Yearly Archives: 2017

Construction, Ham Radio

Machining Heatsinks for QRO Amplifiers

Back at the 2012 Friedrichshafen Hamfest I brought a 1.25 kiloWatt VHF amplifier kit for 144 MHz from F1JRD and F5CYS. These devices were fairly new at the time. It took me a year to pluck up the courage to build the pallet, but I went about it all wrong. With the help of Dad and the kitchen hob, we soldered the jrd1 Teflon PCB to the C110 copper heat-spreader as suggested in the Dubus article (see here). I had the pallet working at the time, giving around 600W of RF, which was about the maximum my 1000W 50V PSU was capable of sustaining. When I came to boxing the device up into an amplifier to use with EME and Meteor Scatter in late 2016, the part failed under test.

After much deliberation, I have ordered parts to repair the amplifier project. I found Jim W6PQL‘s website (see here) a wealth of information, and Jim also offers to supply parts and designs to help others. I ordered a set of PCBs to replace the original jrd1 board, a NXP/Ampleon BLF188XR 1400W part to replace the failed the Freescale/NXP MRFE6VP61K25H 1250W part, and some other accessories that Jim sells. The parts were posted by Jim today, so I decided it was time to recover parts from the old PCB and recondition the heatsink and heat-spreader.

The first step was to remove the jrd1 board from the copper heat-spreader. I used the kitchen hob to heat the copper heat-spreader, since the old board was soldered to the copper block. The board damage was sustained to enable the removal of the more expensive components.

Below, the heat-spreader with the jrd1 board removed. I used a solder sucker and scraper to remove as much of the molten solder.

Once the heat-spreader had cooled down, I mounted the copper spreader up in the milling machine read to re-machine the top and bottom surfaces. Great care was taken to level the block using parallels. Below you can see the fly-cutting process on the first cut, removing just 0.05mm from the surface.

With the top and bottom of the head-spreader machined flat, a small end-mill cutter was used to machine the transistor slot to the correct depth following the skimming of the top surface. Then the heatsink mating surface was machined. Below you see the first cut on the heatsink.

The finished parts. A few machining marks, but the surfaces are perfectly good enough. Some dents on the copper block, but it’s not worth removing all of the material to eliminate these.  Using a few drips of water as a substitute for thermal compound, the two mating surfaces stick together very well (with a good vacuum forming). That’s more than good enough for my needs!

Now I just need to wait for the parts to arrive before I can finalise the PCB and transistor mounting! This story continues here: Soldering Expensive Transistors.

Ham Radio, Rally

Rosmalen Hamfest 2017

This weekend I drove to the 42nd Dutch National Radio Fleamarket hosted by the Bossche Radio Amateur Club and held in Rosmalen at the Autotron, Graafsebaan 133, 5284 The Netherlands.

This year, Dave G7UVW couldn’t make the trip, so Dave M0MBD jumped in at the last moment. In total, five of us were crammed in my car: Chris G8OCV, Peter G0IAP, Dave M0TAZ and Dave M0MBD and myself, M1GEO. Dave M0TAZ drove Peter G0IAP and Dave M0MBD from London to my home in south Norfolk. And from there we all headed to the Harwich International Ferry Port for our sailing at 23:00 to the Hook of Holland (courtesy of StenaLine). We always aim to arrive at the ferry early, put our luggage in our cabins, and then head to the bar for discussion and drinks!

In the morning, an all you can eat buffet starts the day well. The Rosmalen Autotron conference centre is about 50 minutes by car from the Hoek Van Holland port. After paying the entrance fee (€8, 2017) we were free to roam around from about 9am till 3pm when the conference centre closes.

As well as providing a great chance to purchase some parts for constructing projects, the hamfest also provides a good opportunity to catch up with friends from around western Europe. It was good to catch up with Niels PA1DSP and Pieter PA3FWM (of WebSDR fame), among many others.

Returning to the ferry terminal, we had a short wait before the check-in opened. We passed this time in the terminal building, using the remaining few Euro coins to buy coffee from the vending machine. Once we had boarded the ferry we offloaded our cases into our cabins once again and convened at the bar for a drink before our 3-course evening meal.

Another breakfast starts off the Sunday morning well. Departing the ferry at about 7am allows you to get home early and still have most of the day to yourself, to enjoy your hamfest purchases! All in all, the total cost of this year’s trip was £158 per person, including all food and fuel. Not too bad at all!