220V Cable: with the antenna or through the arch?
We have often raised the question of whether it is a good idea to run a 220V power cable with a load connected at the other end through the TS antenna grommet where we house our UHF cables and antennas. Since we use protective grommets to protect the antennas and to run the UHF cables to each antenna, why not use them to bring us electricity from a generator, switchboard, or socket…?
Those of us who began sports timing years ago with high and low frequency systems know that timing systems in those days were seriously affected by external electromagnetic interference.
We still have 4 Ethernet-to-fibre optic converters in the warehouse that we used with our low-frequency timing system because it was terribly sensitive when you connected the sports timing equipment to anything connected to the electrical grid. I’m not talking about connecting timing equipment to a power source; I’m talking about connecting it to a laptop running on battery and connected by USB to the printer. Yes, circumstances like that result in common grounding and electromagnetic noise couples in.
Why were sports timing systems so sensitive?
Let’s start with a little theory and then finish with a conclusion that will help make our sports timing better.
Harmonics, the great enemies of any sports timer, are simply a distortion of the electric current reaching our equipment. This distortion comes from electronic devices that consume power in a non-linear way. Poor electrical installations, overheating and degradation of insulation, poorly maintained asynchronous motors, vibrations on electrical switchboards, waveform deterioration… are just a few of the reasons why they might occur. From the perspective of sports timing equipment, a motor and its converter are viewed as a non-linear load. Can you imagine how the motors of the inflators affect the quality of the power signal received by the timing equipment?
Harmonics are distinguished by their amplitude or power and their order. A third-order harmonic has a frequency three times higher than the carrier or principal frequency. A motor will add in harmonics depending on the number of poles or revolutions per minute that it has.
If we consider that the general electrical grid operates at 50Hz, that a motor can run at 1,000 rpm and that a low-frequency timing system operates at 125,000Hz, we can see that they are multiples and that the signal feeding our timing equipment could carry unwanted harmonics. Years ago, by using Ethernet-to-fibre and fibre-to-Ethernet converters and running the latter converter on a battery (a battery is a perfect power source without noise or harmonics), we isolate the timing equipment from the electrical grid and we’ll be able to do our timing without a lot of problems.
You might think that a such a high-order harmonic wouldn’t affect anything, but nothing could be further from the truth. With the UHF timing chips that we work with currently, the readers are able to detect them at around -80 dBm! What does that mean? Imagine an omnidirectional camping lantern, i.e., that emits light in all directions. If you were to take a small mirror, the size of a chip, how much light would you be able to reflect with a mirror that size? Well, something like that happens with the chips, but with an electromagnetic signal instead of light. Every -3 dBm means that you’ve lost half the power. In other words, if the chip transmits a RSSI (Received Signal Strength Indication) of -3 dBm, this would mean that it’s transmitting half of the power transmitted by the reader. If it transmits -6 dBs, it’s transmitting a quarter of the power, and so on. A sensitivity of – 80 dBm would mean that the harmonic received at the frequency of the reader could be devastating even though it is a high order frequency.
I’ve mentioned before that the RFID at low frequency operates at 125 KHz. The RFID UHF GEN 2, as I’ve mentioned in another article, works in Europe at 865.6 and 867.6 MHz, around 7,000 times higher. Will this affect the signal both on UHF and on low frequency?
Another of the reasons that concerns us is that they can affect the performance of the antenna. At the end of the day, almost anything can affect the antenna’s operation. Why wouldn’t antenna performance be affected by a power cable just a few inches away and parallel to the UHF cables?
Experiment and conclusion
We conducted three experiments:
- Proposition: first we measured the behaviour of 3 different antennas with a 220V cable with no load and with different loads; bulb, dryer and a small motor. Conclusion: it didn’t affect the performance of the antenna in the slightest. The antenna transmitted normally in all cases.
- Proposition: using the Thingmagic M6e Noise Floor parameter, we measured the same cases as above. Conclusion: it didn’t affect the intensity of the noise that Thingmagic is unable to filter in the slightest.
- Proposition: finally, we went to a race with around 1,500 people were bib tags were used for detection. At the finish line, we placed a 220V cable and a load, passing through all the grommets, together with the antennas and in contact with the UHF cables. Conclusion: the finishing line took 1589 readings and the backup with the cable took 1588; very normal, both reading well above 99% of the finishing times.
As a conclusion, in the absence of another test with different motors with different numbers of poles, we can say that running a 220V cable through the Timing Sense cable grommets with antennas doesn’t affect performance in the slightest. I hope you’ve enjoyed it and I invite you to ask me questions; you can ask them here on the post or privately to: firstname.lastname@example.org