Category: Electronics

MFJ-208 refurb project

An examination of the innards of the MFJ-208 antenna analyzer didn’t reveal any obvious problems other than the messed up variable plate capacitor.

Everything else inside looks pretty clean.

With a pair of needle nose pliers and some very gentle pressure, I was able to bend the plates of the variable capacitor back to where I thought they should be. Both plates are parallel to each other now and don’t hit each other when rotated.

Now I just need to put everything back together, add power and test it out.

MFJ-207 refurb project

Spent some time going over the innards of the MFJ-207 antenna analyzer I picked up and doing some research to figure out what kind of rotary switch I’ll need to replace the existing messed up one with. I think I’ve found the correct replacement switch (a Lorlin CK1025 rotary switch).

Everything else inside looks in decent shape as far as I can tell. I haven’t tried to test all the individual components yet. No leaky/bulgy capacitors or burn marks and all the soldered connections seem solid. Aside from the rotary switch I’m not seeing anything else wrong with it.

Now to go over the MFJ-208. I don’t know if I’ll be able to find a variable plate capacitor to replace the existing one, but I might be able to fix it up so that it works the way it should.

Refurbishing antenna analyzers

While browsing radios on ebay, I came across a couple of MFJ antenna analyzers: an MFJ-207 and MFJ-208.

They were both being sold as “For parts” and the person selling them wasn’t able to test them. From the description and the pictures that were posted, my expectations weren’t very high. The price was pretty low, and I figured if they worked I’d have a couple of antenna analyzers for pretty cheap and if they didn’t, I’d have an interesting project on my hands that I could learn something from.

They arrived in the mail today and I had a quick look inside both of them. Off the bat the 207 is going to need a new band selector dial. It looks like it’s supposed to be a one of those multi-position switch knobs, but if it was it isn’t anymore. On the 208 it looks like a new variable plate capacitor is in order. I’m no expert but I’m pretty sure the plates aren’t supposed to touch when the knob is turned. I’ve also never seen a variable plate capacitor with just two plates (one moving, one stationary).

I’ll have to spend more time and go over them more closely, but if these two things are all that’s wrong with the two analyzers, then this should be a pretty easy refurb project for me (provided I can find the parts). Fortunately the manuals for both of them are available on the MFJ website, and the 207 manual even has a schematic in it.

This should be interesting. Pictures to follow

Adventures in electronics

Finally found some time to sit down with all the bits and assemble a second Morse code key using the supplied schematic. At first it didn’t seem to work, but after checking through everything I found one of the speaker wires wasn’t fully inserted (short lead). After I fixed that, it buzzed at me when I clicked the button! The button is the clicky kind, so it’s not that well suited for doing Morse code, but it works! The buzzer was also a lot louder than the kit, which I later discovered was due to me forgetting a resistor between the final capacitor and speaker.

The next step was to make it light up in addition to buzzing. Spent some time looking at the schematic for a place to insert an LED that I didn’t think would make it go poof or fry anything. Put in a red LED and connected it to ground, pushed the button and it lit up! Then I decided to try a second green LED in series with the red, and they both lit up! Success!

A variable resistor instead of the fixed resistor in front of the speaker I think should give me some volume control, so I’ll try that next. I need to get one first.