Go back and read Post # 10 where I talk about my OVER Transmitting Discovery.
This is not a small observation.
I have found that a single buried radial increases the signal of an AM station IN THE DIRECTION the radial is pointing!
Nothing like this has ever been said, EVEN THOUGH PART15.US HAS MORE CREDENTIALED RADIO ENGINEERS THAN ANY OTHER PART 15 WEBSITE!!
What this means is that when you ride down the street checking your range, you've got to go in a complete circumference around your transmitter, looking for HOT SPOTS where lobes reach out and give extra coverage in certain directions.
On the one hand someone might expect an evenly distributed circle of balanced ground radials with the 10-foot mast at the exact center to distribute a perfect circle of radiation, this can be off-set by whether it's on a hill, the surrounding obstructions, metals in the ground and over-head wires, and moistures as may be encountered.
The Part 15 experience has only begun, and we are here at the forefront!
The observation that the radial appears to direct the signal along the direction of the radial would be stronger if the test were repeated with either no radial or a radial in another direction. The reason is that other factors will affect the pattern, especially power lines and other wired utilities which can act as both transmitting and receiving antennas and which can distort the pattern measurements. There may be a combination of radiated and conducted RF signals and this could help to separate the two.
Neil
One part of Radio8Z's suggestions is already known, by simply recalling the days before the buried radial was added.
In those days no signal at all was going up the hill toward the south, and I once drove up to the south end of the block to find out whether some people I know up on that street might be able to listen, but there was NOTHING reaching up there.
Adding the ground radial up the hill was a major power boost.
Yes, so the next thing to try is a different buried ground wire pointing somewhere else. O.K. It's on the list!
I will do this test on the OTHER frequency, different transmitter, to make it an independent experiment. Coming this week!
Actually, one Sunday morning, I took my Field Intensity Meter (the same Nems Clarke unit I use for the commercial night directional station I work for, which is calibrated regularly and passes FCC inspection) and went around my town doing readings in all directions. Obviously I couldn't do every degree on the compass, and buildings and such prevented me from being at equal distances, but I thought it would be interesting anyway. I took reading in, I believe, 41 locations, most in town, a few a mile or so away.
My town is 1/2 mile long literally 4 blocks wide, with one loop to the north of new development. There's an adjacent town about a half mile away as well, and I went around there too.
I've been meaning to make up a map of town with the varying power levels recorded. It's clear that distance is not the only factor in signal travel -- which I knew, but it was intersting to see it. Our town is on a rather large hill, I'm near the top, and my transmitter/antenna is on the third floor outside window frame of my house so I've got pretty good height.
I noticed no real hot spots or powerful lobes while doing this. Quite a bit of variation, but nothing mid blowing.
Also, while doing these readings I also of course monitored on my car radio, and ALSO brought along a cheap, quite crummy $5 portable hand held transistor radio. In each place that I took readings, not only could I hear the station fine on the car radio, I could hear it fine on the crappy transistor radio, too. I didn't test into "fringe areas" because I wasn't that concerned how things were in spots where I was fading out. I took my readings on main street in my town, and the town next door, going block by block, to verify that both business districts could hear me OK, and also in all the residential spots. I can bea heard well any place where I need to be heard. Do get to where I lose it completely I'm out of the immediate inhabited area.
Impressed to discover that they're listening to my station in the City Clerks office in City Hall, the Library, and the coffee shop/antique store.
Might also be worth noting that I am indeed in Minnesota's "Iron Range" called that because there's a ton of iron in the soil here. If you drive around on dirt roads wyou wind up with red tires from the iron ore in the dirt. Might have something to do with ground conductivity.
This coming week I'm going to really try to remember to stop and take a reading with the FIM in the weird hot spot that's well out of town that I mentioned. it may not be all that hot, but it's quite a ways past where the signal fades out on the car radio, so suddently have it pop on for a couple seconds is weird!
We also need to remember that absorbind and reflecting of signals can play a major part. FCC takes this into account when someone applies to put up, say, a cell tower, within primary coverage of a directional AM, as their tower can affect the directional pattern of the AM and potentially cause interference. Same with other metal structures. Someone puts up a big metal pole building near our antenna array and we can see a difference. When little pine trees spring up on the land where our towers are it affects our pattern -- they suck down some signal -- we regularly have to hire someone to cut 'em down -- carefully to not damage the hundreds of buried radials at the site!
Tim in Bovey
Iron Range Country
Tim in Bovey brings up another idea for improving the ground characteristics of the relatively small area of a Part 15 ground radial installation...
We can add supplements to the earth, like a bag of iron dust, or start burying iron junk everywhere, then lay the copper radials on top of it all. We might write a whole new page of Part 15 history!
When Manteca Local Radio was in full swing, we found we were getting crazy range up and down hwy 99.. Like, really crazy. Remember the Sacramento range master the car dealer used that supposedly got ten miles? Well, it turns out we were sitting on an iron deposit that explained both my range and the range of the range master.. Funny how unintentional radiators work...
So, the past couple days I've tried to examine the loud signal phenomonon I get driging out of town every day.
It happens way out of what I consider my reception area. I can BARELY hear my signal there in the middle of the day, buried in static -- so it really jumps out at me when it comes booming in for a second.
I noticed this week that it happens when I go under power lines that cross over the highway at 90 degrees, at an intersectiion with a county road. Keep in mind this is prodably a couple miles from my antenna. There's a pole on each side of the divided 4 lane highway, and the power line continues off at an angle along the county road to the right and left. Oddly, the signal does NOT come in under the power lines along their route in ANY place except right over the 4 lane. If I turn off to the county road and pull into a driveway that puts me under that same power line, the signal does not change. Literally, it's ONLY in the section of power lines that goes over the 4 lane. The moment it passes over the highway and over the pole on either side, the signal vanishes! I followed the line down the country road in both directions and pulled off under when I had the chances and it never happened, except right under the line out on the main highway! How the heck the signal winds up radiating under that one section of highway is beyond me. Along the same highway heading home, I pass under other power lines none of which have this same phenomonon. And it's isolated to that one section that's as wide as the highway. Near as I can tell there are no transformers or other devices on the poles on either side of the highway - just insulators.
When I get a chance I'm going to take my FIM up there and see what the actual field strength jumps to when under the line at the highway. It's gotta be nearly immeasurable as soon as I'm 20 feet away from the line. But booming right under it! Crazy!
OH, and just for the heck of it, I looked at the map.. my water line ground points due east and the main water line that it connects to is nearly perfectly N/S and this line is about 2 miles away and almost perfectly southeast, so right between the grounds. Still seemed weird that there was no radiation - or reradiation anywhere else along that power line!
Tim in Bovey
Iron Range Country