Tuesday, 6 August 2013

MTR version2

I was lucky enough to secure another MTR (Mountain Top'er) kit from Steven Weber, this from his second batch released at the end of March 2013. I had been keeping an eagle eye on the AT Sprint Yahoo group for news of the release of another 149 MTR kits. I was amazed when an email came through just as I was getting up for work early one morning announcing that orders were being taken for the new run of MTRs. I ordered straight away but I was worried that I might have missed my chance to own another MTR as I worked out that it had taken 40 minutes for the original email to come through to my phone. I need not have worried though as I later learned that only twelve kits had been spoken for by the time I ordered.

My order confirmation came through pretty quickly from Steve, I was over the moon to have secured another MTR, this time with a neat custom case. The package arrived around 2 weeks after ordering, Steve stated that he had bought the entire stock of shipping boxes from his local Post Office and did not have enough to send out all the orders! My kit had been held back a while whilst Steve sourced some more boxes.

The kit was neatly sealed in plastic and the components were grouped together to make finding them a bit easier. Thankfully all the components were there with none missing. I think Steve does a great job with his kitting, it must be a nightmare with so many tiny components to count out. There were 149 kits made available this time around and just as with the last run, each kit was given a unique serial number, my kit being #267. The numbers for the second run started at #151, as they followed on from the last number of the first run kits.

 The board went together well, although it was time consuming; there are more components than you realise and you have to build on both sides of the board. The processor and DDS chips were mounted first of all and I had learnt from my experience with my first MTR, so this time the chips went on pretty smoothly. I followed the assembly sequence suggested by Steven, KD1JV.

 The build instructions had a few small mistakes, mostly due to the fact that the manual had been modified from the one for the first run kits. It didn't take much thinking to work things out though, the provided schematic helped out here. The obligatory PCB trace error had crept into the design just for a bit of interest,  so a small wire jumper from Q2 (top left) was needed. The ground pad for the antenna connector also needed modifying, it had been flagged as a via by mistake so the solder resist had to be scraped off with a sharp knife.The smoke test went well and soon I was ready to fit the final inductor (L14) for the PA and perform the alignment. The alignment firstly consists of putting the rig into calibration mode by powering up the board whilst pressing two front panel buttons. The rig then sets up a 10MHz signal from the DDS, this signal is measured using a frequency counter at the provided test point. Using the up and down buttons, the signal is calibrated to exactly 10MHz.

Once the reference oscillator is set, the BFO needs to adjusted, this is simply a case of measuring the audio output with an oscillscope and peaking the internally generated audio tone for maximum amplitude using a single trimmer capacitor (CT1).

All that is needed to be done after calibration and setting of the BFO is the align the RX band trimmers. I used my FT817 (my only commercial HF rig) to provide a signal to tune my SOTA dipole using a manual ATU. I tuned for 1:1 VSWR  at the radio and then swapped the FT817 for the MTR and peaked the two trimmers for the first band for maximum response. I then repeated the whole operation again for the second band.

The board had already been tried into the case in order to cut the wires to the correct length for attaching to the external sockets. Putting the PCB into the case was just a matter of disconnecting the power and antenna jacks, as these pass through the case from the outside, and then resoldering them when in the final positions. The board is held in place by  four screws through the top of the case and into the stand offs soldered into the PCB at each corner - a neat solution. A strip of felt across the four push buttons gives a tidy appearance along with the red transparent plastic window for the display.

The rig is very pleasing to use, I built my second MTR for 20m and 30m, and I find 30m is great for weekend SOTA when there is also a big contest on the bands. I like the new case, but I probably prefer my original Altoids tin MTR, it's so much more compact and lighter too! My Altoids tin MTR weighs in at 80g, whilst my new MTR with it's pretty case weighs in at 170g! There are some minor circuit board changes to the second run kits and it might be all in the mind but i find I prefer the audio of my first run MTR.

KD1JV has produced a great little kit that works very well. I'm sure these MTR's will be sought after for years to come. There are apparently 299 MTRs out in the wild and it's unclear whether there will be any more produced, Steven was making noises about making a more complex rig next time including DSP.

1% of the world's population of MTRs!