Improving the coverage of the sensor radio network

The SMS gateway worked between the sensor RF network and the mobile phone network. However, it lacked sensitivity, occasionally struggling to get a signal 20 yards away.

Ciseco OpenKontrol Gateway on lid of device, with Dallas 1307 RTC implemented

Ciseco OpenKontrol Gateway on lid of device, with Dallas 1307 RTC implemented

I mounted the OKG board on the lid of the box and the SMS board in the base, unwittingly placing the sensor RF receiver between two ground planes. And a mobile phone signal source in a similar part of the radio spectrum. Which was probably not the best way to get good performance out of the LLAP sensor radio – screen it and then desensitise it with a strong nearby signal. Oops.

Improving RF reception is always about getting metal into the sky, and height

Improving RF reception is always about getting metal into the sky, and height

So I need to get metal into the sky, fortunately at the UHF frequencies it isn’t too dramatic. It’s only the top 10cm of this that has any active parts, all I did was place the receiver board at the top and take the low-frequency data and power back into the shed, But it’s a decent heft in height and I was able to detect the signal right up at the top end of the field (about 250m away).

backup soil temperature sensor, which acts morel iek an air temperature sensor!

backup soil temperature sensor, which acts morel iek an air temperature sensor!

When I was debugging this I used a small self-contained soil temperature sensor (AB in the charts) but unfortunately I’d have to bury it to make it sense soil temperature, like the sensor at the end of the thin black cable next to the drip irrigation hose. That has the radio advantage of being wired to a sensor box raised in the air, where the transmitter is.

LLAP dual temperature sensor in the polytunnel

LLAP dual temperature sensor in the polytunnel

the box senses air rather than soil temperature

the AB box senses air rather than soil temperature even though it’s on the soil

The result of the AB sensor has more in common with the air temp than with the soil temperature only 0.5cm down (the thick blue line) but you can’t bury the radio ‘cos else how does the signal get out 🙂

Of note is that even only 0.5cm into the soil the temperature is a lot more stable across the diurnal cycle compared to the night-time lows of the air temperature, good for holding 3 degrees C of chill off in this example.

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  1. Pingback: remote sensing LLAP to SMS gateway | Richard Mudhar

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