In Israel, one of the cell phone providers (Orange…which almost half of the population uses) works on the same frequencys as the KOP radio modems (I guess something like 902-928MHz ). This causes situations where we would be driving the robot around, and once a kid got a cell phone call the radio connection between the OI and the robot got disconnected and we couldn’t operate it until the RC was reset.
I think this might be a problem in the regional with 10000 people and at least a third with Orange cell phones.
Does anyone know if they had this problem in one of the US regionals and how they solved it? (I doubt it though…different cell phone systems…)
Radio frequency allocations vary somewhat, country by country.
The radio modems use a US frequency allocation listed for unlicensed use.
If these frequencies overlap the cell phone allocations in a country
for an overseas regional it would be a serious problem for both
the reliability of the radio communcation and the legality of the activity.
Lets hope that FIRST has done their homework with regard to
the frequencies used by the radio modems at the regionals…
I know for a fact that the radio modems are somewhat illegal in Israel (and at first not allowed into the country by customs)…because they overlap the cellphone frequencys…but the FIRST Israel manager got some kind of permission to use them
David,
Israel and the US share the same frequency allocation in this band through an agreement with ITU according to ITU docs. The 902-928 MHz band is for a variety of services including amateur experimental communications. It is a common problem in cell phones for there to be localized out of band radiation. So it is possible that a cell phone next to a radio modem could have over driven the modem circuitry and caused it to lose handshake. Drivers in both the US and Israel should not turn on their phones when they are driving for this reason. Other services can and have interfered with radio modems. Remember that although harmonic radiation (multiples of the main carrier of a radio service) is generally specified to be 40dB or greater below the emission on frequency, 40dB below 100kW is still a lot of power (about 10 watts).
I don’t think that it was a problem with the modem bothering the circutry of the modem, cause this problem occured many times, at a fair distance from the robot (15-20 feet) and happened to multiple teams, therefore I think it is probably the frequency.
However you might be right cause it looks like you know what you’re talking about
David,
There is a design issue with most radio receivers. Localalized interference can occur with transmitters that are near in frequency but high in level. Although the interferring signal is attenuated in the receiver circuitry, the offending signal causes distortions in the desired signal but overloads the receiver input. If the receiver (in our case the radio modem) has some sort of error correction software that has built in safeguards then a period of lost communication might just shut down the receiver. I am guessing this is the case with the modems. You wouldn’t want the robot driving around without driver control when the signal is lost, so the software shuts down the system and disables the robot. It is the reason that this rule is in place…
<R103> Any decorations that involve broadcasting a signal to/from the robot, such as remote cameras, must be
cleared with FIRST Engineering prior to use. Teams may not use 900 MHz camera systems.
And this is the reason that radios are not allowed for communication and robots must tether everywhere except on the field at every event.
Several sources on the net indicate that the mobile transmit frequency range for the GSM 900 cell phone band, used by Orange in Israel, appears to have an unfortunate overlap with the radio modems used by FIRST.
i think that they give the teams attending the Israel Regional, a 900mhz modem, but the Radio towers at the event are running a different frequency. easy question to ask,
I don’t know (this is my first year on a team) but I would assume they didn’t. Are you sure they would give out different transmitters and recievers at the regional? did they ever do that before?
And just a thought that came to my mind…theoretically, is it possible to control the robot with a cell phone?
If FIRST is on top of this, and I would assume that they are, they would
pick radio channels that do not overlap the particular radio frequencies
used by Orange. FIRST monitors all of the available frequencies and avoids
those with interference. It is likely that some frequencies do not collide.
To actually control a robot with a cell phone you would have to
use the exact frequency and duplicate the communication protocol
used by the robot. It would not be very practical to do.
). This causes situations where we would be driving the robot around, and once a kid got a cell phone call the radio connection between the OI and the robot got disconnected and we couldn’t operate it until the RC was reset.