Z-Wave Antenna

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  • Passive antennas increase power and range
  • No disassembly or soldering necessary
  • Inexpensive

I’ve been experimenting with my Z-Wave Plus system to increase the range of my battery powered door/window sensors. I use them to monitor my rat/mouse traps and needed more distance. See my other instructable https://www.instructables.com/id/Wireless-Mouse-Tr...

If you don't want to read all the tech info below, try taping a straight 8" copper or piano wire to a sensor and see if it increases the range.

Passive antennas (thin copper wires) were attached to the sensors and tested for signal strength with a Hackrf One SDR (Software Defined Radio). Lengths of ¼, ⅝ and 1 wavelength were compared with no antenna. The ⅝ wavelength antenna performed the best, it delivered ~4X more power on one of the sensors! Your results will vary, the second sensor by a different manufacturer had a small power increase. Below are the results in dB. dB is a log scale so a 3dB increase in power is 2x the power. For example if you go from -50dB to -47dB the power has increased by 3dB or doubled.

Power Levels were measured at 916MHz US Z-Wave PLus frequency. For each measurement separated by a comma in the data below, the door sensor was triggered ~10 times and the peak of the 10 triggers was recorded.

916MHz Peak Power Test Results

5/8 wavelength passive antenna (approximately 4X the power of no antenna!)

-55.6db, -55.4db, -55.6db, -55.6db, -56.3db

1 wavelength

-59.9dB, -59.4db, -59db

1/4 wavelength

-64.7dB, -66.4db, -62.8db

No passive antenna (stock)

-71db, -68.5db, -69.1db, -67.4db

Note

  • I'll add a picture of the antenna soon, imagine an 8 inch wire taped to the front of the pictured sensor.
  • Z-Wave and Z-Wave Plus use the same frequency. Z-Wave Plus is the newer version with longer range and better battery life so get Z-Wave Plus if you can.
  • A passive antenna attached to the Z-wave hub may help also, I'm trying to figure out a way to test this. Perhaps rebooting the hub or sending a status message to the sensors would force the hub to transmit.

These are the two sensors I'm using.

Monoprice Z-Wave Plus Door/Window Sensor, NO LOGO (This one had 4x power gain with the 5/8 antenna)

https://www.monoprice.com/product?c_id=122&cp_id=1...

Monoprice Z-Wave Plus Door and Window Sensor, No Logo (Had a much lower power gain)

https://www.monoprice.com/product?p_id=24259

Step 1: Making a Passive Antenna

Find your Z-wave frequency in the wikipedia list below. A lot of countries have 2 frequencies, if you are not sure what frequency your Z-wave device is on pick the average of the 2. Most documentation says that the US frequency is 908.42MHz, I measured both my sensors at the second frequency 916MHz.

Z-Wave frequency list https://en.wikipedia.org/wiki/Z-Wave

Take your frequency and put it in this calculator link below to get 1 wavelength and then multiply it by ⅝ to get 5/8 wavelength, this will be your antenna/wire length.

https://www.everythingrf.com/rf-calculators/freque...

Here is how to calculate length for the 2 US frequencies

Z-wave plus 908.42MHz : wavelength = 0.33001526m = 12.99inches : ⅝ wavelength = 8.11inches

Z-wave plus 916MHz : wavelength 0.32728434 = 12.88inches : ⅝ wavelength = 8.05inches

Cut a small gauge copper wire or piano wire to the 5/8 wavelength you calculate. You can get piano wire at the hardware store, get the thinnest they have.

Tape the wire to the side of the sensor and test!

Tip: For longer range, try pointing the front of your z-wave hub at the furthest sensor. I have Samsung Smartthings v3 hub, their website says the strongest reception is from the front. Also the orientation of the sensor to the hub will affect the amount of power transferred. The door/window sensors should probably be mounted vertically if possible. I'm not sure which way the antenna inside the hub is mounted, the sensor antennas should be parallel to it.

Step 2: How the Measurements Were Made

The first picture is with the passive 5/8 wavelength antenna taped to the front, the second picture is with no antenna.

I used a Hackrf One because I could borrow it from a friend. It’s overkill for measuring Z-wave, there are cheaper SDR’s that should work though I’m not familiar with them. You need one that will measure frequencies in the z-wave range, ~850Mhz to ~950Mhz. If anyone figures out how to measure with a less expensive SDR please comment.

Measurement Equipment

Hackrf One ~$300 https://greatscottgadgets.com/hackrf/

https://www.seattletechnicalbooks.com/hackrf

I think this is the antenna, will update after I ask my friend. https://greatscottgadgets.com/hackrf/

Measurement Software

I used this free spectrum analyzer, ‘Pavsa hackrf spectrum analyzer’. It was easy to setup, was reliable and worked well. https://github.com/pavsa/hackrf-spectrum-analyzer

Measurement Settings

Set the spectrum analyzer to start just below and end just above your z-wave frequency, for me it was 915Mhz to 917Mhz. I played around with the number of samples and FFT Bin (Hz) until I got consistent measurements, 5000 Bin (Hz) and 65536 samples worked well. On the chart options tab choose ‘Waterfall enabled’, ‘Show peaks’ and ‘Persistent display’, and set ‘Persistence time’ to 60 seconds.

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    5 Discussions

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    mnl1121

    19 days ago on Step 2

    I'm not sure the purpose of this being that zwave is a mesh network. If you have range problems the cleaner solution would be to just add a repeater, or better yet an excuse to add another mains powered device (which has to be a repeater as well). This will solve any range problems along with expanding your network.

    1 reply
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    kelpchexmnl1121

    Reply 17 days ago

    Hello! For sensors covering detached powerless structures having more range from the sensor is critical. In my case the z-wave plus mouse trap is under a hot tub about 30' from the house, with no outlets. From what I've experienced, if the distance were any further the signal would probably not reach a repeater inside. I moved my hub to about 40' away and with the passive antenna mod I'm getting reliable communication.

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    RandallM28

    19 days ago on Step 2

    Also try adding a reflector on the backside ( opposite side of the receiver ) of the driven element to give it a yagi / beam characteristics focuses more of its energy in one direction without wasting it in a 360 degree like a single driven element antenna does. Most yagis are half wave element lengths I believe. But spacing is critical for optimum results. Even just a aluminum pie pan will work to. Like a parabolic dish basically.

    I am not sure of the formula for spacing and length but a reflector is normally longer than 1/2 wave. Its a lot of antenna modeling software available. Although you can easily tinker with a pie pan or dish type reflector adjusting the spacing and I bet you will see better results.

    another design is a corner reflector but it requires more precise spacing and element lengths. Aluminum pie pan should be real close to optimum size on 900mhz.

    maybe try searching for 900 Mhz parabolic dish for designs.

    I just built a vertical antenna for 30 Meters ( 10.149 Mhz ) for APRS. I love building antennas from wire and hardware I have laying around my shop! All of my HF antennas and even some of my VHF antennas I built myself!

    good luck and have fun! =]

    de WW5RM

    1 reply
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    kelpchexRandallM28

    Reply 17 days ago

    That sounds like a good contest idea, 'Z-Wave Extreme Range Contest'. Use any passive antenna means available on the hub and a standard battery powered sensor to increase the range, repeaters/mesh not allowed. You must have 10 out of 10 successful sensor events in a row. Winner will need to verify by video and gets bragging rights. Note: Modifying (soldering) the actual antenna in a sensor or hub is ILLEGAL according to the FCC. Passive 'helper antennas' are legal, that's what I have done with the wire.

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    jjwatmyself

    18 days ago on Step 2

    Excellent discovery and very interesting application with the traps