QRP Labs 5W CW transciever kit #6

When the weather broke and it decided to be slightly less like a water park and more like Spring I pounced. Seizing the moment I cracked on with my enclosure and took the opportunity to spray my drive, hands and enclosure Ford Vista Phoenix Orange.

I’ve seen a few enclosures made from PCB material in similar colours and really liked it, so as a build taking inspiration from both options I plumped for it. The whole idea of these colour schemes is so that when you’re out in the wilds being /P you don’t accidentally leave your nice tactical black rig laying around and wander off without it. In short, idiot proofing! Four coats later and my can spluttered and gave out, job done. After 24 hours of allowing the paint job to dry gently indoors in the warmth we have this.

At the same time I ran my case decal through my inkjet printer on water slide decal paper and hit it with three layers of spray varnish before giving it 24 hours to cure.

So the next trick was to add the decal sheet to the case

To be honest I’m really pleased with how things are looking but there’s a really good reason why inkjet print jobs and water don’t mix. Despite three decent layers of varnish to seal the ink against the media I suffered a degree of print bleed when the transfer sheet hit the water and when dabbing down after application. As such the finished article isn’t as sharp as it could be but I’m hoping it won’t be that noticeable. I joked earlier about investing in a laser printer and I’m now serious about doing so. The print process is different to inkjet and as such you get a much sharper print, the ink coverage is uniform and deeper (in my opinion) and for this type of application with the correct media you’re not going to suffer leaching. Also for day to day correspondence it gives a much more professional output. In reality something like an HP LaserJet Pro for just over £200 isn’t a bad buy and with all of the connectivity options it supports it’s moving up the list from “would be nice” towards “ought to sort sooner rather than later”. Add to that that inkjet ink is the 8th most expensive liquid on the planet, it’s time to find a different way to spend £80 rather than on refill packs.

Moving on, a 24 hour drying period is needed before I hit the enclosure with a lacquer layer to seal the decal sheet and to protect my paint job.

So with the enclosure completed it was time to package everything up, but before doing so I wanted to prevent anything nasty happening with the rig. One thing that was noted and commented on is that if you use the rig for WSPR (which I do) the duty cycle (time the radio is in effect keyed down and transmitting) of the transmission is 2 minutes from start to end. Even with the power amplifier in the circuit being Class E and very efficient, there’s no such thing as a free lunch and the power transistors tend to get on the hotter side of warm. The suggestion is to add some form of heat sink to them, which is interesting as you haven’t got an awful lot of room to play with!

Now you can get commercial heatsinks for TO-92 packages but they’re not cheap and they require space around them to attach.

You can see that the one of the left is incredibly close to the stand off spacer for the LCD display which makes things a little tight to say the least!

A bit of Google work revealed several nifty DIY solutions, one from instructables and one from Matt’s Tech Pages, which is truly inspired and uses a 6mm ring terminal to do the job.

The snag is I just didn’t have enough space so it was time to improvise. Take one strip of heatsink, attack with a Dremel and you get something like this.

Apply a small amount of Arctic Silver thermal grease and a small ring of heatshrink tubing and you get this.

Objective achieved with no impact on neighbouring components. OK it’s not the biggest heatsink in the world but some heatsink is better than no heatsink, especially if it prevents transistors from burning out. I’m sure there would have been someway of bridging the transistors to the case chassis, bearing in mind its huge and made of metal it would have done the job nicely, but it would have been way too fiddly and there’s no guarantee that it would remain permanently attached.

For completeness I added a simple commercial one to the MOSFET to help keep things cool.

Job done! Next trick was to shoehorn everything into the enclosure. Only one broken wire and a minor dink to my paint job (which is nagging me believe me!) later and everything’s in place.

Check it still works before putting the case back on.

Add a few knobs for the rotary controls

And Roberts your mother’s brother!

I’m really pleased with the finished result and it’s been a fun build. Next trick is to get the QCX on a real antenna and see what the world has to offer it in the way of QSO’s and WSPR work.