try riding your bike on the trainer outside to determine if it is something outdoors causing the signal to be missed or if it is something that is a result of RIDING outdoors. eliminate all possible alternatives.

tommy

Thanks for the tip Tommy. I tried that and it works fine outdoors on the trainer.

I guess it's the alignment of the pick-up to within 5degrees of parallel that's the problem as the seat stays on the P3 angle-outwards more than my other bikes on which the PTap works fine. I'm wondering how the PowerTap "knows" to transmit the signal directly upwards and whether the problem is that outdoors the bike leans/moves left/right (eg. like when climbing and you rock the bike left/right) whereas on the trainer it's held directly upright and the signal goes directly up to the receiver (or close enough to it). Outdoors though the signal goes directly up (ie. perpendicular to the ground, even when the bike is leant to one side) and the receiver is missing it more often than not and deciding there's no signal (worth displaying anyway)??

i was having the same sort of outdoor issues with my polar, but then i talked to them and they told me how to ramp up the signal power so that there wasn't any interference. cars were a big problem for me. you might try calling them up and telling them the signal isn't strong enough and see what they tell you to do.

tommy

What do you mean, "ramp up the power", did Polar have you modify the trasmitter? I have a s710i that I love. I like having the speed sensor on the rear wheel for my indoor workouts, but then I have to have the watch on a stand next to the bike to get a signal. In order to wear the watch for outdoor rides, I have to move the sensor to the front fork. I'd like to be able to leave the sensor on the seat stay all the time.

yes, they had me modify the transmitter. do you have the sensor on the seat or chain stay? as far as i know, it should be on the chainstay to prevent interference.

I tried it in a number of positions with my bike on the trainer. I initially had a horrible time getting it to work. At one point I had it on the seat stay with the watch on a stand almost next to it. Right now it seems to be doing better, I can have the watch on a stand next to me, which makes it much easier to read. Should it work with the sensor on the chainstay and the watch on my wrist or aerobar? What was the modification they had you do?

Well, the PT doesn't know to transmit "upwards". The hub unit is sending out a low-level, semi-omnidirectional signal, probably not very much different in dispersion from the cardiod pattern of a common stage microphone. Within that pattern there are optimum positions for signal pickup. These will occur at certain directions and at certain distances (1/4 length, 1/2 length, or full length of the signal wavelength, or multiples thereof.) from the unit. I'm guessing that the 7 inch figure equates to one of these figures, though I have no idea what the transmission frequency is.

All of that is a long way of saying that in theory you *might* be correct about the bike movement, but I doubt the receiver is that sensitive that a millimeter one way or another will cause such dropouts. I suggest re-measuring the distance between the receiver and the hub. Being off by even an inch can cause the receiver not to recognize the signal. If that is the case, then I could further conjecture that having your bike in the trainer provides reflected signals from the stand that somehow provide correct and sufficient signals back to the receiver. Take away the stand and the unit becomes confused again because the direct signals are hitting it off phase. My best guess is the distance is off. I took care to mount mine at exactly 7 inches and have only the occasional RF interference dropouts from power lines and security systems.