Southern California - Wireless Computers and Magnetic Field Interference

So this may sound like a physics topic, but I know many of you have Garmins (I seem to think I'm an outsider, since I don't have one, except for my crappy Edge 205). With my Blackburn Delphi 6.0, which is wireless that includes all the functions I need (altimeter), when I go to certain areas, which seem to have magnetic field, it causes weird things to happen on my Blackburn. For example, standing still, it registers 25 mph. In the same general area, my speed will go from 25, to 50, to 40, to 30, to 50, etc ... My first thought is interference with emf ... I think that because I don't want to assume my Blackburn is a piece of junk. I love it otherwise.

Does anyone else experience something similar on their Garmin, or VDO, or Polar?

I have a Suunto, which is supposed to be using some coded technology (ANT). However, when the battery is low and I'm near some strong mag field, my speed can jump from the normal 15mph to 150mph. I would've though that since it's coded, I'll either get a reading or nothing, but I guessed wrong.

I've never seen this problem when the battery is ok, nor with the heart rate though. If the problem causes the number to jump by 10x, I guess it automatically filters out 1000+ bpm. :lol:

hmmm ... I did notice my heartrate has been a little higher lately. I think about 10 beats higher than normal. I thought I was just out of shape :p

I have a Sports Instruments bike computer (wireless) that turns itself off the moment I switch on my Nite-Rider Blow-Torch! Kind of a bummer on doubles when I don't get credit (on the computer) for miles in the dark! No idea what might be causing this to happen . . .

I've been too cheap to buy a Garmin, so that's how I've avoided any problems with the Garmins!

Rick / OCRR

Miles in the dark are junk miles anyway. ;)

I have a Garmin 305 and have not yet had any problems with EM interference. I have however owned a wireless Mavic and a Shimano wireless Flightdeck that had minds of their own (yes, yes, many new batteries). They turned on and off all the time on the SART, also if I'm not mistaken, Lenny's FD does the same thing.

the 3-4 miles i ride down by the Airport in downtown San diego never get counted as my computer will not work...i have the Polar CS200....love it other than that.....it just doesn't work well down town (street light sensors?) or around the airport.

I had a VDO DS3.....hated it...the cadence wouldnt work. Couldnt even get the front sensor to work reliably...Sent it back...
I am not sure I trust wireless yet...I know lots of people love their Garmins, but many seem to have problems...
I am using a cateye AT-100, its elevation is pretty accurate as compared to the Garmins...more so in some cases!
My Shimano Flightdeck (wired) does an have RPMs it uses a calculation of wheel size and speed ( there is no cadence sensor)...I mounted a Cateye Astrale8 to test against this, and it was dead accurate except for downhill/coasting, where the Cateye registered 0 the Shimano shows RPMs...no biggie....
I am sticking with wired for now...
However that VDO MC1+ has % grade and that is interesting....and cheaper than a Garmin..

So this may sound like a physics topic, but I know many of you have Garmins (I seem to think I'm an outsider, since I don't have one, except for my crappy Edge 205). With my Blackburn Delphi 6.0, which is wireless that includes all the functions I need (altimeter), when I go to certain areas, which seem to have magnetic field, it causes weird things to happen on my Blackburn. For example, standing still, it registers 25 mph. In the same general area, my speed will go from 25, to 50, to 40, to 30, to 50, etc ... My first thought is interference with emf ... I think that because I don't want to assume my Blackburn is a piece of junk. I love it otherwise.

Does anyone else experience something similar on their Garmin, or VDO, or Polar?

So you do have a Garmin? Are/were you experiencing the same thing with yours?

So this may sound like a physics topic, but I know many of you have Garmins (I seem to think I'm an outsider, since I don't have one, except for my crappy Edge 205). With my Blackburn Delphi 6.0, which is wireless that includes all the functions I need (altimeter), when I go to certain areas, which seem to have magnetic field, it causes weird things to happen on my Blackburn. For example, standing still, it registers 25 mph. In the same general area, my speed will go from 25, to 50, to 40, to 30, to 50, etc ... My first thought is interference with emf ... I think that because I don't want to assume my Blackburn is a piece of junk. I love it otherwise.

