OK, that makes a lot more sense. Thanks Rich.
The field intensity at 100 meters with an antenna 10 meters high would be 5uv worst case according to that graph - definitely listenable by a good car receiver and even a good portable. Even at 200 meters (about 650 feet) it would be listenable on a good car receiver (assuming that the field intensity is inversely proportional out that far). That ties in with my real world experiences, where I had the transmitter mounted on a rooftop of a 3+ story building (on a hilltop, so relative to the ground in front of it, the antenna was even higher).
I was beginning to wonder how I got such good results with that elevated transmitter, when with essentially a ground mounted antenna now I'm not getting nearly that (closer to 200 meters with Canadian BETS rules). Amazing that antenna elevation makes so much of a difference (although we're really dealing with very small absolute differences - it's the relative difference that's so amazing).
Almost makes me wonder what the second story would give me. But it could make some sense why some are reporting such good range with their part 15 FM transmitters. One way would be to bluetooth an audio signal to the transmitter and have it in a high place. Or maybe get some really good shielded audio cable and have it linked to a transmitter way up in an attic. This could get closer to that 1 mile range. Even AM would be some improvement and worth the experiment.
The field intensity at 100 meters with an antenna 10 meters high would be 5uv worst case according to that graph - definitely listenable by a good car receiver and even a good portable. Even at 200 meters (about 650 feet) it would be listenable on a good car receiver (assuming that the field intensity is inversely proportional out that far).
Just to note that the field intensity at 200 meters for a transmit antenna elevated 10 meters above level terrain will not be attenuated from the field at 100 meters only by inverse distance -- just as it was not attenuated exactly by the inverse distance between the field at 3 meters and the field at 100 meters.
IOW, the difference between the NEC field shown at 100 meters would not be reduced to exactly 1/2 for a 200 meter terrestrial path.
Perhaps Rich can confirm this.
I think what I'm seeing in the graph is antenna elevation on the y axis, field strength on the x axis. The red curve is the field strength at 3 meters horizontal varying with antenna height. The blue curve is the field strength at 100 meters horizontal, again varying with antenna height.
So that means that with an elevation of 5 meters, the field strength at 100 meters horizontal would be 10uv/m? It goes up a bit more with increasing elevation, and then seems to settle back down to 10uv/m at 10 meters elevation.
If that is correct, it would be interesting for Tim to test out elevations of 2.8 meters and 5 meters (if he can) to get the actual readings. 5 meters is about 16 feet 5 inches. I'm not sure how that could be done - a really big fiberglass ladder? Even if 5 meters isn't possible, perhaps 4 or somewhere around there (i.e., at least 2 sets of readings with different antenna elevations).
I think what I'm seeing in the graph is antenna elevation on the y axis, field strength on the x axis. etc.
AR -
The plots in my reply #28 show the field intensities existing at elevations between zero and 10 meters above level terrain for 5 mS/m earth conductivity (average), and at horizontal distances of 3 and 100 meters from a vertically-polarized, 1/2-wave dipole transmit antenna with a FIXED radiation center elevation of 10 meters AGL -- and which radiates a maximum field of exactly 250 µV/m in free space.
Ahhhhhh...
Finally, illumination. Thanks. So the elevation of the receive antenna matters as well, which I should have realized in the first place.
Yeah - I've got serious eye issues, too
-but if I blow it way up on the computer
screen...
I always wanted to be a real RF engineer.
I started out in EE but couldn't keep up.
Anyway this is fun. Thanks Rich.
Brooce, WLP
TheLegacy, we talked a bit at the ALPB Meeting about your cramped frequency problem on 96.3, which you mention again in Post # 30 up above.
I said I would do a frequency search of your area using radio-locater, and I've found several FM channels that might be better than 96.3.
Check these out and tell me what you find:
92.5
101.7
101.9
103.3
106.3
106.5
107.3.
Hope it helps.
92.5 Was one I thought about, but at night thee is a LOUD God caster that comes in louder than the country station. 107.3 Has the translator for the God Caster @ 88.3 Mhz which the translator is in VA and I don't know why its on air.
106.3 won't work because its close to the station that comes in on 106.5.
101.7 and 101.9 I'll have to look at during the night again I can't remember what was wrong with those. I'll have to look at them again. I can't remember 103.3 either but I'll check with it as well. I remember looking at Radio Locator for frequencies as well as did a scan but it don't hurt to try again when things get heated and I have to sign off. I'm also looking now to be sure those AM frequencies are clear as well. But as I said every night the band is always open and from what I've seen no room for broadcasting at night on FM.
103.3 Pop Station Comes In Loud
101.7 Used comes in quite good.
Actually some of those frequencies were having signals louder than 96.3 And Tonight 96.3 had on and off inversion tht made the Morehead City station come in.
TheLegacy I now have a clear picture that you are swamped in FM signals, just like you've been saying.
I suspect, and of course don't actually know, but I suspect that your location where you are monitoring is on high ground, up above average terrain. That exposes a listener to far more intense activity than someone down in a bowl or valley, which is my situation.
I am surrounded on all sides by uphill and that gives me a realtively quieter FM band than a neighbor up on the summit of the hill who had great difficulty finding an open frequency for a C.Crane FM transmitter.
The converse is true, however... being up high gives you an extreme advantage for transmitting over a wider area.
My FM transmissions sort of fill in the bottom of this bowl, but do not tend to continue up the hills.
The house is on a slight hill itself. I'm thinking of putting the AM transmitter upstairs if I can when my room mate moves out. However at the moment i'm actually on the first floor. Its just a good area and the house is wood. I'm also just being extra carefull to not interfere with a listener who would want to hear the country station when it does come in here as some already mentioned to my Wife. They don't have an issue with me running the station when the country station doesn't come in. But that one time I forget or the inversion catches me off guard could not be cool for me. That is what NOUO's are made of. I'm still saving with bated breath for the AM transmitter. I'll probably just go off the air on FM after 6 so I don't have to keep checking. It will be better for the listeners too as they won't have to hear the station go off every hour or 1/2 hour to check.