Tuesday, January 18, 2011

KPA100 Completed!!

I haven't posted here for a while, but I have taken a few pictures along the way. Now that the project is done, I thought I would catch up here.

Here's a look at the KPA100 board after the last component had been stuffed, and before mounting it on the heat sink/K2 cover. I put the big 800° tip, the one I use to assemble dipole antennas made out of #14 wire, on my Weller to solder the power transistors to the board. That did the trick very handily.
When assembling T1 and T2, I scouted around the Web looking for pictures. I found some which were helpful, but I decided to take the pictures I wish I had found. This one shows the detail of how T1 was soldered to the board.
Here is a detail of T2's installation, showing both how it is soldered to the board and, in particular, how C83 is mounted on T2's metal frame.
Here is the final alignment and test setup. All procedures in this section of the manual went fine. I made one contact on 40 meters in this configuration. It also became immediately clear as I tested transmitting on the various bands that the KPA100 is quite sensitive to SWR. At this point, I reconfigured my good old Heathkit antenna tuner, which I had just been using to tune my 80/40 meter random antenna, to now tune all my dipoles as well. With SWR now 1.0 to 1 on all bands, the KPA100 happily ran at 100 watts with no power reduction.
Here is the completed K2/100, with the antenna tuner now located in a more convenient place. I made a couple of contacts on 30 meters (HB9 and F5) and ran upstairs to get the camera!

So, I'm at the end of my Elecraft kit construction, for a while anyway. I'll see how the ARRL CW DX contest goes next month, and maybe look into building the KAF2 later this year.

I did not enjoy building the KPA100 to the same extent that I did the K2 and mini-modules. I found it to be fairly grueling, but I'm not sure why; maybe I just needed a longer break before starting construction, or maybe I needed to do it without the February contest staring me in the face. However, the KPA100 works fine "out of the box", and demonstrates again that Elecraft manuals are first rate; you just need to follow the instructions carefully (and especially so when an instruction is in bold font).

Constructing the power cable was a nightmare. Fortunately, this posting to the Elecraft K2 list provided some really helpful hints, especially about installing the fuse connector; I don't think I could have done it without Jay's suggestions. If I were to do this again, I'd buy the pre-assembled cable from Elecraft.

I'd suggest one change to the K2 build that would make KPA100 integration easier, and that is I would include P3 and P6 (RF and power connectors) on the K2's main board as part of the standard K2 build. I don't know what the statistics are on how many K2 builders go on to build the KPA100, but it sure was a nuisance having to disassemble and re-assemble the K2's heat sink to mount these two parts. I would have much preferred to install them as part of K2 construction.

There were no problems with clearance of all those capacitors on the bottom of the board; they all cleared the back of the heat sink with ample margins.

Two surprises: while doing the inventory back at the beginning, I discovered that KPA100 provides a DB9 serial port, allowing the K2 to talk to my computer. I built the serial cable last night and, sure enough, CTWIN can change bands on the K2! The other surprise came up fairly late in construction, and that is that KPA100 provides an on-board SWR bridge and metering. So, my recently built W1 is now off-line. However, I was still glad I built it, since I used it to calibrate the power and SWR metering on the KPA100; it was very handy reading exact power and SWR measurements on my PC!

Thanks to the parts and support folks at Elecraft for their fine help during construction. And thanks as well to Don, W3FPR, for his friendly and very informative support.