, in the warmth of the shack, I have added a fair amount of new code to the controller and tidied up the wiring somewhat. Having now fixed the problem with correctly measuring heatsink temperature I've also been able to complete the temperature sensor and fan control logic, so the fans only come on to the extent that they are needed.

The control touchscreen layout has also received some attention, with various options such as variable brightness and beep level added to a nascent "settings" page. I expect more stuff to be added to that page in due course. There is now a timer which counts the number of seconds that the amplifier has been in Operate mode (50V supply on) and the number of PTT seconds (actually transmitting). It'll be interesting to see what the ratio is but I am guessing less than 20% TX time in normal use.

Well, I suppose I had better go and brave the Cumbrian chill (3°C as I type this) and get that workbench finished.

Some practical experience

It was time to get on the air. A convenient UKAC 2m contest was later in the day and first hand experience had shown that 100W really does not cut it from IO84. It nearly didn't happen because of storm Barra, which raced across 'WGV-land at a rate of knots during the afternoon, forcing me to luff my tower over. As the 8pm start time approached thing seemed to be calming down, so I decided to risk raising the tower and give it a try.

Yes, definitely an improvement. Conditions were pretty flat but QSOs were easier to come by and with less waiting around while all the other stronger stations made it ahead of me. A total of 25 QSOs was a bit better than I have managed in the past but importantly almost everyone I called I was able to make a QSO with and I even got a few replies to my CQs that hasn't really happened before.

A few minor problems emerged. The lash-up arrangement meant that RF was getting into places it shouldn't, making monitoring of power output and SWR difficult. I already knew that I would have to write software to perform peak hold/slow decay functions on the various meters and the contest proved that emphatically.

Post contest I have spent some time on the peak hold/decay software and that is now more or less working. I've probably reached the point at which I need to put more effort into the hardware, completing the front and rear panels and getting the amplifier into its case. Why do I always end up doing these projects in mid winter when the garage is more appropriately a place for the car to live in rather than a freezing cold workshop? 

Generally the software is now usable but working on that is a lot more warm and comfortable so no doubt that will continue. I know I have to fix some RF ingress issues and the heatsink temperature monitor is not reading correctly but those are (probably) minor issues.

Drilling big holes for fans is next I think.

It works!

With the metalwork more or less completed, the PCB to hand and the software coming along nicely it was time to connect it all up and see what happened.

There is some serious electrical energy lurking around in this sort of kit, capable of making big (expensive!) bangs, so I wanted to carefully test out each stage as I went along. First up was checking that the power control logic was working OK, both hardware and software. As is the way with these things that showed up a couple of minor problems, or design mistakes as they are more properly known. A bit of hacking at tracks on the PCB soon fixed the problem that the PSU on/off control was working the wrong way round - on when it was supposed to be off. Note to self - you need the normally open contacts on the relay, not the normally closed ones... eejit! 

More and more components were added to the PCB as more functions were completed. The fan control software and associated circuitry turned out to be more of a challenge than it rightly should have been due to me forgetting which way up PNP transistors go. Once upon a time I understood all this stuff but I suppose I have been a software geek for too long now and I'm getting rusty on some of the electronics basics. Anyway, it's working now.

Eventually the PCB was fully populated and all tests completed. It was time to apply power to the amplifier. Scary stuff... mistakes could be expensive. In fact it was a complete non-event: the 50V and bias LEDs lit up and that was that. The RF side followed, with changeover relays , a 10dB pad on the amplifier input and the various coaxial cables to be connected. 

The amplifier lash-up ready for testing... wires everywhere!

An initial test with 10W output from the IC9700 (1W input to the amp) showed that the amp was producing about 150W output - an excellent result. Unfortunately, and to be expected, RF was now getting places it should not and it was time to apply ferrite rings/sleeves to the sensor lines to stop them jumping about, which seemed to do the trick.

Increasing input power easily pushed the output to our legal maximum of 400W without further incident. That's despite the fact that the amplifier is not in its case and has little of the screening that the completed unit will have. It seems to be a very stable set-up.

It was time to go on the air! Many thanks to Stuart, G4JHV for a useful series of tests, which suggest that all is well and the amplifier is not producing nasty sprogs or unreasonable splatter. Stuart is just 10km away and we had our beams pointing at each other, so this was a very harsh test indeed. Stuart was running low power but was pinning the IC9700 S-meter at the end stop.

So I seem to have a working amp, albeit something of a lash up for now. I plan to give it a more lengthy test in tomorrow evening's 2M UKAC contest and then, if all still seems to be looking good it will be time to complete the metalwork (holes for the fans, etc.), tidy up the internal hardware/wiring and get the amp in its box.

We're not done, of course! There is still a fair bit of software work to do and, as my software projects never really finish, that will be something of an ongoing challenge. I also need to calibrate the power output and SWR indications and to do that properly I shall need to find a suitable calibrated power meter. 

All in all a good day!

Progress!

Front view

At last the metalwork has arrived, as have the PCBs which came from Hong Kong in less time that the metalwork took to get here from just down the road. Can't help but think that there's a message in there about attitudes to service.

A few other less critical odds and ends have also turned up, so it's time to get down to work. 

Laying out the major components and screening metalwork was first on the agenda.This is where you find out whether it'll all fit and can be made tidy/easy to work on. So far so good - I would not want the enclosure to be any smaller though.

Rear view

Although I had the exact dimensions of the PCB, having it actually to hand made it much easier to visualise how it would fit in. It sits on stand-
offs over the top of a small 12V SMPSU, which will be on at all times unless the rear mains switch on the IEC connector is turned off. Its quiescent power consumption is under 1W so I think I can afford for it to stay on 24x7.

The amplifier section is completely shielded from neighbouring components, including a detachable lid. All coaxial cabling, the changeover relays and cooling fans are all fully contained in this section. 50VDC and the various control/sensor connections are all via 1000pF feed-through capacitors. This should keep the RF where it's meant to be but it will also help with the amplifier cooling by creating an effective wind tunnel front to back.

Amplifier screening lid in place

I still have to cut the front and rear panels. The front panel is just a pair of 100mm diameter holes for the amplifier and PSU fans to pull in air. 

The rear panel also has the two 100mm diameter holes but in addition there will be various connectors: Transceiver in/antenna out coaxials, mains power, PTT input, remote control head output and a micro-USB socket. 

Now that the major components are all fixed in place it will be straightforward to position these items, then another metal bashing session in the garage beckons. Not just yet though... it's pretty cold out there and I am going to warm up doing some inside work for now.

Right, enough of this bloggery... where's my soldering iron?