Zigbee 2.4 GHz experience

Hi folks,

I wanted to share some experiences and thoughts about some Zigbee tests I've done recently.

I purchased from a vendor a 2.4 GHz Zigbee kit, and programmed 2 boards in order to do following ping test:

  1. The first one is the PAN coordinator. 2. The second one is a simple device that joins the PAN coordinator. 3. After joining the coordinator, the device sends a 64 byte message to it. 4. If the coordinator receives the message, it reverses it and sends it back to the device. 5. If the device receives the reversed message it increments a counter, blinks a led for 1 second, and proceeds with the next ping. 6. The test ends after 300 ping sessions (300 seconds).

The 2 boards were programmed to transmit at the maximum RF power, and the pcb antennas were the typical F-shape.

Test A (location: house with 3 floors)

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  1. I placed the coordinator at the ground floor.
  2. I started to walk, at the ground floor with the device in my hands.
  3. I noticed that if between the two boards there were more than 3 walls, the led stopped to blink.
  4. Then I went out and started to walk in the garden, and noticed that every once in a while the led stopped to blink.

Test B (location: house with 3 floors)

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  1. I placed the coordinator at the ground floor.
  2. I went to the second floor and started to walk with the device in my hands.
  3. I noticed that if I was in the vertical axis of the coordinator, the led blinked, but if I moved into a different room, the led stopped.

Test C (location: house with 3 floors)

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  1. I placed the coordinator at the ground floor
  2. I went to the third floor and started to walk with the device in my hands.
  3. The led did not blink at all.

Test D (location: 100 square meters house with 1 floors)

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  1. I placed the coordinator in the kitchen.
  2. I placed the device on the bed of my room.
  3. The distance between the 2 boards was 6 meters, and there were 3 walls between.
  4. I noticed that the led blinked regularly.
  5. I than placed the device in the closet of my room, and noticed that the led stopped to blink.
  6. I then moved around and noticed that the blink would blink.

These tests make me not very happy. I expected for the 2 boards to cover a longer distance, and I'm gonna repeat these tests with a different antenna, in the next few days.

I heard that the 868 and 915 MHz Zigbee modules cover longer distance but they transmit over a single channel and the RF signal is not spread spectrum modulated.

Comments are welcome.

Enrico

Reply to
zigbee
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snipped-for-privacy@libero.it =D0=BD=D0=B0=D0=BF=D0=B8=D1=81=D0=B0:

your observations are correct, 2.4Ghz low power transciever with PCB antenna will go through no more than couple of walls, and will work the best within a room. on open air you can achieve up to 70-80 meters.

Best regards Tsvetan

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Reply to
tusunov

a écrit dans le message de news: snipped-for-privacy@m7g2000cwm.googlegroups.com...

...

Hi,

The first question, as usual with RF, is antennas : Which antennas are your using ? 1/4 wave or patch antennas ? With 1/4 wave the ground plane is key, how large is-it ? If it's too small than a virtual ground (something like a

1/4 wave open wire connected to GND, opposite side to the antenna) can help. Antenna orientation is key too... With patch antennas take care of the radiation patterns and polarisation : Usually they are not isotropic... I would recommand, prior to "real" tests to monitor the RSSI level of the receiver (assuming your devices can provide this information) and to play with antennas, ground and orientations. Then chipsets : from Zigbee chipset vendors to Zigbee chipset vendors you can have as much as 10dB variation in RF performances. Selects the good one... Having said that the coverage you've got doesn't seems far below what I would expect in 2,4GHz, but it also depends on the wall's materials. Up to 200m in open air is quite common but down to 10-30m indoors depending on conditions. Regarding 868/915MHz Zigbee there are a couple of products but this isn't the mainstream Zigbee... May be another question : Why are you using Zigbee ? If you need Zigbee for itself (meaning for compatibility with other devices) then I guess you can't change freq band. If you don't need compatibility then other RF protocols can provide you a far longer range (we've developped applications with up to 2km open field coverage with 868/20mW low cost frequency hopping transceivers).

Friendly, Robert Lacoste

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Reply to
Robert Lacoste

Hi Robert,

thanks for your reply

The development kit comes with 2 antennas:

- pcb patch antenna - ordinary 2.4 GHz antenna

I don't know how large the ground plane is. I purchased the development kit and I assume they made the best design to foster their products.

ok

I see...

I can monitor the RSSI level, but I won't sell a piece of my products if the 2 boards don't communicate.

The Zigbee protocol deals with this kind of problems, by means of routers. That is, I may modify the topology of the network by introducing a third device (the router) that acts as a router and that extends the range. The only problem is that routers can't be battery powered.... They must be always on.

Really that much?

I see...

I'm using zigbee because I use standard products whenever I can. The IEEE engineers have designed important RF standards like 802.11 (WLAN) and I trust them.

Enrico

Reply to
zigbee

snipped-for-privacy@libero.it ha scritto:

Di quale marca e' il kit?

-- Per rispondermi via email sostituisci il risultato dell'operazione (in lettere) dall'indirizzo

Reply to
Fabio G.

Fabio G. ha scritto:

Hi, I don't wanna say it. It wouldn't be fair...

Enrico

Reply to
zigbee

There is only one channel in 868 band. There are 10 channels in 915 MHz band. The signal is DSSS modulated, although using a different chiping sequence to 2.4 GHz.

Cheers, Jon

Reply to
jon

Does your kit have a rubber duckie antenna? They are very directional. The pattern is a donut (torus) with the dead axis along the direction that the duckie points.

You really should not expect a duckie to go up several flights.

Some vendor's boards have both the F shaped PCB antenna and a SMA connector. If so you should try it.

Also note that the TI/ChipCon 2430 kit, does not include ZigBee, only the lower level IEEE protocols.

What were the houses made of? It is a lot easier to get through normal wood stud and plaster than stone or concrete.

You realize that 2.4 is not a good frequency for long distance for many reasons. The first is that it was available for use for microwave ovens 40+ years ago because it is the resonant frequency of water. And it was ideal for microwave ovens because it is the resonant frequency of water.

But water. plants, people, animals, etc. all absorb it.

--
Pat
Reply to
Pat Farrell

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