Friday, May 22, 2009

Tiny QRP

Everyone knows that QRP means "low power" and that the accepted definition of a QRP operator is one who uses 5 watts or less (10 watts PEP on SSB.) But to me, true QRP doesn't just mean low power, it means small, simple and low cost. Some folks who have worked DXCC with QRO and big antennas decide to do it all over again using QRP for a new challenge - but with the same antennas. To me, that's cheating. A 3 element beam on a 70 foot tower is not QRP, no matter how little power you are running.

A little interest of mine (pun intended) is to try to put together the smallest possible effective QRP HF radio station. With my MFJ Cub, wall wart power supply and a Christmas Key from Milestone Technologies I have a QRP 20m station that is pretty cute and small. However, the Cub only has a headphone output, and sometimes it's nice to be able to listen on a speaker. So I was interested when I saw a speaker for MP3 players advertised on Ebay that looked like it was MFJ Cub-sized.

When the speaker arrived, it was smaller than I imagined from the seller's picture, as you can see. It has a built-in audio amplifier and a lithium rechargeable battery, which must be recharged from a computer USB port. This is a bit of an inconvenience, and I wondered whether I could rig a power source from within the MFJ Cub so it could be powered (or charged) from the Cub's 12V supply, but I'll leave that for now.

The problem I didn't anticipate was that the jack for plugging into the Cub (or MP3 player) is captive, and folds out of the speaker. This made it impossible to plug it into the Cub at all. However, I cut the jack and a short length of cable off an unused pair of ear buds and was able to solder this to the jack (which fortunately is gold plated and very easy to solder to). I was then able to retract the jack back into its slot with the wire attached, and stick a piece of black insulating tape over the slot. The result: a tiny speaker with an attached lead that I can plug into the MFJ Cub or any other of my small QRP rigs that don't have a speaker output.

I think it looks rather cool.
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