Tech Talk – Not all tags are equal

Of the passive transponders on the market there are advantages and disadvantages between types for sports timing. We are often asked to provide a solution that can time everything from running to kayaking and even windsurfing. Each sport has its own requirements in terms of athlete speed, density and where you can put the actual transponder. Some timers wish they could surgically implant a tag in the athlete negating the old complaint, “I left my chip back home”.

Basically there are three frequencies that the bulk of RFID transponders work in, these being low frequency (120 to 140 KHz), high frequency (13.56 MHz) and ultra high frequency (860 to 950 MHz).

The low and high frequency transponders (or tags, as known in the RFID industry) work well in close proximity to water or the human body. They work in the electromagnetic energy region and these waves can pass through water but not metal. This makes these tags ideal for events where the athlete has to wear a tag on the ankle (ie. Triathlon).

On the other hand, UHF uses electrical coupling and these waves can be blocked or detuned by both liquids and metal. A huge investment has been made on UHF tag design to overcome these problems with the best solutions using a small battery to improve backscatter signal, or mechanical means like using a spacer to separate the tag from the offending material. So why do we want to use UHF tags? There are two primary reasons being low cost and huge read rates.

Firstly the UHF tag has the lower cost due to its light weight and ease of manufacture in large quantities. The UHF tags available today pretty much follow the Generation 2 Class 1 EPC protocol which is an industry wide platform adopted by almost all reader and tag manufacturers. Despite some differences in frequency regulations between countries, UHF tags can be read in Europe (866Mhz) as well as in the USA (902-928MHz). This uniformity across the industry has resulted in small passive UHF tags being available for less than 15c each. However high performance tags like the PowerT that RFID Race Timing Systems recommends will cost more due to the added battery and size, but still be lower in cost than the lower frequency transponders.

The second reason UHF is so attractive is the ability to transfer large amounts of information between tag and reader in a given time. This means advanced anti-collision algorithms can be employed to allow one reader to interrogate hundreds of tags in a second using just one antenna.

So, do we think UHF tags will dominate sports timing in the next 5 years? The answer is an emphatic yes with a footnote. We do not see UHF being an alternative in the near future for timing triathlon. Even a battery assisted passive tag like the PowerT has trouble being read on the ankle underneath a wetsuit! We think that timers will continue to use low frequency or active tags for triathlon for a long time to come and that is why our HDD and Dual Antenna Systems continue to sell strongly.

But we will make a bold statement and declare that 95% of the worlds running events will be using some form of UHF disposable tag in 2 years time

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