lenticular

Near the end of my rides, I climb a fairly steep hill. I ride with a Garmin Edge 520 and a Garmin HRM. As I approach the hill, my heart rate is, say, 144. I start up the hill and watch my HR climb through the 150's into the 160's. Then, at the same spot every ride, my heart rate shows as dropping even though the hill remains steep. Suddenly my HR is displayed as being in the 140's, then falls through the 130's, and today it hit 112. I crest the hill, and my HR shows a believable 158.

The funny thing is that this happens at the same spot on the hill every time. As I climb, my breathing, and the effort it takes to get up the hill tell me that, yes, it is quite steep. There are no overhead powerlines, but I wonder about a Navy research facility about a mile away. I looked for HR deviation on the outbound leg, when I descend the hill, but I'm moving so fast that I'm only there for a few seconds and all is normal. The HRM is otherwise reliable.

Isn't that weird?

rsbob 

Either it is electrical interference by the Navy, a software glitch, or your HRM strap is going south. I have Garmin as well and my strap started sending wonky readings to the transceiver unit. I would be riding along and my heart rate would show 115 when I knew it should be above 130. If it starts to happen in other places, replace the strap. If that is the sole place, its EMI.

Barry2 

My Garmin speed sensor drops out every time I cross a particular bridge.
It's got to the point I'd worry if it didn't!

2.4GHz has become quite a crowded band.

Barry

cyclezen

Electrical inteference...
Same thing happens to my HRM and cell on a stretch of road where there are some overhead major transmission lines... Both devices go wacko and the HRM eventually shuts off, because the lines are there for 3/4 mile... All leads to/from the Ellwood Peaker Plant - which actually is running fulltime 100%,
Super unhealthy for residents in a new, upscale development just a 100 yds away...
Can also happen with underground lines.
Ride On
Yuri

_ForceD_

Can you give the name and/or location of the Naval research facility?

Dan

Iride01 

How old is your strap. You'd think it'd be random time for worn out straps, but certain things might trigger them to misbehave. And perhaps it's the battery getting low and that's about the time it can draw current fast enough before the voltage goes too low. The rest periods between rides just let the battery get a second breath and once again be able to supply the required current and voltage for a short time.

Possibly it's some dastardly ray the aliens from outer space are using to observe the goings on at the Naval facility! <grin>

lenticular

The facility is SPAWAR on Pacific Highway in San Diego. The hill where the HRM goes wonky is Presidio Drive. There is probably no connection, but I recall living next to an Air Force base where peoples' garage doors would open mysteriously from time to time.

Since the indicated HR is always slower, never faster, than the actual, I would guess that packets are being dropped between the strap and the computer, but not so many as to make the computer decide that there is no HRM connected.

koala logs

Never ride close to a navy or air force research facility. Next time you might end up with sore butt and you have have absolutely no clue how it happened.

pdlamb

I'm only slightly surprised, if the source is at SPAWAR, they're not doing a better job containing or shielding the source. Are there any funny-shaped towers or radomes at the airport near that spot in the road?

genejockey 

Years ago, with a Polar HRM, when I turned onto one road at the base of a climb, my HRM would suddenly show numbers in the 220s. The first time I saw that, I almost panicked! Then I thought to stop and check my pulse, which was about half of that. I realized there was something there that was screwing with the signal.

Speedskater

In the distant past, I too have seen a Polar HRM jump to about 220, with no obvious reason.

genejockey 

In addition to the jump into the 220 range at the same spot repeatedly, I remembered another anomaly - PG&E put come high voltage cables underground along one of my favorite routes, and if I rode directly over them, my HR reading would drop to zero. I can tell you, the first time you see that it's a little freaky!

I played around with the range of the effect and found if I was > 6 feet away from the center of where the cables were buried, my HRM readings returned to normal. That was using a simple Polar HRM, and I was using wired cadence and speed sensors and a Cateye cyclocomputer. Later I got a Garmin with wireless sensors AND HRM, and riding along the same stretch, my indicated speed jumps all over the place - up and down 2 or more mph. I think the electromagnetic field around the cables is disrupting the speed sensor signal and the Garmin is switching back and forth between that and the GPS for my speed. That's my guess, anyhow.