T2FD Calculator

I love a good T2FD antenna and have built a good few. There’s a few variations but they all work well and are easy to construct. I’ve been asked a few time about the length and spacing so I made a small Excel sheet to work it all out and provide data for the 3 most popular variations.

Free free to download and use. The sheet is protected to prevent the formulas from getting messed up but if you would like to experiment with alternative formulas then please just contact me for the password. All I require is for my original credit to remain on any derivative works.

M0LMK T2FD Calculator

4:1 BalUn

I’ve been wanting to built a good 4:1 BalUn as part of the never ending project that is my HF antenna system for some time and today, I finally got around to the job. This is a “true” 4:1 Current BalUn that is wound as two separate 1:1 current baluns and then placed together to create the 4:1 ration. Any 4:1 built on a single core that claims to be a current BalUn is lying and is actually a Voltage BalUn! Continue reading “4:1 BalUn”

Ladder Line Surge Suppressor

I usually get static build up on my HF doublet due to sand particles (I live above the beach) in the air so have been thinking about a way to bleed off the static and provide some protection to my TS-590SG. After a little research, I came up with this, a lightning arrestor/static bleed device that provides a permanent path to earth for DC whilst allowing RF to pass and providing protection from nearby lightning strikes. Continue reading “Ladder Line Surge Suppressor”

SGC-230 relay replacement

A common fault on the SGC range of antenna tuners is a reduction in receive performance as they get on in years. This can be attributed to contamination on the relay contacts since SGC stoped using fully sealed relays. Any small condensation inside the tuner makes it’s way into the relays and causes contamination on the contacts as they are hot switched. The best thing to do is to replace all 26 relays with new units…

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SGC-230 Ceramic post replacment

I purchased my trusty SGC-230 Smartuner around 8 years ago as a faulty unit and soon got it back up and running with a new binary counter IC. It’s worked great since then but has always had a cracked ceramic post on the output terminal. It was one of the jobs I wanted to do but I never got around to finding a new post so when I had time to replace it, I never had the part handy. Continue reading “SGC-230 Ceramic post replacment”

TX audio chain

It started as a simple project to construct a switch box so I could use a single microphone with multiple radios in my home shack. It’s ended (although i’m not sure it will ever end!) with more knobs, buttons, switches and flashing lights that the flight deck of a Dreamliner.

I’m still experimenting and will be posting a walk through soon so stay tuned but for now, here’s a little picture…

M0LMK Audio Chain

1:1 BALUN for ladder line

I needed a 1:1 balun to use with my home brew doublet but I needed it to go between the ladder line and the SGC-230 tuner so it needs to have stud terminals on both the input and the output. I took a look around and decided that making one was the best option.

It’s made using 11 turns of figure 8 twin lead on two stacked FT240-43 cores. See the pictures below…

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Icom IC-7200 QRS mod

I’m a keen user of ALE on the HF bands and recently purchased an Icom IC-7200 to use as a dedicated ALE station. I picked the IC-7200 as I liked the form factor, the fact that is is a dedicated HF radio and that it has a built in USB interface. The only problem with using the IC-7200 for ALE use is that the TX bandpass filters are switched in and out using relays as the radio scans through the bands. This causes an annoying “click, click, click” sound when the radio is changing bands and, when scanning at 5 frequencies per second, can put considerable wear on the relays. Luckily, there is a fix for this problem…

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A real “Shack in a box”

We have all seen the black box radios that have attracted the term “shack in a box” but I wanted a real shack in a box.

I have limited space at home and wanted to enjoy a bit of portable operating but didn’t want to spend out on extra equipment for portable use and didn’t want to keep unplugging the HF radio and associated bits. The solution was to build a “go box” or “jump kit” that contained all of the equipment needed for home operation and could also be packed up quickly and used for portable operation.
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