On Thu, 26 Oct 2006 09:37:27 GMT, ml wrote:

question is what is that value how do i calculate how big a battery i
need at the know constants?

Hi Myles,

It is a matter of three things:
1. Amp-Hour or Watt-Hour capacity;
2. Demand for Amps or Watts;
3. Duty ratio.

Based on your specification for a 5W rig (I assume it is a hand held,
a small mobile would be more like 20-35W) and an efficiency during
transmit of 50-70%, then your demand would be at least 10W during
transmit. Receive would require some baseline power, my guess would
be 2W, maybe less. If you listen more than you talk by a factor of 5,
then you could count on an average demand of 2W.

Divide this 2W into the Watt-Hour capacity (I will assume 100WH) and
your power source should last two days continuous use (do you plan on
sleeping?) or 50 hours of on time over any more extended period. That
is, if you sleep 12 hours, you can stretch the service time out to 4
days. If you operate only 2 hours a day, you can stretch the service
time out over a month an a half.

73's
Richard Clark, KB7QHC