Wednesday, 22 August 2012

New RockMite 20

Tom, M1EYP, and I had a discussion about LA1KHA's PP3 challenge a while back. Tom is convinced that 20m is the best band to find SOTA chasers whilst running flea power from a PP3 battery. I had to try out Tom's theory!

I ordered two RockMite 20 kits from Dave, K1SWL at Small Wonder Labs. The kits arrived in about 2 weeks from ordering - Dave had been waiting for parts shortages. I ordered two kits as I wanted to use the parts of the second kit for another project - watch this space!

My original RockMite 20
I already have a RockMite 20 in an Altoids tin. I worked N1WPU, Ted in Stockton Springs, Maine, back in September 2011 with my original RockMite, I cherish my RockMite for that QSO, I had joked to my friend minutes before the QSO that my aim was to have a contact with a US station using my 330mW - I couldn't believe it when it actually happened! Apparently my friend is still telling the tale! I really couldn't bring myself to modify the rig for Kjell, LA1KHA's, challenge, so I decided to order a new kit to modify.

The new kit went together without any problems, but I did substitute the zener diode feeding the varicap with a 5V1, I found the original 4V7 zener did not provide enough TX/RX shift. Dave is now shipping MVAM109 varicaps with his RockMite kits, supplies of our beloved MV1662 have mostly dried up. The MVAM109 is a pretty good substitute for the original varicap, but I find it needs more voltage to provide the same capacitance.

I again decided to build the new RockMite in my usual style, using a box from Maplin. I added a volume control, as  I find this improves both selectivity and  current consumption. I removed the PA collector choke and used a 4z-1z transformer instead, I also switched out the zener/resistor regulators, using a single low drop out 5v regulator instead to supply the mixer and PIC - see previous blog entry about low current mod.

So, how does the rig perform? Pretty well I'd say! I took the rig with me on my recent SOTA activation of Great Whernside, G/NP-008. I connected the rig up to my PP3 challenge battery, now measuring under 8 Volts, and sent an SMS spot to the SOTAwatch spotting service. This was the first time the rig had ever been connected to an antenna, would I get any replies to my flea power (~89mW) CQ's? Well I did get a reply, immediately after my first CQ call, I was answered by Barry, N1EU, in Delmar, Albany County, New York! Talk about an opening score - the QSO was across 3239 Miles, which equates to 36,393 Miles per Watt! I have applied and have been approved for my QRP ARCI 1000 Miles per Watt Award (KMPW), I think I just scraped though the award criteria ;-)

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