I’ve always wondered why my FT-450 I bought second hand had a lower RX level on the higher bands, starting around the 20m band. I took a look at the schematic, and the input on the RX side is very classic: a DC blocking cap and protection diodes.

Protection diodes, wait – those aren’t RF protection diodes; they are bog standard SMD red LED’s! What was Yaesu thinking here? (“Let’s save 2 cents?”). Only reason they might have used these (and the only reason I can think of) – is that they maybe have a low capacitance. But seriously, Yaesu.. ?

Anyway, I set my multimeter to the diode setting and quickly realized that one of them was shorted. Really, who tries to use LED’s as protection diodes? Really not up to the task. Here’s one that was still working. The picture gives a good indication where you can find them on the PCB (underside of the transceiver).

So I’ve been messing around with SMD component level repair and building for some time, but for more complex boards with things other than discrete components – a regular hot air station just doesn’t cut it. Also when working with 0402 or smaller, they just get blown away. The solution to all of this, is to get a reflow oven. The bad part? Expensive. The solution? DIY! I did some research and there are some things you need to look out for: Ideally; you want quartz heaters – as these have low thermal mass, you’re able to switch them fast The smaller, the better (well, in relevance to Wattage).

So I acquired a SEA 1612C remote ATU for cheap, but without an enclosure. I figured I’d buy my own enclosure anyway, so no big deal.

As I didn’t want to use any remote cable at all, I had a little challenge:

• I need to give it power. Okay, that can be done via a bias-tee. The tuner isn’t made for it, but can be modified.
• I need some way to be able to “tune-on-demand”. I settled on a small Arduino Nano, but will eventually do this via a ESP8266 (I can remote control it via WiFi then)

So what is a bias tee? It’s actually no more than a handful of components: a couple capacitors, some ferrite to make a choke, and some nuts, bolts, sockets.. and a fuse. You double up these components to make one for the other side as well.

So what’s it look like? Well, see below. C1 in my case is 2x 10nF – 3kV capacitors (in parallel – so 20nF in total). F1 is a Ferroxcube 4C65 ferrite, wound with about 30 turn of magnet wire. It makes a nice 3-30MHz choke when testing it with a Vector Network Analyzer. F2 is a 3A fuse.