I saw this from HB...
'The total length of the transmission line, antenna and ground lead (if used) shall not exceed 3 meters' This long wire is going to be considered a radiating element which creates an unbalanced dipole antenna.
Emphasis added.
This is obviously a topic with many facets. Concerning the use of the word "dipole" I wanted to ensure everyone knows that one of the Procaster or Rangemaster devices atop a tall post with ground wire to ground, is still a monopole (not a dipole) by definition since feeding a monopole (or dipole as well) is possible anywhere along the conductor without changing the primary definition of the antenna. Yeah it's still a longer than 9m monopole antenna, but a monopole nonetheless.
Regardless, if that radiating element (antenna + ground lead) is longer than 3 meters, you are not in strict compliance. To be honest, I wish we could all stop discussing this issue completely!
Regardless, if that radiating element (antenna + ground lead) is longer than 3 meters, you are not in strict compliance.
That's very true.
To be honest, I wish we could all stop discussing this issue completely!
That's how ostriches deal with such problems. Just pretend it's not there.
(Although it's just a myth that the reason they stick their head in the sand is because they think it's a way to avoid danger)
That's how ostriches deal with such problems. Just pretend it's not there.
(Although it's just a myth that the reason they stick their head in the sand is because they think it's a way to avoid danger)
In my case, I sometimes avoid talking about the ground lead issue because it's been discussed to death already, in just about every Part 15 forum; not because I'm pretending it's not there. How long are we supposed to keep talking about it? Further discussion is not going to provide clarification and/or general consent. If the FCC had really wanted, they could have included specific wording about radiation of power and audio cables in their regulations.
Thinking about it though, I think that if you have an elevated installation, and ensure that all wiring (audio and power cables, and ground lead, if you have one) conforms to the field strength limitation in 15.209, you'd be safe*. However, I don't think that an actual ground lead in an elevated installation would conform to such a strict limit. If you had no ground lead, and could install appropriate filtering in the power and audio cabling, you could achieve that. That would be an interesting experiment, to see what kind of range you'd get with such an install.
And there we go again, discussing the ground lead issue! 😆
*To do so, you'd need an accurate and calibrated field strength meter.
If you go by the field strength section not part 15.219 without the power or antenna/ground length restrictions it is puny like the Part 15 FM is. Even a Procaster without a ground is way better. Much better to go by 15.219 just with no ground if elevated. Timinbovey who used to post here has a Procaster on a pole with no ground at all just the 104" antenna it came with and gets 1/2 mile of good solid signal and I think he said can be heard up to a mile in a car.
And as mentioned since all transmitters are certified by 15.219 how are you going to know your field strength? And how do you explain this...24,000/fkHz μV/m@30meters? Yes that is the allowed field strength of 15.209. But that is not 24,000uV/M@30meters. That would be too good!
There's something else there. I can't find what that means. I think if I guess it means 24000 divided by the frequency so actual field strength at 1630 kLz would be 24000 divided by 1630 = 14.72uV/M@ 30 meters!! That's worse than FM part 15! That will get you to the curb on a residential street. Maybe not with a typical radio. And only in the daytime.
Consider this...even the GE super radio has a stated sensitivity of 65uV/M for a "listenable" station. Better than all radios. Just how far do you think the FCC field strength for AM will get you? Even with a car, 20 ft?!!
@rugster The ground lead discussion never goes away because it has always remained unresolved. At face value it's clear, but then you have the TH and all its predecessors that were certified to be grounded via your wall receptacles which appears to violate the 3meter limit just as much as an elevated install.
I do get your point though, when is enough enough? Theres no resolve to it, so what's the point? So I get why you'd want to ignore it. However, I disagree with readily trying to discourage the topic from being mentioned or nipping it in the bud when it comes up.
...like HB does.
And as mentioned since all transmitters are certified by 15.219 how are you going to know your field strength?
That's just it, you dont need to know, its irrelevant to it's compliant operation.
