I accidentally stumbled upon a heart rate strap that was compatible with my i-magic 1904 head.
The Suunto Dual HRM strap uses ANT (not ANT+) or IND (old gym equipment standard). I bought a Suunto M5 watch on eBay a week back for peanuts mostly as it came with a Suunto ANT+ USB Movestick but also the Dual HRM strap. It was cheaper than buying a branded ANT+ USB stick alone. I've been through a few Chinese ANT+ USB sticks and sent them back due to incompatibilities. The CYCPLUS stick seems to be rebadged all over the place - cheap but it doesn't support continuous scanning and will disconnect randomly and frequently.
Anyway, the red light on the 1904 head started flashing while I was playing with the watch. As Suunto used their own proprietary ANT protocol, I presume the IND protocol is what is being picked up by the Tacx. So instead of flipping the watch and HRM strap back onto eBay, I've kept them as they work great with the Tacx trainer and the ANT+ stick is working great with FortiusANT to bridge the USB connection to use Zwift.
Are there other pre-ANT+/BT HRM straps that are compatible?
Fortius/i-magic compatible HRM
Moderator: nzuraw
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mcorn
- Directeurs Sportifs
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- Location: Bellingham, Washington, USA
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Before digital HRM's, 5 khz analog straps were very common. For a long time, you could buy them on eBay for next to nothing. There are still a few being made. Because they are not coded, you can't have more than one strap in the same area due to cross-talk. They are somewhat prone to electronic interference as well, but I found they generally worked pretty well with my Fortius and Imagic.
As I recall, Polar also made a dual strap.
As I recall, Polar also made a dual strap.
Michael Corn
Bellingham, Washington, USA
Bellingham, Washington, USA
It never occurred to me it'd still be analogue. Uncoded. 
*digs around in the drawers*
I've just put a battery in a 25 year old Polar Accurex watch and it still works. Unfortunately the HRM strap seems to have perished. I remember XC MTB race startlines now where everybody else's HRM interfered. And setting the max power beep 10bpm lower so the guy who thought the beep meant you'd blown got a surprise.
*digs around in the drawers*
I've just put a battery in a 25 year old Polar Accurex watch and it still works. Unfortunately the HRM strap seems to have perished. I remember XC MTB race startlines now where everybody else's HRM interfered. And setting the max power beep 10bpm lower so the guy who thought the beep meant you'd blown got a surprise.
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mcorn
- Directeurs Sportifs
- Posts: 903
- Joined: Thu Mar 21, 2019 12:56 pm
- Location: Bellingham, Washington, USA
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As I recall, even though the Polar (probably a T31) sends a coded signal, a non-coded 5 KHz receiver can still receive it. The Polar T31 has undergone changes over the years, but I think this is how the older ones worked. I do not believe that any of the analog handlebar receivers on the older Tacx trainers can can decode a coded HRM signal.
Michael Corn
Bellingham, Washington, USA
Bellingham, Washington, USA
Yes mine is "old" and T31mcorn wrote: ↑Sun Jul 12, 2020 2:23 pmAs I recall, even though the Polar (probably a T31) sends a coded signal, a non-coded 5 KHz receiver can still receive it. The Polar T31 has undergone changes over the years, but I think this is how the older ones worked. I do not believe that any of the analog handlebar receivers on the older Tacx trainers can can decode a coded HRM signal.