Sunday, September 30, 2012

RockMite 30 Arrives and the Build Begins

The 30 meter RockMite kit finally arrived in the post and this weekend I will begin the build and then complete my RockMite trilogy!
The intention is to incorporate all the mods I have used on the 40 and 20 RMs, adding the more powerful 2N3053 transistor, reducing the resistor R18 to a lower value and altering the zener diode D5. I will also soften the sidetone with Dave Benson's recommendation of a "10 10" filter (10 ohm resistor and 10uf capacitor)
Then on top of that I will add the bifilar PA mod (toroid) and include the CW audio filter I built earlier. Add sockets to the components I may want to change, which will include the crystals as the frequency I will be using is 10.116 instead of 10.106, (I’ve done some research here and 116 looks a little friendlier for my slower CW)! I managed to pick these up from the same company who sold me the audio filter, the Hamshop. It's a good shop for buying those sort of parts that are sometimes hard to come by.
Finally I’m changing the enclosure to an aluminium case which will be slightly bigger to take the audio filter and also so should I wish add extra components in and outside the case such as LEDs switches etc. So, in all I should have a nice little RM transceiver complete with all the mods and an output of around 700 milliwatts.
I’m also very tempted since 30 meters is my favourite band, to purchase the small amplifier from QRP project a German company that has some very good reviews. Getting the power up to approx 10 watts just for the one transceiver might prove fun especially on 30 meters.  
The other project I’d like to go ahead with is to buy the OHR 100A 5 watt CW transceiver from Oak Hills Research. I’ve been eying this little kit up for some time and believe it will be ideal for me to progress in my QRP kit building quest but we’ll wait and see how I am after the completion of the final RockMite build. 

So on with the build:
The first procedure for the RM30 mods is to cut some of the traces between various components, I thought I would do this first while the PCB is free spaced giving me more room to work.

So my first trace cut was for the sidetone filter which was between pin 5 on U3 and C8 which you can see top right. The next cut was for the PA toroid mod which again on the bottom of the PCB is a cut between L1 and C14 (middle left of the PCB) a bit tricky as it's fairly close together.

Turning over to the top of the PCB and continuing the trace cuts for the PA mod I cut a gap at both ends of the trace between L1 and C1 (middle right, a bit small but the picture will enlarge).

With all trace cuts completed I will now start fitting some components and sockets. I will also fit the PA mod toroid by inserting the jumper lead between C1 to the junction of C14 C15 and L2 and solder up the centre tap of the toroid (ab) in to L1 and then a and b taps in to the holes either side. Below is the details of the toroid fairly simple but a first for me!

Two hours later and the majority of the PCB build is complete with the toroid in place, which was a little fiddly to fit but I finally got there in the end. All I have to do now is insert the sockets and add the 2N3053 transistor together with the lower value R18 and the 10.116 crystals. Finally to finish off before the smoke test add the "10 10" filter on to the bottom of the PCB.

I'm pretty pleased so far, my soldering has certainly improved since first starting a few months back on the old RM40, just proves practice makes perfect! 

 The "10 10" filter for the sidetone mod and the jumper to complete the PA toroid mod.

Nearly there, the completed RM slotted in to the enclosure case, you'll note there is plenty of space left as I want to add the CW filter and internal batteries. I've also added an LED and an off on switch just to make things easier.

 The internals look fairly neat for even to me! I've fitted sockets to the transistor (which is not in the picture), and for the crystals, hence the copper ring which acts as ground and can be opened up when I want to replace each crystal.

And finally all sealed up in the lovely new enclosure! I will add some small black decals so that I remember what everything does. So far no successful QSO but to be honest I haven't really given it a proper try, although my Brother-in-Law down the road, (about 4 miles away) could hear me testing when he was listening out on his FT1000D, so I am getting out at approx 700Mw, I will attempt a proper try later this week, so hopefully the next post will bring some good news!

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