Sports timing: the journey of the chip from the shoe to the shirt back
Before explaining what’s near-field and far-field in sports timing, let me make a short introduction for you:
Almost all sports timing systems for cycling, running and triathlon, are passive. This means that the chip doesn’t carry any type of battery. It is loaded with energy emitted by the antenna of the timing system.
The chip timing trip from running shoes to bib number
Why the chip was placed in the shoe before and could read up to 60 or 70 cms max, and now it is placed on the bib number and can be read from some feet away? With your chip timing system, in fact, if you separate the chip from the human body, you can read up to 6 or 8 meters. Ideally, chips are being read even from 100 meters away.
The reason is very simple: Timing Systems like Championchip, HDD of RFID Race Timing Systems, Ipico, the old Dag system, Passive Tranasponders system of Winning Time… work in near field. Timing Sense, Chronotrack, MyLaps, Time-7 and any other system in the UHF frequency range, work in far field.
That’s right, but…What’s “near field” and far field about?
I’ll try to explain that briefly and if you don’t understand anything don’t panic. You can find the consequences for a timekeeper and where we can see it below.
Near field: These type of fields are predominantly reactive and theoretically don’t radiate. I say “theoretically because the antennas do. An induction current or similar to a transformer inductive coupling occurs. Here the signal behaves like a soap bubble about to pop out, but it neer comes out and eventually returns. During the first half of the signal cycle, the power goes out from the antenna and during the second half of the cycle it returns. Therefore, we are talking about short distances.
Fields E and H are in phase and as they are orthogonal , the emission occurs. Well, we can say that we would build the soap bubble, and it will come a time in which it will be separated from the antenna and it will start travelling.Then, the antenna would radiate, and we want to obtain the maximum level of radiation inside of the legal framework.
For reasons out of reach of this post, the Q parameter is more stable in the near field than in the far field for the frequency range that we are talking about. This is why, unless the chip is detuning due to the proximity with the human body, it will always work better in near field than far field.
So why the chip is used on the bib number if in far field the readings are worse? Simple, because the techonologic progress has solved this and the chip is much cheaper. Nowadays great UHF systems (the big majority suck) read better than near field systems. We had to deal with new problems but it has resolved other big timing problems.
Near field systems
It does not affect the human body, neither the rain nor a wet shoe. It can read with water as far as it is not conductive.
The fact of wearing the chip in the shoe will not make runners shadow each other.
Far field systems
Price; Chip prices have sharply fallen. As they are a standard in the industry, there are more companies producing them. Ipico, for example, is proprietary protocol and will never cheapen that much.
More distance; As it is a radiate system, you can detect the chip at a much longer distance.
Attention! This works in cycling races because it avoids the problem that many of us had when a runner came into the goal without pedaling, with his own inertia, and the chip was left in the uppermost leg. But it might happen that you receive more than one reading and that some of these are from several metres before the crossing line. In Timing Sense we have developed a filtering system based on a time window in which we always keep the optimum reading.
Lower incidence of the ground: The ground is an inexhaustible source of electrons and there are grounds with magnetic components. All this, should affect more in far-field, ultimately affects less due to our revolutionary new antenna ground plane.
Speed: good UHF systems no longer suffer in starts as the frequency at which they operate is very high compared to the old systems of near field and low frequency. ChampionChip was able to solved it by placing many reader antennas in a square metre, but the UHF system does not need this. It has an anti-collision system, called Aloha with slot, that makes the most known readers, read over 500 chips per second under certain circumstances.