- Passive antennas increase power and range
- No disassembly or soldering necessary
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
-59.9dB, -59.4db, -59db
-64.7dB, -66.4db, -62.8db
No passive antenna (stock)
-71db, -68.5db, -69.1db, -67.4db
- 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)
Monoprice Z-Wave Plus Door and Window Sensor, No Logo (Had a much lower power gain)
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.
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.
Hackrf One ~$300 https://greatscottgadgets.com/hackrf/
I think this is the antenna, will update after I ask my friend. https://greatscottgadgets.com/hackrf/
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
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.