Thursday, January 06, 2011

Microlight QRP

Keen followers of SOTA will have read about this on the SOTA Reflector, but during the last couple of months Richard G3CWI has been activating summits using a 30m transceiver powered by a 9V PP3/MN1604 battery. This apparently is in response to a challenge set by another keen SOTA activator: Kjell, LA1KHA (who visited us in October 2009.)

I couldn't find many details of the challenge, so I'm just assuming that it was simply to see how many activations could be made using a radio powered by one of these small batteries. Kjell is believed to be using a Small Wonder labs RockMite but Richard built his own transceiver especially for the challenge. The receiver uses a two-crystal ladder filter at the signal frequency, an NE602 mixer, a low noise AF amplifier and active lowpass filter using CMOS op-amps. The transmitter has a crystal oscillator, bipolar buffer, bipolar amplifier and FET class E PA giving 300mW output and an internal Tick1 keyer.

With this transceiver Richard has now activated 10 summits making more than 100 contacts, still using the original PP3 battery! Having established that a PP3-powered transceiver is adequate for reliable activating Richard is now looking for ultra-lightweight HF antennas to get the weight of his portable station down to the absolute minimum.

I think this is a fascinating challenge and hope that Richard will write up the experience in more detail one day, perhaps in his RadCom Portable column or in the G-QRP Club magazine Sprat. This is really what QRP is all about, reducing the equipment to the bare essentials. It also shows the value of CW as the only mode that allows you to use such simple equipment.

7 comments:

Lynn (D) said...

That's pretty amazing. I'm not much into hardware myself, but I'm looking for a light-weight, portable, 30m solution for an APRS tracker. Receiving would be a bonus, but I want something that could be taken out on a kayak and still get AX.25 or GMSK-250 (APRS Messenger) signals out into the Ether. My son (KJ4DXK) is currently on day 3 of his 5 day paddle in the depths of the Everglades with no tracking and there's a local ham that wants to paddle from here to the Bahamas across the open ocean.

Where should I go watch for ideas on the lightweight 30m antenna?

Julian said...

I'm also interested in the possibilities of a lightweight portable 30m APRS tracking solution. Unfortunately I'm not sure if the PSK63/GMSK250 experiment will ever catch on sufficiently to provide a viable network. I'm using a TNC on my HF radio now so I'm out of touch with it as I don't have a sound card connection to the radio.

I get gated during the daytime running 10W of FSK300 packet on 30m to an MFJ loop in the attic, so 5W to a good antenna should be workable. The trouble is the efficiency of antennas plummets as you make them small enough to be readily portable. Richard of course is operating from a fixed location once he reaches the top so portability isn't one of his considerations.

Julian said...

What I should have said was portability is only important to Richard in as much as he has to carry the antenna to the top and would like to save weight, he doesn't expect to operate while on the move. So he could use a dipole or end fed half wave, the clever bit is finding a really light mast that collapses down really small but is strong enough to support the center.

Fred said...

Doesn't get much lighter (or easier) than an end fed Zepp. Nearly any light weight wire will work at this power level.

Some interesting resources:
http://www.aa5tb.com/coupler.html
http://www.qsl.net/va3rr/sw30/30metres.htm

N1ZUK

Julian said...

Yes, I was thinking along those lines myself. It's what you need to hold it up in the air that takes the space and weight. Where SOTA types operate from there tends not to be a lot of trees.

Lynn (D) said...

From what I've visualized about SOTA activities, a collapsing pole that is robust enough to act as a walking stick would be ideal. I saw a presentation on VLF one time and the presenter had some sort of telescoping fiberglass pole that was amazingly light (I played a guy wire role holding it up), but I don't remember how short it collapsed to. IIRC it was some sort of telescoping fishing pole, but I could be worng.

Fenris said...

I imagine that it would be the same sort of 7m fishing pole that Richard supplies as part of his SOTAbeam kit, the collapsed pole is 1.1m long and weight is pretty low although I don't have an exact figure to hand. It's certainly less than a 1kg by a significant amount.