NCE Radio power limitation and suggestions about the NCE One Way Throttle.
“Cab Power Limitation” conversation on the NCE Yahoo Group on 02Feb06.
Ron St.Laurent asked: Perhaps I'm missing something. I read that the power limitation is placed on the NCE cabs because they have two-way communication? What difference does it make whether it has one or two way communication?
The fact is that the unit is transmitting and that's where the power limitation is applied so that other radio controlled devices on that frequency are not affected. The "one-way" or "two-way" should have no bearing.
Mark’s G’s reply.
FCC does not define power as just pure Radio Signal (RF) Strength. They permit time averaging to be taken into account. It is the AVERAGE power that they limit.
Example: You can transmit twice the RF power if you only do it half the time.
Where the one-way versus two-way comes into play depends on the protocol needs of the cab which directly translates into the power rating of the radio transmitter. To understand this, let compare Digitrax's one-way radio with NCE's two-way radio.
Digitrax cab bus protocol is such that in most cases, seldom does the command station need to talk to the cab. In fact after selection of a Loco/train, the command station no longer needs to talk to the cab for basic train operation. But on the other hand, the cabs talk to the
command every time you push a button to control the train. Digitrax took a look at that low communication protocol overhead and said 'we could make one-way radio system work with that'.
First they made a rule. You must "plug in" the cab to select a train. With that done, that permitted one to unplug the cab and use radio from that point on. Then they looked at how often does the cab need to talk to the command station. That question got reduced to: How often do you push a button on a cab? Not much at all. So by looking at the FCC rules, they were able to design a one-way radio with a very powerful transmitter which only transmits a signal when you press a button (or a command that does not need the command station involvement). In other words, the radio puts out very short burst of RF. No button, no transmission. (I have not personally verified the radio portion "no button no transmission" of the above text is 100% true because I do not have a Digitrax radio system. But I am very confident this is how it works based on conversations with others and it makes perfect sense. Non-the-less, I think everyone gets the idea.)
NCE cab bus protocol requires two-way communication to work with any standard NCE cab that can plug directly into the cab bus. The command station polls (ask) every cab to see what buttons are being pressed and processes the button into a command and then optionally updates the cab’s LCD display as needed, if one exist on the cab. Even if the person never presses a button, the cab is still asks for the status. The protocol requires a very high overhead on behalf of the command station. The command station is constantly polling all the cabs all the time and expecting an answer from every cab every time.
Looking at that protocol, there is no way to make it one-way and still use standard NCE cabs. So NCE was forced to build a two-way system to make the radio transparent to the user. When NCE looked at the FCC rules, it became clear that the command station, working through the base station, will be transmitting ALL THE TIME. So NCE was forced to do the OPPOSITE of what Digitrax could do in terms of transmitting power to meet the same FCC rules. That had to go with the minimum power level.
(The following is my personal guess as to what is going to happen)
NCE plans to offer one way radio cabs some time in the future. This is well known. But looking at it technically, to do so would mean a new unique protocol between the new radio cab and its matching base station would be required. I suspect the new cabs will work just like Digitrax one-way cabs in that transmission only occurs when a button is pressed as opposed to being ask if a button has been pressed. Thus these new one-way radio cabs will be 100% radio only operation because they are not compatible with the cab bus directly. Likewise they will need a completely different base station than the RB02. The one-way radio base station will have to translate the one way cab button presses into compatible Cab bus protocol commands that the command station can work with.
Hope this clear things up.
Best Regards,
Mark Gurries
Linear Technology
Power Supply & Battery Charger Applications Engineer/Manager
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