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Question:

Hello Keith,
I have a question on Rangemaster ground wire length and Part 15 operation.
If the transmitter is located on a rooftop and the ground wire goes directly to an 8 foot stake at the side of the building, the combined antenna and ground lead length will exceed 3 meters. Is the transmitter power then reduced accordingly below 100 milliwatts to the max. field strength level? Or am I misunderstanding the interpretation of Part 15?

Answer:

Hi,
Part 15 is a vague murky world… I could talk for hours about it. If all part 15’s were held to the strictest interpretation, then we would have to pull tabletop indoor part 15’s outside and mount them on the dirt, and people would have to take other extreme impractical measures with the 100’s of thousands of units that are already out there.

Generally I think what happens is transmitters are operated in the manner in which they were designed to operate. For example, an indoor Part 15 table top would use the house electrical system for it’s ground, (which strictly could be included in the 3 meter limit) but since the unit was certified that way, then there is an apparent allowance for the unit to operate that way.

In our case the unit is designed to be a rooftop or pole mounted device, suggested mounting and grounding examples were demonstrated in the manual and were carefully gone over together between ourselves and the FCC. This information was to be in the manual as a condition of certification. The lightning protection is very important as is the grounding to allow the protection to work. Also the tuning and power set information. All this information was gone over and is part of the approval package.

Another example is a couple companies that offer a roll of coax and an outdoor antenna you can plug into a indoor unit as an accessory, if you read part 15 it limits the (transmission line) which is a coax cable, to 3 meters, obviously 50 feet of coax going up to a roof antenna violates the 3 meter rule. More then one company offers this. Form what I understand it is for the same reason, the unit was certified this way therefore it has been apparently allowed.

I hope all that  is helpful.

Our unit is a part 15.219 transmitter which is 100mw. A part 15.209 transmitter is entirely different, it would not have a removable antenna, not have adjustable power, would have a max field strength, but everything would come preset. An example of am 15.209 transmitter is a microphone toy.

Something else, in your question you are assuming that the entire ground connectivity is included in the "ground lead" The definition I have understood from the FCC generally pertaining to all Part 15 transmitters is that the "ground lead" is the short length of wire that connects the transmitter to the local ground. What the local ground is isn't clearly defined.