I just bought a Polar F1 HRM because it was on sale at a sporting goods store. I am worried that others' HRM's will cause interference on group rides, as the F1 is not coded. Is this true, or is it not usually a problem? Almost all of my rides are the local club rides and with others that have HRM's! Any info would be appreciated!
If the person next to you has the same model HRM and they are close enough, then it may be a problem for as long as they are that close; it probably depends on the HRM. Otherwise this isn't something to worry about.
If you wear one for a while you may develop a good sense of how pace, terrain, and how you feel correlates with heart rate; I can now usually predict mine +/-3 beats. An anomolous reading then often indicates dehydration, illness, or picking up somebody else's transmitter.