I can't find it again now but somewhere in the midst of a discussion embed kind of deep between two guys at https://m.facebook.com/groups/part15broadcasters / was some comments made that I just had to reply to last night.. but my comments weren't accepted because I am not meeting some kind of "criteria"... I don't understand or care enough to try and figure out why my post aren't being accepted because I so seldom use Facebook anyway, but I do still have the couple excerpts from his rather long post that I wanted to reply too..
Here's what he said (after detailing his own experience in the broadcast industry and engineering and so forth). The discussion was a few months ago and related to the "Delete Delete Delete" hearings..
"...Also, another point that you need to be made aware of. The United States Title 47 CFR Part 15 Rules can't be dramatically changed because the United States has treaty negotiations with Canada and Mexico that go many years back, some litterly to the 40s and 50s. The Part 15 rules were slightly modified in 1990 because the Internet and Cellular technology was here at that time. Nothing was changed in the rules for unlicensed broadcasting on the AM and FM bands."
I'm still sure what to think about that comment but it kind of sounds like nonsense to me, but maybe it has some legitimacy - but I really think he was just spewing vague speculations.
He goes on...
"Finally, the "one thing" I have been looking into which is a *slight modification* in Part 15.219 of the AM rules is doing something about relaxing the "ground lead" rule. For example, owners of the Hamilton Rangemaster and Chez Procaster should be allowed to have a longer ground lead from the transmitter with a copper wire (i.e. 20 to 30 feet) from the transmitter mounted on a pole with the copper wire running to a ground rod that is buried 8 feet into the ground. The Part 15.219 rule doesn't accommodate this and I know why. When that rule was written, the engineering and technology section of the FCC sees that copper wire as a part of the antenna system, which yes it is. However, it doesn't radiate enough in field strength to cause interference."
Not sure what he meant by "it doesn't radiate enough in field strength to cause interference". But it is obviously clear that the field strength is going to increase in proportion to the length of the lead (aka: antenna). So I don't really understand what point he was trying to illustrate. But then it really gets good when he laid down this gem:
"Ground conductivity shouldn't be taken into a consideration as a factor in gaining field strength. The power output of the transmitter will remain at 100 milliwatts."
How much more nonsense can he dish out? We all know, the limit is 100mw input to the final stage, there's no limit on output with 15.219, and that output capability directly corresponds with the ground conductivity of the area. In fact the ground conductivity is probably more important than the length of antenna itself (and/or ground lead).
I can't help but wonder how many on Facebook thought this guy knew what he was talking about? No one seemed to question his expertise on these matters
About the treaties with Canada US and Mexico, there is but it's for crossborder RF from commercial stations so a blaster from Toronto can't wipe out a station in Buffalo or a Mexican station can't interfere with a local Texas station and a USA station can't do the same to those countries. Frequency selection has to take that into consideration but how this affects part 15? Don't think it does. But what if a part 15 AM station was set up right across the border from Canada where one side of the street was USA and the other side Canada and there's several areas like that even at Niagara Falls, and that part 15 station while legal in the USA is interfering with a station across the border could Canada not apply the treaty?
Don't know, just creating a situation for discussion. As for the treaty having anything to do with part 15 rules or changing them I don't think so.
As for the longer ground leads radiating more and if they do radiate more or not is easily determined with an Potomac FIM 21 field strength meter that covers the 535kz to 1710kz AM band. Why hasn't someone done this? Set up a Procaster with 3 meter antenna, measure field strength at say 30 meters away and then add lengths of ground lead and see what happens. Wonder if Bill at HB has done this? He had the AM field strength meter to do the AM transmitter challenge. This would answer the debate that has gone on for ages.
As for ground conductivity not mattering....I guess he knows more than the engineers that manufacture the transmitters.
. But what if a part 15 AM station was set up right across the border from Canada where one side of the street was USA and the other side Canada and there's several areas like that even at Niagara Falls, and that part 15 station while legal in the USA is interfering with a station across the border could Canada not apply the treaty?
Well there has been one for over 55 years, the Detroit-Windsor tunnel radio. It actually crosses underwater but it's still a part 15 station.
As for the longer ground leads radiating more and if they do radiate more or not is easily determined with an Potomac FIM 21 field strength meter that covers the 535kz to 1710kz AM band. Why hasn't someone done this?
Are you seriously suggesting that extending the lead does not directly result in an increase of field strength?
@richpowers I am not suggesting anything. I'm just thinking out loud that whether it does and how much different lengths of ground leads would affect radiated signal could easily be seen with a FIM 21. All other things being equal e.g. the same ground system, antenna and location.
@mark All can be calculated using laws of physics (not by me of course).
Here is an excerpt of an old R. Fry post (and charts) many years ago...
"... .. The conductor lengths were chosen to cover the range of systems from one fully compliant with FCC §15.219(b) to those where the transmitter and whip are elevated up to 10 meters (32.8 feet) above the earth. A standard 8-foot long ground rod was used. The length of the whip antenna was 102 inches. Earth conductivity was set to "average." ... ....
The field improvement at 1 mile for the system shown in the chart at 10-meter elevation is better than 5:1 compared to the system using only a 0.4-meter conductor length to the ground rod.
The system at zero elevation would need more than 25 times that 90 mW transmitter power to produce the same ~ 170 µV/m field at 1 mile as the system elevated 10 meters. ... ..."
Full post at: https://www.part15.org/community/temp/define-ground-lead/paged/2/#pos
t-30914
@richpowers Ok so it has been done! Field strength was measured with different ground lead lengths so the evidence is there. I didn't know that had been done to prove it. So the poster at Facebook forum is incorrect that it won't make much difference if you have the transmitter on a pole and extend the lead to the ground.
@mark That is true, as far as it goes. But earlier in the thread, @richpowers states that ground conductivity as a factor far exceeds the length of the antenna factor.
I would have to agree. When I was located on Bowen Island, essentially a rock sticking out of the ocean (so lousy ground conductivity), I had an AM transmitter mounted at about 25 feet, with a correspondingly long ground lead to radials. I never could get more than about 1/4 mile range.
In the community where I now reside, which lies on a flood plain (so great ground conductivity), I was able to get 1-2 miles range with that same transmitter mounted a few feet above soil, and grounded to the metal pipe that I had pounded in about 6 feet or so.
The length of the antenna and ground was overshadowed by the huge changes in ground conductivity. Kind of makes you think about whether the limitations on antennas with AM are really necessary, as environmental factors make much more of a difference.
Somewhere, I recently saw R Fry (I think it may be earlier in the same above linked thread) also calculated differences in lengths of the ground rods themselves (how deep they're buried), 3ft, 4ft, 5,ft etc. and it apparently makes a difference in field strength too.
You know.. We should compile all his chart and graph "paper blizzards" (that we use to mock him about 20 years ago when we all despised him). For a guy who most of us originally considered as an enemy of the hobby, he actually turned out to be quite possibly the most valuable individual (so far as reliable and accurate technical information) that's ever been on this forum.
I use to almost HATE him, but over the decades I turned to admire him. Wish he were still here
There's numerous people I wish were still here.