M0UAW's Blog

I bought a very cheap Yaesu VX1-R dual band handy last year, it's a cute little thing that covers 2 and 70 but unfortunately it came without the battery. No problem, if it works I'll just buy a replacement, simple. But WOW, the FNB-52 battery is *expensive*, more than three times what I paid for the radio and I could not find one in stock anywhere (I have since found them)... I did find out that the battery pack is a standard 14650 Li-Ion cell in a molded plastic case (presumably including a battery management circuit) and a quick search of everyone's favourite tat bazaar eBay found a pack of two for a not expensive £9 so I ordered some and waited. When they arrived I gave them a few hours on charge and then tried one in the handy, it worked but of course it rattles about and runs the risk of being damaged or, worse, exploding if charged incorrectly as the cell isn't 'protected'. Now I do have a charger but it meant I'd have to remove th

A quick update, I needed a heatsink so I found one from an old PC which is more than adequate, weighing in at almost 650 grammes I reckon it should be able to handle the heat. Problem though, it's not flat. Which makes it kind of difficult to mount the board. Now, I could use some standoffs, PCB pillars cut to length but I'm a little light on machine tools to make an accurate job of it and it'd annoy me that it was 'wobbly'. As it happens, I recently bought myself a new toy. A Flashforge 3D printer so this seemed an ideal opportunity to learn to use a CAD program and find out how dimensionally accurate the printer is. It turns out, it's pretty good. And the PLA takes a thread really nicely. So, my Mini PA board now has mounts, I just need to drill and tap some holes in the heatsink.

I mentioned Si5351 chips in the last post, this QCX arrived in a bit of a state, there'd been an issue with the 5V rail which had fried a few chips, the owner had removed the 74ACT00 already (and there was some minor track damage as a result) but wasn't confident he could deal with the Si5351 chip so he was about to scrap the radio. Which seems a bit of a shame for a chip that costs less than £1 but I understand, the chip is tiny and fiddly to rework, it's not a part I'd recommend working with if you've little or no SMD rework experience. I contacted him off list and offered to help, the radio arrived in due course and this is an intermediate progress pic, the Si5351 chip, IC1, removed, prior to flux cleanup. I had to take out C2, R4 and R4 as well as the crystal to be able to get to the tiny MSOP-10 chip, the SOIC-16 FST3253 chip is huge in comparison. After replacement (and removal of the FST3253, it's cheap enough that it's silly not to repla

I've bought a few bits from Hans Summers via his QRP Labs site , low pass filters, an Si5351 synthesizer kit, they've been really nice quality and work as advertised, I highly recommend Hans' kits, they're well thought out, good quality and great fun, Hans is also very helpful and active on the QRPLabs mailing list with tips, suggestions and advice on how to sort out problems people may encounter. But, the mailing list, there are posts on there from people who have had accidents with their QCX or other kits and need repairs that they just don't feel confident or able to do, SMD rework of the FST3253 chip or the more difficult Si5351 chip (which is tiny) seem to be the main stumbling block for most so I've offered assistance to a few people and have built up a small stock of spare parts for the QCX. I usually offer free labour repair for things that interest me because it allows me to get my hands on equipment I wouldn't or can't buy for myself for va

We've all seen switching FETs used as PA devices in HF radios, I've experimented with them a few times, lashing up circuits using IRF520s and, my favourite, the FQP13N10, they can produce some useful power for such a cheap device and if you drive them hard, they give some serious power, at 24 volts, with a shade over 3 watts drive I've measured 45 watts output at 30MHz from a single device into a dummy load (you really don't want to put one on the air like that though, the output was horrible) When you drive them hard, they're fragile, gouts of smoke, chunks of epoxy encapsulation flying across the room and dead fuses are easy to obtain so, I gave up, 'proper' RF devices aren't that much more expensive and are designed for use in radios. So, why am I talking about them again? Well, I bought myself one of the Chinese eBay specials, a Mini PA 70W HF amplifier that uses a pair of IRF520* devices to produce a reputed 70 Watts output. (I've no idea