Summary of RFM69 output power
The author selected the RFM69HW radio module for its cost-effectiveness despite needing low-power operation. However, mixing HW and W modules caused communication failures due to Radiohead library limitations: settings above 13 dBm fail on W modules, while those below 14 dBm fail on HW modules. The datasheet clarifies that specific power amplifiers must be enabled based on output levels, a feature the library handles correctly when ranges are not mixed improperly.
Parts used in the RFM69 Project:
- RFM69HW radio module
- Radiohead implementation (version 1.71)
As I was mentioning in my 1000.1000 Hardwareselection, I have opted for the cool RFM69HW radio module. Weirdly enough, in quite a few sources (big distributor and ebay) the higher power HW module is cheaper. So there ie no reason not to get the higher power module, given quantity discounts. But I want it to operate at lower power most of times. The datasheet does not show any differences at lower power, so I had no reason not to go for the higher power module. It even says so on the features list on the front page, I can turn the power down to -18dBm.
What happens?
Unaware of the full details, frustration emerged when I started mixing in both types of modules. The Radioheadimplementation I am using (1.71) makes sure no single power value will work for both module types: over 13 dBm and a W module will not work, under 14 dBm and a HW module will not work. Digging through the code shows no problems, it does not really work as expected, but it should. The datasheet makes things more clear which power amplifier to enable based on the level and the library implements it properly. We can see there is some overlapping in the ranges as well.
for more detail: RFM69 output power
- Why did the author choose the RFM69HW module?
The higher power HW module is cheaper than lower power versions and offers quantity discounts. - What problem occurred when mixing module types?
No single power value works for both types because over 13 dBm fails on W modules and under 14 dBm fails on HW modules. - Does the Radiohead library code contain errors?
The code itself has no problems; it implements the datasheet requirements properly regarding power amplifiers. - How does the datasheet explain power amplifier usage?
The datasheet indicates which power amplifier to enable based on the specific output level required. - Can the RFM69HW operate at lower power levels?
Yes, the features list confirms the power can be turned down to -18 dBm. - What happens if you set power over 13 dBm with a W module?
The W module will not work correctly if the power setting exceeds 13 dBm.
