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jhaines0 / HoneywellSecurity

SmartThings integration of Honeywell/Ademco wireless security sensors
Apache License 2.0
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Range Issues #1

Open esdad697 opened 7 years ago

esdad697 commented 7 years ago

Honeywell sensors work to about 25' of RTL-SDR with 7" telescoping antenna near ceiling.

RTL-SDR: https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Telescopic/dp/B011HVUEME/ref=sr_1_3?ie=UTF8&qid=1487716630&sr=8-3&keywords=rtl-sdr Software running on RPi 3.

With antenna lower or range longer, works sporadically.

Not sure where the trouble lies.

Could set gain to automatic: rtlsdr_set_tuner_gain_mode(dev, 0) or manually set gain. Any suggestions on settings or different SDR/antenna?

jhaines0 commented 7 years ago

I'm using this dongle: https://www.amazon.com/dp/B00P2UOU72

Your performance is not unexpected. Things to try: Mount the antenna on a good ground plane. Switch to an antenna that is specifically designed for 345MHz. Select an SDR with a better signal to noise ratio. Replace the battery in your sensor.

Fundamentally, the on-off-keying used by these sensors is a very poor modulation strategy and will not result in very good performance.

securityguy commented 7 years ago

I'm making the assumption that you are using this for educational/experimental purposes, and not relying on it to protect people or property.

We can't expect an inexpensive SDR to have the same range as a dedicated receiver, especially if, as jhaines0 points out, the antenna is mismatched or you're in a noisy RF environment. In theory, 1/4 wavelength at 345 MHz is 20.7 cm (8.14 inches), so if you have a decent ground plane that's a good starting point. If you don't, you might double that for a 1/2 wave antenna, which is less dependent on the ground plane.

In practice, I found that fully extending the telescopic whip antenna that came with my SDR gave me better performance. I'm receiving sensors on the 2nd story of the house from an antenna in one corner of the basement. YMMV.

If all else fails, you might want to experiment with a random long wire antenna (i.e. longer than a few metres). It may drive the background noise levels through the roof, but it might work in your environment.

Plan "A" should be to put the receiver as close to the center of the devices as possible. However, if that isn't possible due to wiring, power, or spousal satisfaction issues, see above :)

The Honeywell devices have short internal antennas that often curve. Receiver antennas are usually oriented vertically, so I think vertical polarization is your best bet...but you can always try playing with that as well.

Using software to visualize the band, I've found some variations in sensor frequencies. One was centered at 344.9766, but another was much closer to 345. I doubt this is creating a range issue, but it would be interesting to see what results others get. I used RTLSDR Scanner set from 344 to 346 MHz and moved a magnet back and forth to create as many transmissions as possible.