Added by haeleng over 3 years ago


I have initialised a RFM12B module by using rf12_initialize.
What is the bitrate?
What command should I use to read what the bitrate is.
What command should I use to set the bitrate to a lower value?
I like to see if I can improve the receiving distance at a lower bitrate.
Are there more tips concerning software to improve receiving distance, besides repeating a message?

Replies (2)

RE: Bitrate - Added by martynj over 3 years ago


The most relevant post in that openenergymonitor link is this:

> Lowering the bit rate is only part of the story. In brief, a lower bit rate can use a lower frequency deviation - this results in a narrower spectrum around the nominal carrier. Adjusting the RxBandwidth down to match allows less junk into the receiver section. Result - higher signal to noise ratio which is really where the best range gain comes from.
> There are limits - setting the RxBandwidth to the minimum requires that the corresponding pairs of crystals on the communicating RF modules agree closely on their versions of ‘10MHz’. A few ppm is auto corrected by the AFC - a larger ppm delta can take the received signal partly out of the RxBandwidth filter passband, causing the AFC and hence the entire packet reception to fail.
> The current settings are at a sweet spot of range/energy consumed per packet (lower bit rates of course take longer, consequently more joules eaten). If remote node battery life is not an issue and the chosen RF channel is lightly loaded, then slowing right down to even 1200baud can have substantial range gains (provided the corresponding tweaks are made as described plus probably a little crystal tuning).

In summary, lowering the bit rate can have some improvement (at the expense of higher power consumption since the packets take longer to send) - the best improvement is when this is combined with reducing the RxBW setting to match. The default bit rate set in the library initialisation is 50kHz.
In general, the very slowest/narrowest bandwidth settings are not accessible without crystal tuning and temperature compensation.