A 140 Watt 2 Meter Amplifier

So I recently bought an untested KLM 10-140BL amp at a hamfest, for $20. I finally got around to testing it today. It’s a 140w linear amp for the 2 meter amateur band, 144-148MHz. It does not have a preamp. It will take 10 watts of drive power and output 140 watts.

KLM Electronics 10-140BL  

The front has just the IN/OUT switch to manually switch the amp in and out, and a lamp to indicate it is operating. It also has a pin on the back for automatic TX switching. It appears that even with the operate switch on, it is still in bypass until there is RF in it. When I transmit, I hear a relay click in the amp, the light comes on, and it outputs power.

The back of the amp

The back has only the antenna ports and the power / PTT connector. It’s a 4 pin Cinch-Jones connector. The top two pins are for the 12v power supply. The bottom left pin is PTT, and the bottom right is GND.


Back of the amp with cables plugged in

I tested this amp with a Kenwood TS-700a, and MFJ 300w dummy load, and an MFJ-945E tuner, for measuring the output. It’s an HF meter so it will not give an accurate reading, but its enough to see if there is any power output.

I did not have the correct power cable, so I had to improvise. I used a T connector from a VHF radio and another flat connector which may or may not have a name.

The radio used for testing

I plugged everything in, put the radio in CW, hit TX, and nothing happened. Then I realized I am stupid and I had one of the radio’s memory channels selected, not the vfo. I fixed that, hit transmit, the light on the amp came on and I heard a relay click.

The TX/RX switching works!

And heres what the power meter looks like:

It works!

It is amplifying! I don’t know if I am getting 140w, but it is definitely more than with no amp! I’ll have to get a power meter and measure the actual output. Note: the SWR is not actually infinite, thats just the meter. It may be slightly higher than 1:1 but since this dummy load is rated to 650MHz it should be good enough.

I now have an excuse to get a big yagi.

My HF antenna

I thought I’d start off by doing a post about my HF antenna. Right now I have a doublet of unmeasured length, estimated to be about 55 feet long and 45-55 feet high. I had a lot of help from Thomas W2XG, who also gave me the wire for it, so thanks!

All it is is two pieces of 12AWG wire of equal length, with some 300 ohm tv twinlead in the middle, and ropes on the end. The ropes are 1/8″ dacron designed for antennas, and are connected at the other end to some trees. The ladder line is probably about 20 to 25ft long and goes down to a balun made by K8EC. The balun has SO-239 connectors, so I have a piece of coax and some ring terminals to connect it to the twinlead. This is temporary, obviously. It will be fixed whenever I remember to and get myself to go look for binding posts. The other end of the balun is connected to some Belden 7733A coax. It’s very low loss, but also thick and has a solid 10AWG center conductor, which makes it very stiff. That is connected to the back of my MFJ-945E tuner, then a 3ft RG-8x jumper connects this to the transceiver.

I have been able to tune it no problem on all bands 80 to 10 meters, excluding 60m because my radio does not have that band. I can get out to western Europe on 80m, but not much farther. 40m performs very well, and I’m getting out all over the world. 20 is even better, I can get all the way to VK6, pretty much my exact antipode, no problem(FT8 at least). I am running only 100w into it.

So far it’s withstood maybe 30mph winds, but we havent had much more than that here since I put it up.

Here it is as seen from the roof, picture is taken with a baofeng: