Sunday 09 November 2014
Radio and RF |
We recently purchased a pair of Specialized Crux E5 cyclocross bikes from Primera Sports in Bournemouth which we plan to use for longer road rides and some off road and keep our full suspension mountain bikes for just off road rides.
We purchased Cateye Micro Wireless bike computers (model CC-MC200W) to use on the bikes as they are a nice and compact computer and have enough functionality for our needs to keep track of speed and the distance of the rides.
The new computers seemed to be working without any problems until we came to switch on our LED Moon NOVA 80 lights and then the signal from the bike computers sender unit stopped reaching the Cateye computer and the display showed that no signal was being received. Turning off the LED lights restored the signal so there was a problem with the LED lights transmitting on a frequency close to or a harmonic of the wireless signal coming from the Cateye wheel sender unit which blocked the bike computer from receiving the senders signal.
When we returned home we experimented with different locations of the LED lights and also the bike computer and the computer would work with the LED lights running but only if the light and the computer was separated by over one meter. As this wasn’t possible on the handlebars we removed the computers and ordered a different brand of wired computer which runs without any problems regardless of the LED lights fitted on the handlebars.
In order to try to resolve these problem and find which frequencies are being used, we wrapped a wire around the sender on the bike computer to act as antenna and connected this to our scope. When passing the magnet past the sender unit a pulse was being generated at 19.16 kHz with a time period of approx. 3.4 microseconds.
The scope screen shot below shows the pulse from the scope.
The scope screen shot below shows the pulse showing the frequency and waveform.
We then wrapped a length of wire around the Moon Nova 80 LED headlight to capture the RF being emitted by the light and when connected to our spectrum analyser there was a general increase in RF noise between 0Hz and 10Mhz.
Connecting this to the scope showed several different spot frequencies being generated with a strong pulsing signal at 7.8kHz as shown on the screen shot below.
We then tried our more powerful SolarStorm LED headlights with have two CREE led units and found that the power cable was radiating a signal with a large primary pulse and a smaller secondary pulse at 49.3 KHz. This signal was only present when the LED light was on its medium or high setting but not on its lowest power mode. The screen shot below shows the RF being generated by the SolarStorm headlights.
In order to test if it was a spot frequency or wideband noise causing the Cateye computers to fail we used our frequency generator with signals from 1 kHz to 100 kHz into an antenna near the bike computer but this didn’t stop the senders signal from reaching the bike computer. The signals being generated and leaked by the LED lights was not a “clean” signal and had a lot of harmonics and this must be causing the interference problems with the Cateye computers.
After searching for this problem online there are a lot of other posts on cycling forums relating to the Cateye wireless computers and LED lights. We don’t have any other brands of wireless bike computers to test so we don’t know if this a Cateye only problem.