AB4UG Radioblog

Review: MFJ-1906HD telescoping mast

Ordered an MFJ-1906 fiberglass mast from DX Engineering over the weekend and it arrived at the house yesterday.

I ordered the 33′ hose clamp version of the mast, but what ended up at the house was the 38′ quick clamp version (MFJ-1906HD). Even the label on box said it was the hose clamp version. Factory labeling error I guess. Can’t really fault DX Engineering for sending the wrong item.

Instead of the expected six 6′ sections of fiberglass tubing inside the box, there were seven 6′ fiberglass tubes along with 6 quick clamps. It’s a pretty compact package. One 6′ x 2.5″ OD tube with all the others nested inside.

The quick clamps need to be glued to each mast segment so that they don’t come off while you’re extending each segment. The only suitable glue I had was epoxy, so I just used that.

Final assembly is just a matter of adjusting the quick clamps so that the tubes slide into each other and holds securely when the clamp lever is in the down position. I marked the bottom end of each tube at 12 cm (the instructions suggest marking them at 1 ft (~30 cm) as an indicator to stop pulling each tube out.

Final length is just over 2.1 m (7′) and fully extended (leaving about 12 cm nested inside the previous segment) the mast is about 12.2 m (40′) long. Leaving about 30 cm nested in each segment would bring the total length down to just over 11 m (37′), which is still plenty long enough for my purposes. Probably a good idea to leave the thinnest tube nested a little further inside for extra strength, especially on a breezy day.

The mast seems pretty sturdy, although I can tell that getting it up is going to be at least a two person job. At somewhere around 10 kg (~20ish lbs), the mast doesn’t weight a whole lot, but the length can make it bulky and unwieldy. The quick clamps should easily hold each segment well enough for the mast to support a wire or other light weight antenna.

The quick clamps seem like they’ll need readjusting, especially if they’re being locked/unlocked frequently. Don’t drag it on the ground while you’re carrying it around, especially on hard surfaces or you’ll end up grinding away the mast.

Now to figure out how to secure the dipole to the top of the mast.

8/10 stars. (10/10 for value in my case).

Power supply: Updated schematic

I’ve updated the schematic for the power supply. Made a few corrections and rearranged a few things.

Still haven’t figured out why the outputs are behaving like they’re shorted out. Putting a my DMM across the output terminals gives me about 148Ω, which seemed on the low side to me.

A quick check of the SCR shows that it seems to be ok. I think I’ll check the pass transistors next. Looks like they should be easy enough to remove for a quick test. I should probably check the big filter caps too, although I wouldn’t expect those to be bad.

In the process of troubleshooting, I’ve removed the 6 pin connector and large capacitor (1.4 mF) associated with it. I’m planning on replacing them with Powerpole connectors. Three of them will fit nicely in the space occupied by the 6 pin connector. Just need to figure out how to secure them in place.

CARS President-elect

So I’m now the President-elect of the Charleston Amateur Radio Society.

The nominating committee put forth their selections for the club officers at the June meeting, and at the last meeting this past Monday, people at the meeting voted for them. Since nobody else stepped forward to throw their hat into the ring, the officers selected by the nominating committee were all elected by acclamation. Of the officer positions, the only new person was the President (me).

I’ll start my new job with the August meeting. It’s a bit of a higher profile position than I’m used to taking, but I’m looking forward to serving the club as President as the club heads towards its 50th anniversary in a few years.

Power supply: It lives!

The power supply lives!

On my initial inspection of the power supply, the only obvious thing wrong that I had found was a blown fuse. After replacing the power cord, I noticed the power on lamp had burned out too.

Off I went to the last remaining Radio Shack in my area (a franchise store, also known as Hurricane Electronics) to see if I could find some fuses and a replacement lamp. Found some replacement fuses easily enough (35V, 20A), and much to my surprise, replacement bulbs that were the exact same style as what was already on the power supply.

Replacing the light was easy enough, but took a bit longer than expected. The original pair of wires for the light kept breaking when I tried to put the light back into place, so I ended up just replacing the two wires with some 18 gauge stranded wire I had. Once the light was back in place, I plugged the power supply in and on came the light. Yay!

Then I replaced the fuse, turned it back on and was greeted with the meter telling me there was 13ish volts. With my DMM, I read 13.3 V DC at the meter.

I tweaked the pot at the control board to bring it up to 13.7 V DC.

So it looks like the only problem with the power supply was the blown fuse. Now to see how it works with a load applied.

Power supply: Power plug replacement

With the power supply schematic mostly done (I need to make another pass through to check that I got everything right), I decided the power supply needed a new input plug.

The power supply came with a two prong plug and a smaller two prong socket for power input. At some point someone had soldered a regular two prong power cord to the plug, which I quickly removed (mostly to get it out of the way).

The smaller socket (the round one on the right in the image below) looked like it might have been something standard decades ago, but didn’t look like anything I recognized.

The plug and socket both came out, and I dug out an old three prong power cord from the junk box. After spending some time figuring out how to connect things, I wired in the power cord.

Inside I used a terminal block to connect the power cord with the wires that used to run from the original plug.

Ground on the power cord got tied to the chassis, while the neutral line went straight to the transformer, and the hot line to the power switch.

Plugging it in and pushing the power switch made the transformer produce the characteristic buzzing sound, but it looks like the power indicator lamp is burned out. 23.2 V AC measured on the output of the transformer, which seemed reasonable. No smoke released, which is a good sign.

Now that I can get power into the power supply, I can start figuring out what works and what doesn’t.