QRP or QRO for portable ops?

When considering a first rig for portable ops, a QRP radio is a common choice.

Small size and weight coupled with low current (and therefore small battery requirements)  make it a very attractive prospect.  In some situations, where weight must be kept to a minimum, it is pretty much the only choice.

In other circumstances though, where more weight and bulk can be tolerated, it may not be the best choice, as low power will limit the contacts you can make. For many, the challenge of this is what makes it fun, but for newcomers it may be discouraging.

To get an idea of the difference power makes, I ran some predictions for the 20m Band using 5W, 10W and 100W SSB.

In the diagrams, Dark Blue is 10% likelihood of contact and Pinkish is 60%.


Based on these predictions, the QRP SSBer would have had a pretty disappointing time.

What Battery?


Sealed Lead Acid batteries have been the mainstay of portable power for a long time. While not inexpensive, they are not outrageously priced, and their voltage is a good match for Amateur Radio gear.

They do however have many disadvantages:

  • Lead is a dense element, good for Nuclear shielding, less so for humping about.
  • The voltage drops significantly during the discharge cycle.
  • Deep discharge can badly damage the battery, reducing its capacity.
  • In normal use you will get much less than the rated capacity out.

Amateurs have long looked for good alternatives, and currently the lithium iron phosphate (LiFePO4) battery fills the frame nicely, now that prices have become more reasonable.

These cells have a working voltage of 3 – 3.3 Volts, so 4 in series give 12-13.2 Volts, which is a great range for Amateur equipment. Best of all, the voltage  stays in useful range until it is nearly fully discharged.

This means that the useful energy you get out is much nearer to the Ah capacity of the battery than for Pb cells. Also your equipment doesn’t have to cope with a sagging input voltage.

The C rating shows maximum current draw, C x Capacity = Amps, so 30C x 4.2 = 126 Amps for the above battery.  This seems optimistic for such a small battery, but it gives me confidence that using it for a 100W rig peaking at 23 Amps will be fine.

4.2 Ah won’t run a 100W rig for very long, but I find having multiple 4.2 Ah batteries and swapping when needed is more flexible than just having a big one.

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