I recently had the need to power another 10-watt rig in such a way (and with so many variables) that calculating the needed battery capacity would have been an exercise in frustration. Here are the details:
A 2m APRS transmitter (10 watts RF out) and a GPS receiver, programmed to transmit my position
How much capacity (in amp-hours) would be consumed in a 48 hour period? Keep in mind that battery voltage (from a 5AH LiPo) drops during TX and more significantly so as the battery further discharges. The constants aren't constant.
If anyone wants to take their best guesstimate of the amp-hours required to power the set-up described for 48 hours and post your value as a comment (no email, por favor), I'll send the the winner my 20m PSK31 QRPver, postage paid anywhere in the world. But - the winner must get within 20% of the correct value. Deadline is 0000Z on 19 Jan.
|The prize: 20m QRPver (PSK31)|
As with the KX2's built-in amp-hour meter, this one absolutely removes the guesswork of calculating power usage, not only in my APRS application, but for equally variable duty cycles and operating styles of using CW and SSB with any rig (even QRO).
I tested it for accuracy, comparing its displayed voltage and current with that measured by a Fluke 87. It was spot-on.