in that case it sounds like a lot of the part 15 rules come down to the personal discretion of your local fcc inspector.
while were on the topic of rules and regulations, what exactly are the rules for on campus broadcasting? as i understand it, on university campuses you can have a slightly higher power output. is this correct?
15.221 alows a maximum field strengt of 15uV/m at one radianlength (about 100 feet near the upper end of the AM BCB) from any border of the campus. Unless the campus is very,very large, the usual 15.219 rules give more range.
For my Talking House ATU antenna, I'm using 6 wire radials about 12 feet long evenly spaced around the base of the antenna.
The antenna is on the roof.
oh wow i didn't realize the campus rules were so restrictive. i am a college student and was hoping that i would be able to run slightly larger experiments on campus. never mind that idea.
back to radials..
i just got a look at the roof of my studio where i plan to setup my radio tomorrow. it looks like the roof is made of tin or some other metal sheeting covered with tar paper. is that going to be problematic? could i just connect my transmitter's ground to some exposed part of the metal roof and use it as a ground plane or would it be better if i used wire radials? if i use wire radials, do i want to short them to the roof or should they be isolated from it?
"I'd imagine coils are allowed because they would be too difficult to measure, but the vertical height of the coil is counted as part of the total length of the antenna."
Well, that could be countered as well. If the coil is mounted horizontally in a rainproof cabinet, like the one Carl's guest Brian on the latest LPH has, with a tuning stylus and all, it could be considered a type of ATU, and not part of the antenna proper. The antenna apparently doesn't care if the coil is horizontal or vertical.
hmm. i just put my transmitter up on top of a two story building. range was not really improved much. i still only get about 75m. i am grounding the transmitter by attaching onto the electrical conduit that runs all over the roof. is that a bad way to setup a ground plane?
That will not produce the RF ground effect you want. They should be radials, a bunch of them, about the base and center of the antenna mount, just as MRAM has indicated for his system. If your metal conduit is somehow grounded to actual Earth, then bonding the set of radials to it might (I say 'might') work for you, provided there is no loop effect that could goof up your audio.
Generally, more radials are better. However, for a 10' antenna, I think more than 12 or 16 at 20' each would be entering an area of diminishing returns. What you want is enough to cover a reasonable portion of the near field. We concentrate there for broadcast frequencies above, say, 1600 kHz, because the higher BCB frequencies are more efficient for loading coils (more inductance with fewer turns, less resistance) and generate most field strength within about .17 wavelength. With no decent return (through the air) to ground, it will dissipate quickly after that.
To contrast, loading with a coil at low frequencies requires many more turns to get good inductance, you sacrifice with more resistance in the coil, and so less power ... IOW, it isn't as efficient. However, the near field at low BCB frequencies has a much larger near field, so, though it starts out much weaker, it remains with whatever it has for longer distance, i.e., the transition from near field to far field starts to lose definition ... it just fades away. But at these miniscule power levels, penetration is poor in the lower part of the band, so you won't get much anyway.
Most of the successful range attributes of inductance coil loaded antenna systems I've seen here as used with SSTRAN have been in the upper portion of the band with a good set of ground radials bonded to Earth with multiple ground rods.
A roof-mounted system only has the advantage of getting over buildings. Otherwise, AM radio travels by ground wave during the day, so the best ground system you can get is vital.
3 basic things, then:
1) Maximum loading on an empty frequency in the uppermost portion of the BCB.
2) Maximun resonance, which requires patient matching for most field strength.
3) Maximum RF ground.
These 3 all affect each other, so finding a balance that works for you is where your brains and elbow grease come together 😉
That will not produce the RF ground effect you want. They should be radials about the base of the antenna and coil, just as MRAM has indicated for his system, although I'd make at least 12, and as long as you can fit on your roof. If your metal conduit is somehow grounded to actual Earth, then bonding the set of radials to it might (I say 'might') work for you, provided there is no loop effect that could goof up your audio.
What you're trying to do is make a ground radial system to cover as much of the near field (approx .17 wavelength) as you can for the upper portion of the BCB.
How are you tuning your system to resonance? What are you measuring with?
You must tap the coil properly. Do not modulate (no audio). It isn't always easy, sometimes you get a false reading at an overtone frequency. After you max that out, you have to fine tune by changing the length of the antenna by moving it up and down in the slotted lower section until you get it to peak. I did mine at 1/4" intervals ... took a long time. Ended up where one Sharpie penline width made a difference.
3 basic things, then:
1) Maximum loading on an empty frequency in the uppermost portion of the BCB.
2) Maximun resonance, which requires patient matching for most field strength.
