Grouding Part 15 and the FCC

Thanks for doing all of this research! This is the main reason why I'm still hesitating about starting up my station. Once I get some clear rules, all I need to do is purchase the equipment, have it installed, and away we go!

Like many Part 15ers I am running groundless but forever dreaming about running ground radials. Now it may become a moot point, if radiation is disallowed.

" I am hoping basically the statement will say that if the ground radiates it is not OK, if it does not radiate it is allowed. But we will have to wait until it comes out to see for sure what it says..."

First, Thanks for chatting with the FCC. My concern is how the FCC determines that the ground is or is not radiating. And that being said, how dows a Part 15 Op measure that.

73, me

Most of you guys are engineers and really know RF.
I'm just a guy who casually dabbles with radio.

So here's a few questions, if they are really irrelevant
don't worry, you don't have to reply.

My crystal set picks up radio stations with no batteries
because of the potential difference between ground
(zero RF energy?) and the antenna (RF energy.) So is
RF ground IN THEORY supposed to mean that the ground
wire has no energy in it at all? Or energy that is so close
to zero that it is not important in the real world?

I'm just asking because I don't know. I have a great
respect for all you guys. I have learned more about radio
from this board than any other source I have come
across in a long time.

Very best wishes to all of you.

Bruce, MICRO1690/1700

Ground is a term generally taken to refer to a common reference point. When you measure voltage it is commonly measured with respect to ground meaning one of your meter connections is to that common reference point.

Therefore other points not connected directly to ground may show a voltage with respect to ground. In a perfect world if you measure two ground points you will show no voltage or current.

This is not to say there is no current flow (energy) through a ground point. To prove that simply break the circuit connection to ground and measure across that break. A volt meter will show voltage, an ammeter will show current.

The ground connection for your crystal radio is effectively in series with your antenna and RF currents flow through that ground to the antenna.

An antenna ground radial system will have current flow through it. Radio engineers can troubleshoot antenna ground radial systems by measuring the ground radial currents, looking for differences in radial currents.

So we generally refer to ground as zero volts because we are comparing it to itself.

This analogy will change with frequency and resistance as a voltage can develop between two ground points for various explainable reasons. Ask any electric lineman why he would "HOP" away from a downed power line rather than "step" away.

Thanks MRAM!

I appreciate the explanation.

Best Wishes!

Bruce MICRO1690/1700

There is nothing particularly mysterious about "ground." The earth is a conductor of electricity. When compared to any metal, it is a very poor conductor. Salt water conducts about a thousand times better than dirt, but even salt water conducts thousands of times worse than metal.

It was Marconi who invented the kind of antenna commonly used with Part 15 AM. One of the two terminals of a transmitter output is connected to the earth, and the other terminal is connected to the bottom of a vertical rod. The vertical rod and the earth form a capacitor. The transmitter causes current to flow through this capacitor. The current flows into the rod, through the air into the earth, and then into the transmitter terminal connected to the earth.

The RF current flowing in the vertical rod produces radiation. Practically no radiation is produced due to the current flowing through the earth. A very short rod (compared to wavelength) produces very little radiation, and a longer rod produces more radiation.

If the transmitter is not connected to ground directly, but through a ground wire, the RF current through the ground wire also radiates. The ground wire makes the antenna longer, and therefore a more efficient radiator. It is the increase in the effective antenna length by the ground wire that is an issue with the FCC. Section 15.219(b) limits the total length of the antenna, transmission line, and the ground wire to 3 meters. In the Ken Cartwright case, the FCC considered the 40 foot tower on which the transmitter was mounted to be, in effect, a ground lead (or ground wire).

Hopefully they will take all the ideas expressed here and no or no go them.

things such as an 18 inch wire to a lightning arrestor then a ground from arrestor to ground? Legal or not Legal?

Toroid in line 18 inches from transmitter ground lug to reduce radiation on line? Legal or Not Legal?

there are a few other idea's that have been tried here as well.

i think the FCC Engineers should study these forums and the idea's expressed and then put that into a Q&A format and whether it is or isn't legal.

sort of like a FCC Bulletin that has installation guidelines for elevated and ground mounted installations.