The FCC created the alternate rule in 1956 for the benefit of kids, because it was such a major hobby but neither the kids nor the general public had any means of measuring field strength, so the FCC created the 10ft 200mw rule...
Ironically it was a manufactured part 15 transmitter at the time happened to be under investigation by the FTC for false claims -- it did not perform well at all - the FTC called in the FCC to confirm that it did not perform as advertised, which the FCC did. However, the AM walkie-talkie (Radio-Vox) included instructions and adapters for connecting to things like box spring mattresses and car antennas - using those methods increased range considerably and made it noncompliant..
It was because of the FCCs test of those units that made them reconsider the 200mw input and reduce it by half to 100mw...
If not for the Radio-Vox false advertising in the mid 50s, we would have a 200mw input today!
If you go by the field strength section not part 15.219 without the power or antenna/ground length restrictions it is puny like the Part 15 FM is. Even a Procaster without a ground is way better. Much better to go by 15.219 just with no ground if elevated. Timinbovey who used to post here has a Procaster on a pole with no ground at all just the 104" antenna it came with and gets 1/2 mile of good solid signal and I think he said can be heard up to a mile in a car.
And as mentioned since all transmitters are certified by 15.219 how are you going to know your field strength? And how do you explain this...24,000/fkHz μV/m@30meters? Yes that is the allowed field strength of 15.209. But that is not 24,000uV/M@30meters. That would be too good!
There's something else there. I can't find what that means. I think if I guess it means 24000 divided by the frequency so actual field strength at 1630 kLz would be 24000 divided by 1630 = 14.72uV/M@ 30 meters!! That's worse than FM part 15! That will get you to the curb on a residential street. Maybe not with a typical radio. And only in the daytime.
Consider this...even the GE super radio has a stated sensitivity of 65uV/M for a "listenable" station. Better than all radios. Just how far do you think the FCC field strength for AM will get you? Even with a car, 20 ft?!!
You're misunderstanding what I meant @mark. Perhaps I wasn't clear in my explanation. I wasn't referring to the total radiation from the transmitter conforming to FCC 15.209, I was talking about just the power and audio cables - not the antenna. One of the points of contention with elevated installations has long been the belief/conviction by some that if an elevated installation with no ground lead has good coverage, it must be because the ground and/or audio cables are radiating. My point was, that if you have an elevated installation with no ground lead, and ensure that the audio and power cables are not radiating any more than what is allowed by 15.209, you should be pretty safe. Admittedly, even with an accurate FS meter, it could be difficult to discern whether the field strength around one of the cables is coming from the cable, or from the antenna, but I think you could get a pretty good idea. Just a thought, and I might be mistaken.
Yes, as you said, the allowed field strength under 15.209 is very low. Your calculation is correct.
I'm well familiar with Tim's installation - or at least, his description of it online. I sure wish I lived in that part of the country. I'd be interested to hear his station for myself, to gauge the coverage. I have long been curious about his installation without a ground lead, and how it achieves good coverage, as my Rangemaster at about 20 feet without a ground lead has not been doing quite so well. There is some partial obstruction by roofs and buildings though, which could explain it.
@rugster The ground lead discussion never goes away because it has always remained unresolved. At face value it's clear, but then you have the TH and all its predecessors that were certified to be grounded via your wall receptacles which appears to violate the 3meter limit just as much as an elevated install.
I do get your point though, when is enough enough? Theres no resolve to it, so what's the point? So I get why you'd want to ignore it. However, I disagree with readily trying to discourage the topic from being mentioned or nipping it in the bud when it comes up.
I completely see your point about it never having been resolved @richpowers. The TH is truly a head-scratcher. Inherent in it's design is that the AC wiring radiates, yet it was certified! I think we all remember the case of the feller who was using a TH in his house, unmodified, and exactly the way it was supposed to be used, yet was still cited, and his TH confiscated.
