I have a technical question and a rules question about Carrier Current operation. This may not be the correct subforum, but I'm not sure where else to post this.
First, the rules question. I see mention of Carrier Current operation on this and at least two other forums. Specifically, on another forum, RFBurns posted some good information about CC. However, he mentions setting up CC systems in non-campus (non-educational) environments. I got the impression from postings on this forum that others were doing the same. Am I missing something in Part 15? I thought that this was not allowed. I'm not trying to do a "fry" here. In fact, I'd like to hear that non-campus CC operation was allowed. Someone please enlighten me.
Now the technical question. As I understand it, radiated emission of the CC system from the power lines cannot exceed 15 uV at the proper calculated distance (depending on frequency of operation). OK, assume I have a spectrum analyzer and not an expensive FIM. If you are taking a measurement with the SA connected to a 50 Ohm line, then 15 uV is between -83 and -84 dBm. How do you take an accurate measurement from a CC system when the SA is using a short antenna of indefinite length to receive the free-space emissions, and not via a nice 50 Ohm impedance cable?
Joe
Carrier Current in the medium wave band is allowed under Part 15.221 and the power level is limited by field strength measurement according to this quote from the Rule:
"...provided the field strength levels of the radiated emissions do not exceed 15 uV/m, as measured at a distance of 47.715/(frequency in kHz) meters (equivalent to Mambda/2Pi) from the electric power line..."
Determining the field strength with a spectrum analyzer ot short antenna receiving device is not something I know about.
The only "poor man's" description I have ever heard is that when the point is reached that the signal disappears into the background noise of a sensitive receiver you have found the significant spot.
..is not restricted to a campus. I ran a cc system back in the early 90s, but had never heard of neutral injection at that time. Subsequently, the signal really never left the premises.
I heard a better cc station in a small coastal town. I did not see the set-up, but was told he was running a 5 watt caarier current system. It covered the very small community, and faded out quickly when leaving the boundaries. There were no other stations for roughly 50 miles, so it seemed great to have an AM station there.
I ran an old CC transmitter into a 10 dB attenuator, and then into a crude coupler I made which was connected to the neutral.
The attenuator isolated the transmitter from the coupler.
1000 feet down the street about 15 houses away, the signal was heard on a
Grundig S350 without any trouble at all, but the Grundig is a
very sensitive radio on the AM band.
Here's something very interesting - the Grudig radio was
running on batteries. It was not plugged into the AC
line. I could only hear my station when the radio was
placed in a huge window sill on one side of the house.
That was THE ONLY place in the whole house where
there was reception of my station. I looked out the window and
then looked up. There was the power line coming into
the house. Based on that, it was confirmed (I think) that the
signal was IN the AC line, and not radiating too far
from it. I wish I had been able to plug a radio into an
AC outlet inside the house. But I only had the portable
radio with me.
I'm not a trained radio tech, so this was rewarding for me.
But, I had expected to hear my station all through the
house - and not only in that one small spot.
Bruce, The DOGRADIO Group
P.S. Sorry about the messed up
margins and the weird line spacing.
I don't see well and I'm having trouble
with this thing.