SOTA with QRPp At-Ti-tude

Activation Reports
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For a bit of a personal amusement I’ve been working on a RockMite transceiver casually over several weeks.

Though there are designs simpler than the RockMite, I was drawn to it because it strikes an ideal balance, delivering surprisingly excellent performance despite its simple, bare-bones circuitry.

My standard RockMite 20 puts out about 330mW from a 12v supply and, in it’s Altoids tin case, weighs 81grams. I wanted to try to cut down some of that weight and get rid of the need of the heavy battery providing the 12v.

I’ve used PP3 batteries in the past, for the LA1KHA challenge, but these weigh in at >30g just by themselves. The USB rechargeable lithium 9v batteries aren’t any better. I decided upon a 350mAh 2S lipo, weighing around 18grams.

I still wanted a useful >300mW output from the RockMite so I modified the circuit with a PA transformer and low pass filter inspired by the ‘P&E mod’ documentation from QRPme. With the mods in place, I’m seeing about 340mW output when powered by the 2S battery.

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During build - tiny PA transformer on FT23-43 core.

To save weight I made a case from 0.3mm titanium sheet, this saved quite a few grams over using an Altoids tin.

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Case from pure titanium

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Even with the battery, the titanium RockMite weighs 6 grams less than the standard RockMite on it’s own (fuse weighs about 1g, optional?).

The radio seemed to work OK on the bench, but there’s only one way to know for sure if it worked and that was to put it on air. Firstly I needed a lightweight antenna. I decided to try an EFHW cut for 20m. At 300mW, I figured that I could get away with a small core for the transformer so I opted to use an FT37-43. The finished antenna weighs in at 54 grams.

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EFHW for 20m with FT37-43 core.

I took the untested rig and antenna combination to Whernside G/NP-004 today to give it a try. I was pretty amazed to be working pile-up style for about 15 minutes! I got 16 QSOs in the log. I hadn’t done Morse since August and I felt that I had landed in the deep end somewhat! I had a weird situation where I was mixing my Ys and Qs, not something that usually bothers me, I was having to think hard about it!

It was a very enjoyable activation despite the cold wind and mist.

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Pico paddle seems a bit big, I have a smaller, lighter keying solution in the works.

Thanks to all the chasers today, you made my day! It never ceases to amaze me just how far a bit of QRPp CW on HF will go.

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73, Colin

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:rofl:

Gordon Bennett! If you make the key any smaller the only folks that will be able to use it are The Borrowers!

Also, I didn’t cop it was a battery at first. I thought it was one of those delicious Refreshers chews.

Great stuff! :+1:

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Apparently chewing on a lipo is quite similar to eating refresher bars, they have the same fizz.

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Yes, a truly fascinating QSO harvest, not least (or only?) thanks to the many active SOTA chasers today. Well done, Colin.

Before the turn of the millennium, i.e., before SOTA, WWFF, POTA, … and Smartphones, something like this wasn’t so easy to achieve with crystal-controlled transmitters, hi.

It might also be worth mentioning that:

  • the Spaceweather was excellent at the time of activation
  • the core loss of the EFHW transformer used is ~1.9 dB (efficiency ~64%)
  • the antenna mismatch loss on the real EFHW is unknown (VSWR?)
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5

Well done. Frankly, I thought you would take much longer to work so many stations with just 330mW. Dunno what propagation condx were like yesterday. It would be interesting to see if you repeat that success on other activations. I wonder if 20m is better suited to QRPp than say 30m or 40m.

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Hi Colin,

Thanks for a much enjoyable story. Now you’ve got another special Rockmite for your shelf.

Beating all records in weight reduction with a minimalist 150 gram whole gear , now you can consider bringing it to higher summits without an effort!

Well done, and thanks for the QSO (peaking 589 rst) a few minutes before in 14.063, I guess not using this tiny version right now…?

Cheers, 73 Iggy

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QMX :slight_smile:

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Aha!! Sounding that loud!

QMX is powerful and nice.

Have a safe way down.

73 CU

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9

Very impressive Colin. Do you do commissions? :wink:

Is there a UK source for QRP labs gear?

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Yes.

And no, not as far as I’m aware.

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If I remember correctly I think import duty is only due on orders over £135, but not sure about the tarrif situation and the impact that would have. Mark.

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You cannot beat the sense of achievement when you do well on QRP, well done on both the low powers and low weight .

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Hi Colin,

I already thought I had caught you on rockmite…. But QMX to QMX is also very nice.

Really like your rockmite approach!

73, Peter

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Totally agree. HF QRP and 2m and 70cm via HT’s do it for me. 270 feels like a tremendous achievement (once you absorb and process the shock people actually replied to you and it wasn’t a sked or an event).

Once in a while you need to get out there and give it the QRO full-fat slipper though!

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I have a mental note to check my amplifier soon. I haven’t tried my QMX with the QCX amplifier yet, I need to give it a run on the bench. I’m concerned about input impedance on the amp. I sold my QCX rigs to raise funds for my Scottish expedition in August.

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Starting with the proposition that an Altoids tin is just too heavy, out of the question!
You’re getting fanatical about eliminating weight, and I love it!

The Rockmite could be halved in size if done in SMT, has anyone attempted this?

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I don’t know the OM, so there’s no conflict of interest (:crossed_fingers: Paul)

73 Chris

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Hi Paul,

Colin G8TMV developed an SMT version RockMite but it ended up just as big as a standard RockMite.

I started laying out an SMT RockMite but my PCB design skills were (and still are) not very developed. At the time Hans at QRP Labs was having difficulties with his QCX mini design, as swapping to surface mount capacitors had created issues with microphonics. There’s a lot of AF gain in a RockMite and I feared that I’d run into the same microphonics issues, as a standard through hole RockMite is bad enough as it is!

73, Colin

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Thanks for sharing your experience with another excellent RockMite, Colin!

I never thought I’d read that the „Pico paddle seems a bit big“ :joy:

Thanks for the QSO! I felt your signal was a bit weak, but wouldn’t have expected it to be less than 500 mW. My 5 watts look rather excessive in comparison :face_with_peeking_eye:

Keep up the good work. Hope to hear you soon!
73, Roman

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20

Adam K6ARK has done some seriously lightweight SOTA activations. Adam has used a Pixie type radio I believe, whereas I’m a fan of the RockMite circuit. A Pixie is simpler than a RockMite but with less performance.

I guess there’s levels of weight and complexity which correspond with performance, and you choose the level which suits you best. I probably was too cautious and ended up with higher performance than needed.

Maybe I should try a Pixie next time.

Great to work you on the QMX yesterday!

VY 73, Colin

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