3) Maximum RF ground.
These 3 all affect each other, so finding a balance that works for you is where your brains and elbow grease come together 😉
thanks for the advice ken. i have a fluke 117 multimeter that i am using to check the tuning. i'm pretty confident that i tuned the resonance properly i got it set to exactly 13v with no modulation.
would grounding into my building's electrical system in addition to having a radial setup have a negative effect on the radial pattern? is the goal to have as much grounded metal as possible or to have a specific size and pattern under the antenna?
unfortunately i am in a city and my building doesn't have any grass/soil around it. any ideas on some other way to get to earth ground or to simulate it? what about an 'artificial ground plane' for cb radio?
heres a little update on my amt3000. i took it back to my house and set it up on my roof. i found a100ft length of 16awg copper wire, stripped it at the center point, and draped over either side of my roof. i used an alligator clip to connect the center point to my transmitter's ground. i tuned up the coil and got it to peak at 13V on the dime. walking around my neighborhood with a digital receiver i was able to hear it decently at 300m after which is cut out pretty fast. listening in my car i was able to get 600m away before it cut out!
i went to home depot and bought an 8ft grounding rod. on my way home i wasn't able to pick up the signal until right outside my house. i checked the voltage and it was down to 3.5V! i tried retuning it but haven't been able to get it past 3.5V.
any ideas what might of happened? it was pretty hot out today (around 87F) and the transmitter was in direct sunlight. might that have done something?
on the plus side i just finished hammering in a ground rod in my backyard so hopefully once i get the transmitter tuned up properly i will get an improved range.
i noticed that when i moved my ground radial around i would get different maximum voltages. this led me to go ahead and make a proper radial setup with 8 radials: 
disconnected from the grounding rod i am back up to 10.5V peak. its still not as good as when i had one giant radial hanging over the side of my house (13V) but it is a start. i tried attaching the radial system back to the ground rod and my max voltage dropped back down to 3.5V. are you guys sure i should be using a grounding rod?
A ground rod is for Earth ground, i.e., into the soil. That's what was meant ... the transmitter and antenna system close to the ground, not on a roof. Being on a roof helps only with getting over buildings, but that's countered with the fact that daytime AM BCB travels by ground wave. You can get ground wave from a roof, but it still has to have good ground.
It's hard to get a good ground connection on a roof ... it would have to be some sort of metal plumbing pipe which goes into the ground ... and not PVC. As soon as a metal plumbing pipe is connected to PVC pipes above ground, you lose its ground properties.
You're 'giant radial' is just a wire, right? Well. if it's connected above ground to the ground side of the TX and hanging down the side of the house, as you say, it then becomes a dipole where the ground wire is doing as much or more than the antenna. The combination, above ground, constitutes a much longer total radiating system. The connection to ground for an SSTRAN can't be more than a few inches in an above ground system. Otherwise, again, it becomes part of the radiating system, more than the allowable 10' ... and is illegal.
But that's why you were seeing larger numbers.
Any number of folks here have pulled down their roof-mounted systems and went with a ground-mounted system with buried radials directly under the TX-antenna, and got better performance.
Also, you should be aware of the time-of-day. Lots of ionospheric RFI appears at and after sundown.
oh wow, do all above ground radials act as part of the antenna? i've seen lots of people talking about having sets of above ground radials on their roofs in these forums (including mram1500 in this very thread).
in my previous post i have an image of 8 radials around my antenna on my roof. would that setup be acting as part of the antenna?
Although there are differing opinions as to how the FCC views radials above ground, when properly deployed radials do not radiate. They do increase the efficiency of the antenna system which the end result is more signal radiated.
The efficiency is improved simply because the radials reduce ground loss. Less signal lost in the ground-more signal radiated.
"The efficiency is improved simply because the radials reduce ground loss. Less signal lost in the ground-more signal radiated."
Right, just so ... but I cannot see how draping a wire across the roof and vertically down a wall could be considered a ground radial. Putting some wires radiating outwards from the base of the antenna flat on the roof (don't go down any walls) would be much more like it, to prevent ground loss, but IMO even that should be attached to Earth ground in some way.
Otherwise, the ground of a wall wart or audio cable shield would have to do ... inadequate for safety IMO.
The only way I can think of would be a metal vent pipe, which would be in a very old building, and might still be modified, i.e., corroded sections replaced with PVC, before it goes Earth, rendering it useless as a ground path.
Cap hats are, AFAIK, also considered part of the antenna, same as above ground radials, but as you say, these things are still up for debate.
Anyway, don't let any of that stop experimentation ... it's where we all learn.