chrisw957 wrote:Changed out my whip antennas for ones of the correct length, but I'm still disappointed by the range.
I'm using the rfm12b at 434 mhz, 4800 baud, 90 khz of deviation at full output power. Sending 16 byte packets, I can only get a few meters before I start getting bad CRCs...
I see you mentioned getting good distance from the 900 mhz version, but what are others seeing with 434 mhz?
Also, I believe here in the USA, the RFM12B at max power setting emits too much power at 434 mhz to fit under that part 15 rules.
Some suggestions.
Could be interference, I can imagine that 433 spectrum would be well used. Try moving the Frequency around a bit.
What receiver bandwidth are you using? Try 200KHz as a starting point and work in. 67KHz bandwidth on the receiver and the transmitters deviation of 45Khz should optimal for the datarate your using. too wide a bandwidth will be prone to more interference. The transmitter deviation should be smaller than receiver bandwidth.
While not normally needed you can check the tuning of all transceivers, to do this, enable and measure the CLK output with either a frequency counter or Oscilloscope, change the frequency to 10mhz, and then change the capacitance by the config command, 0x8000, until it reads exactly 10MHZ, I think around 12pf works for me. This helps to make sure that the transmitter-receiver frequency offset coming from crystal inaccuracy is minimal.
Also as a starting point for the receiver set your AFC set to auto offset independent of VDI, +3/-4 max dev, fine mode, enable offset register, enable calculation of offset.
and set your datafilter to auto mode, clock recover set, digital filter, DQD threshold is 4.
if you are not using your CLK then turn it off
Hope this helps.
Stephen...