Stuart France
Active member
Does anyone out there have experience and a working design to transmit data from a cave entrance through the odd bunch of fir trees or through a leafy canopy of hardwoods and maybe around a very slight ground obstruction due to the curvature of the hillside over a distance of hundreds of metres? Power consumption doesn't matter as it will only be powered up when the sensor side wants to send a digital message, maybe once a day.
I have already tried Zigbee modules (the high power ones) but these are 2GHz and hopeless except on a clear line of sight. I got about 600m from Penwyllt with one of these transmitting "hello world" into a laptop inside the small common room - perfect line of sight but behind a glass window. We then tried the hill road above OFD1 across the valley to the cafe at Craig y Nos country park which is a kilometre through air only and just got it to work on a line of sight that didn't involve any trees provided that a stainless steel dogbowl was used as a 'parabolic' reflector behind the Zigbee whip antenna. No dog bowl = no hello world.
I'm thinking I ought to be trying VHF instead, as low a frequency as possible. For instance the 'new' 168MHz band for which there are modules. Has anyone tried these and got something to work well, e.g. with a PIC driving it?
I have already tried Zigbee modules (the high power ones) but these are 2GHz and hopeless except on a clear line of sight. I got about 600m from Penwyllt with one of these transmitting "hello world" into a laptop inside the small common room - perfect line of sight but behind a glass window. We then tried the hill road above OFD1 across the valley to the cafe at Craig y Nos country park which is a kilometre through air only and just got it to work on a line of sight that didn't involve any trees provided that a stainless steel dogbowl was used as a 'parabolic' reflector behind the Zigbee whip antenna. No dog bowl = no hello world.
I'm thinking I ought to be trying VHF instead, as low a frequency as possible. For instance the 'new' 168MHz band for which there are modules. Has anyone tried these and got something to work well, e.g. with a PIC driving it?