I hope I didn't come across as wanting to quash any discussion of this. It's just that sometimes, it seems as if we're going round in circles with this topic - because we are! 😆
I'm well familiar with Tim's installation - or at least, his description of it online. I sure wish I lived in that part of the country. I'd be interested to hear his station for myself, to gauge the coverage. I have long been curious about his installation without a ground lead, and how it achieves good coverage, as my Rangemaster at about 20 feet without a ground lead has not been doing quite so well. There is some partial obstruction by roofs and buildings though, which could explain it.
Talking of Part 15 stations with good coverage, a new Part 15 station recently came on the air a few miles from where I live, in the city of Alameda, CA. It is a relay station for Radio Sausalito, and broadcasts on 1570KHz. I spent a long afternoon in November, walking round the island of Alameda, checking the coverage, and was quite impressed. I made a fairly lengthy post about it, with a coverage map, over at HFU. I think I might replicate the post here, as I think it's a good example of the kind of coverage a good Part 15 installation can achieve. I am very curious to see the installation, or at least to learn some more details about it. It's on my list of things to do!
... The TH is truly a head-scratcher. Inherent in it's design is that the AC wiring radiates, yet it was certified! I think we all remember the case of the feller who was using a TH in his house, unmodified, and exactly the way it was supposed to be used, yet was still cited, and his TH confiscated.
The TH design was directly based on the Realty Radio transmitters (New Pilot Communications), but thosee weren't the only two certified part 15 AM transmiitters that used the. Wall receptacles for ground. The Amcast did too as did the forgetthename off the top of my head. But anyway there were no less than 4 certified part 15 AM transmitters on the market during the 1980s (when the TH were originally certified) that utilized ground in the same way. It was definently a common method used by most certified p15 transmitters..
And the story you refer to was not installed in a house but an old 8-story apartment building. The feild strength shown in the NOUO was quite extreme.
@rugster Sorry about the misunderstanding of what you were referring too with the field strength.
Really I think it's quite simple and very straight forward about all this with ground leads. For example, the Procaster comes with a stock 104" antenna(2.6 meters) to leave some room for a "ground lead"
You have 0.4 meters left(1.3 ft)...a bit over 15 inches for a ground lead so the transmitter basically has to mounted on the ground if you have a underground ground system as 15 inches only can be above ground. If you put the transmitter elsewhere like a roof and use the metal eavestrough as a "ground" that metal eavestrough now is a large conductor and is considered a ground lead. Same with it being on a pole. If you connect the "ground lead" to a metal pole and the pole is on a fence 5 ft above ground the pole now adds to the ground lead as it's a metal conductor unless it is wood.
The only one "if" here is if you use an elevated ground like a metal eavestrough around the roof is it considered a ground lead if it's not going to ground? Is that a loophole in the rule?
That's the only grey area to this. And if a ground lead isn't actually going to ground is it making that much of a difference in radiated signal. I think since audio cables are not included in the rules using no ground at all the audio cables are doing just the same thing as an elevated ground would. So simple, if the transmitter is not going to be mounted a bit more than a foot off ground and you are going to stick it up on a pole just use no ground at all. The audio cables and the cable supplying power will act as a "ground" and the transmitter will get the ground from the electrical ground in your house.
A long time ago someone was talking about dumping truckloads of dirt in his backyard till he had a 30ft hill than driving his ground rod into that.. Don't think he was serious. Another had the idea of using 30ft of PVC pipe filled with dirt, guess you'd need guy wires for that.
To be honest, I wish we could all stop discussing this issue completely!
I understand. Just so everyone is clear, I run an antenna design and analysis department (for USG). We've been troubled by what appears to be inconsistent interpretation of 15.219 by the various field offices of the FCC. This has implications for similar 15.217 as well. We're running a couple of certified LPAM transmitters above a short field of radials plus a ground rod and evaluating field strengths. Based on what I'm reading here and elsewhere we might try elevating the system with and without chokes (Type 75 most likely) on the "ground" and audio/power leads.
I read on another forum something about FCC inspection interprets the length limit as electrical rather than physical length. That point sounded the alarm for us and will be analyzed.
Anyway, fun stuff.