Does anyone else experience something similar on their Garmin, or VDO, or Polar?


All kinds of things (especially HID bike lights) will interfere with wireless bike computers. This is normal. There's nothing you can really do about it unless you know what is interfering.
It comes up on the forums every couple of weeks it seems. There are many threads about it.

since I don't have one, except for my crappy Edge 205).
Note to everyone: Edge 205 does not qualify as a Garmin. :rolleyes: :p


With my Blackburn Delphi 6.0, which is wireless that includes all the functions I need (altimeter), when I go to certain areas, which seem to have magnetic field, it causes weird things to happen on my Blackburn.
I have a Specialized Turbo Pro computer. Same computer as the Delphi 6.0, sans HRM. Identical sensors. I get funky readings occassionally (I was doing 50mph while eating fig newtons at the gas station on Sunday) but it's seldom enough that it's not a big deal.

I have a Polar 720 and Shimano flight deck, orginally they were both wireless, and they would always interfere with each other. So I bought the wiring harness & base for the Shimano and no more interference.

Besides that the Polar is sensitive to the inteference caused by the EM fields caused by the high power lines.

Note to everyone: Edge 205 does not qualify as a Garmin. :rolleyes: :p

Now he tells me :(

I have a Specialized Turbo Pro computer. Same computer as the Delphi 6.0, sans HRM. Identical sensors. I get funky readings occassionally (I was doing 50mph while eating fig newtons at the gas station on Sunday) but it's seldom enough that it's not a big deal.[/QUOTE]

Delphi 6.0 comes with HRM. The reason I went with Delphi 6.0 is because it has HRM, altimeter, cadence, speed, distance ... everything you would ever want, except you cannot download the data. That's the only reason I would go with a Garmin, especially if I'm going to spend $500, as opposed to $150. Also, a LBS (Chain Reaction) wouldn't sell VDO because there is no demand for it.

Delphi 6.0 comes with HRM.
That's what I meant - Turbo Pro is the same as the Delphi, except without HRM. (has cadence, altimeter, etc)

When I go down Topanga Canyon from the town to PCH, the heart rate on my Edge jumps up to 190 - 200. I presume that's due to the low power lines causing interference rather than terror. It's the only place I've noticed that happen.

That's what I meant - Turbo Pro is the same as the Delphi, except without HRM. (has cadence, altimeter, etc)

Oh, ok .... wasn't sure about that. I think I'll try looking for VDO wired version. I don't feel like spending another $500 for a Garmin.

I don't feel like spending another $500 for a Garmin.

Then don't, Walmart online has them for 269 dollars...shipping is about 3 bucks. By the way, that price includes the HRM and cadence.:)

I've seen over 100 mph as a max speed, over 70 mph while waiting at a stop light and 0 when riding fairly fast on my wireless Cateye. I think you just can't always avoid interfering signals. My Garmin 305 hasn't given me any problems yet, but I've only used the heartbeat sensor once.

I have'nt experienced any EMF related problems with the Garmin 305, but I don't use it for speed/cadence calculation, only elev. & HR. I checked the altimeter against the summit elevation posted at 7777 ft. during the Desperado ride this past weekend, and the altimeter was dead on. I have not noticed any discrepancies with the HR data, whereas a Polar HRM I've used in the past would frequently give incorrect HR readings in the vacinity of high tension power lines.

Nor have I experienced any problems in speed and cadence readings on a wireless Flight Deck except at night when using a handlebar mounted Nite-Rider HID next to it which makes it very erratic. I've heard that mounting the light on the helmet provides enough distance to eliminate EMF interference but haven't tried it.