Wednesday, 16 December 2015

20m Spitfire Rockmite is joined by 40m FOXX-3

The 40m Foxx-3 - the big red button is the Morse key.
Click to enlarge any image on this page.
Back in July I wrote about the 20m Rockmite I built into a Stewart's mint tin. Well, now it has been joined by a 1W 40m FOXX-3 transceiver, also from Kanga Kits in the UK, but this time we have a steam locomotive on the lid.

The Foxx-3 is a well-known design that has evolved from George GM3OXX's original Foxx into its latest “-3” incarnation, designed by Derek G4GVM.

I won't go into how it works – you can find out more on the Kanga web site.

The build was quite easy – the first thing to do it drill the mint tin for the PCB stand-offs and open up the holes with a needle file. I used the PCB as a template for that.

The build sequence has good documentation, all the stages are in different bags and you can test each stage as you go.

The first stage to build is the audio amplifier with an LM386 and you test that by touching the volume control connection and seeing if it hums – no problem.

The second stage is the keying circuit, which again is easy to check. I opted for the push button Morse key on the board rather than a socket for a Morse key as this is really just a toy for me.

A slight amount of switchover delay is set by the value of a resistor. I stayed with the suggested value and that seemed fine.

The third stage is the sidetone circuit, which once again worked first time.

Stage four is the crystal oscillator and I had an issue here that when I keyed up the TX note was very wobbly. I read elsewhere that this can be normal until you build the final stage to give it a decent load. This turned out to be the case.

Testing testing!
The final stage is the power amplifier and filter, complete with four tiny toroids. Again, not difficult, but make sure you get the coating off the enamel before you finally solder the toroids in. I used a drop of molten solder on the iron to do this and it seemed to work OK.

The final stage was to put the BNC on the board and I had to increase the temperature of the iron for this as it acts as an effective heat sink.

Finally, it was a case of wiring it up to a 12V lithium ion battery, connecting a a 40 OCFD antenna and headphones and seeing if it worked.

The power output was just under 1W so I left it as it was – you can change a resistor to increase/decrease the power level up to 1W maximum.

Well, the RBN picked it up even if no one came back to me.
Using my Icom IC-756 Pro3 I checked where it was transmitting and adjusted the variable capacitor to put it on 7.030MHz. I then transmitted on 7.030MHz on the Pro-3 to adjust the sidetone offset. I found that this had a limited range before the receiver either went deaf at one end of the range or just hummed at the other. I did quite a bit of to-ing and fro-ing until I was happy – you'll see that one of the skimmers logged me on 7.0299MHz as I adjusted it.

I think that once it is set it is best to leave it.

I also found that I needed to use my ATU to avoid AM breakthrough on my W5GI dipole – the 40m Windom was OK. I had been warned about this.

The finished item in a Stewart's mint tin.
A few CQs using the built-in Morse key had me spotted on a few RBN skimmers in Europe. You can see that my reported speed varies from 13-15wpm as it is very hard to be consistent with a push button Morse key! It is also hard to send the highly-accurate Morse needed for skimmers to decode you, so I was pleased to be picked up in the UK, Ireland, Belgium and Germany during the daytime.

The reported 15-20dB SNR means it should be possible to work people with 1W, although no-one has come back to me yet and I haven't heard anyone call CQ who has been spot on my frequency.

The receiver is reasonably lively and you'll hear anyone who can hear you I guess.

The only issues were mechanical – make sure that when you put it in the mint box that you have enough room for the BNC plug to fit. I need to open up the holes on the PCB board by about 0.5mm to allow space for it to be connected. Doh!

I also had to grind down the three controls on the variable resistors to allow the lid to shut properly.

In all then, the Foxx-3 is a great little kit to make and it obviously works. Don't expect Elecraft KX-3 performance though! It only costs £29.95.

I do think that you will work other hams on it though, at least on the 40m version, and my thanks to Dennis at Kanga for selling it. The next project is an Elecraft K1 kit that I bought back in Christmas 2004 and has been living in the loft unassembled ever since. Shame on me!

Incidentally, the tiny zip-up nylon camera cases for sale in Poundland are ideal for storing and carrying mint box radios like the Rockmite and Foxx-3.

1 comment:

  1. Steve,

    FB build.

    It is a great conversation piece operating on a bench or sitting on a beach with a fishing pole etc with the lid open but I found it was easier to operate in odd WX conditions (unless had the KX3) with these to use a BNC chassis @ 90' to the PCB and the other connections and stick them out of the side of the tin, much like the rock mite. That way you do not need to open the cover during operation.

    The push button morse key... as it comes with a mono 3.5mm socket in another tin (I have a pico keyer N0XAS in a mini Altoid tin and swap it from rig to rig) I expect you could use the Kanga keyer too.