Lets face it. a lot of us mount our Tx up on towers because hamiltons and other certified transmitters cos about $1000.00. We don't want johnny pipe head coming into our yard and ripping the transmitter out of the ground and taking it to a pawn shop to get money for his smack.

then there are those who live in apartments that are themselves elevated. what are those guys suppose to do?

these are questions which need to be answered. i think the FCC has enough of a knowledge base now to answer most of the common scenarios that will come up.

but we know how big government is they can't find their own behind even if you give them a map and flash light.

Antenna knowledge is pretty rare, even among EEs. Most EEs took a course in electromagnetic fields and waves, and then they quickly forgot everything they learned in that class. Those EEs who know about antennas most likely didn't learn about them in school. They might have learned about them at work, or through self-study. The EE's college education usually gives him the math background needed to understand antenna theory, but not much antenna theory itself.

If there is any group that has EEs who know antennas, it should be the OET Laboratory staff. They will probably be the ones who write the guidelines that Hamilton says are coming. A bit over a year ago, John Reed made a big error in an opinion that was posted on this and other forums, and he caused a panic among Part 15 hobbyists. Then a member of the OET Laboratory staff corrected Reed, and the panic subsided.

The OET Laboratory staff should be able to come up with good recommendations without consulting the forums, which have a very wide range of opinions.

Interesting. I have a long background in compliance testing, and when I offered up an easy solution for the home broadcaster to determine compliance to Part 15 regs for FM radio, I was attacked by our friend. No help from from the group here. You guys simply re-inforced his position. Do a search on this site.

The whole subject of grounding in actual earth spans so many variabilities that it has electricians hopping, because they aren't sure. Trying to formalize standards about such a fluid topic is like nailing jello to the wall.

"The whole subject of grounding in actual earth spans so many variabilities that it has electricians hopping, because they aren't sure. Trying to formalize standards about such a fluid topic is like nailing jello to the wall."

I remeber going to an EMC seminar hosted by Glen Dash. The topic was: "Ground is not Ground The Earth Round." 🙂

That is a good one, I like that.

1. Any lead , not choked, above actual earth becomes part of the radiating system and can be described as "antenna". You can insert the transmitter anywhere you want it makes no difference. Give me 30 feet of ground wire with 2 inches of antenna any day over 9' of antenna.

2. A ruling by the FCC on this is just what part 15 didn't need. If they keep to the intent then all antennas will be less than 9' high-above the earth. If you live in an apartment your out of luck OR they could abandon grounding for safety purposes. You can't choke the RF signal without destroying the lightning protection. Lightning is RF.

3. It would seem to me the best way would set an rf level that took into account distance from existing licensed stations and would be based on a simple to build resistance pad you would use with a communications receiver to set your output allowed. You would set the pad to the FCC set values (an internet table based on distance and power from licensed stations or maybe a programm that generates a circle of "pad" allowances around licensed transmitters), put the test setup 500' or so from your antenna, adjust receiver rf gain for say S7 thru the pad while listening to the licensed station, remove the pad into the antenna and then adjust your transmitter to register the same S7. No nighttime operation or suitable pad adjusted lowering of power. Online coordination for frequencies through non-profit groups like this, frequency sharing (just like in the twenties) where someone else wants to use the same frequency, (live programming gets priority). Part 15 operator responsible to check FCC site weekly for changes in licensed stations on the frequency and responsible to adjust parameters accordingly.
My idea makes maximum use of frequencies that maybe underused in some areas. It is based on comparison tests to the licensed stations that are easy as opposed to absolute values that are expensive and difficult to do. Different pad adjustment values could be based on transmitter quality. i.e. a type accepted transmitter or one tested by a licensed technician maybe allowed a higher pad value (more power).
I'm thinking power level to cover 2 mile radius max (best situation: no 1kw licensed station in 60 miles) to say power to cover 100 feet with station in same town within ten miles (which frequency you would never use anyway). etc... Any thoughts??