I have been involved in a discussion on the Part 15 AM & FM Facebook group which was comparing the Rangemaster to the ProCaster. During this discussion, several individuals were claiming what seems to me to be exorbitant ranges for stock ProCaster transmitters (over 3 miles), supposedly installed 'close to' the ground.
Also recently Station8 is claiming over 4 miles range with a new antenna design.
Now, range is always directly proportional to the field strength generated by a transmitter/antenna combination. We are lucky in that Part 15.219 does not specify a maximum field strength (unlike FM, which is governed by 15.239), but instead places restrictions on the antenna system (no more than 3 meters in length, including feedline and ground wire) and no more than 100mw input to the final stage of the transmitter.
So there are things you can do to increase your field strrength within those guidelines, and therefore your range. You can improve the efficiency of the final stage of the transmitter (as SSTran claims with the AMT5000). Or you can improve your antenna system, as Station8 claims he has done.
That got me thinking as to what could be the maximum possible range for a Part 15 AM system.
I know that Rich has in the past calculated the field strength for a strictly legal ground installed transmitter using a monopole antenna with the NEC software. And I know that he also calculated that field strength with an elevated install and a long ground wire (I can't remember the exact length).
But do you think that I could find them? The search function on the website doesn't appear to be functioning at all (at least for me). So I was wondering if anyone (including Rich) has those graphs generated by NEC 4.2 handy.
I'm not going to get into it with those who are claiming huge range - there's really no point to that. I just want this information for my own musings.
We also have been told that the Station8 antenna is end fed and high gain. To get that kind of distance I suspect that it has to be directional (and I'm going to ask him that). Unfortunately, until we know more about the antenna, there is no way that it can be modelled.
Artisan Radio, you are a very welcome thinker on Part 15 affairs, despite being over the border in Canada where Part 15 does not apply. That actually makes it extra special because your viewpoint is unbiased.
The mystery of performance comparisons among Part 15 devices is what it's all about.
Because there are so many physical variables that shift with time, we can never expect to pin down exact numbers.
Also, regardless of claims that physics has limits established in the 1930s, new inventions are still popping up and inventors have not abandoned the quest for improvements.
We are also fortunate to have Station8 busy working on themes and variatons intended to extend the Part 15 range while maintaining current rules.
Keep in mind that debunkers and nay sayers are sometimes people who start by discrediting a new invention, and end up claiming ownership of that invention to fulfill a frustrated inability to invent anything on their own.
I was wondering if anyone (including Rich) has those graphs generated by NEC 4.2 handy.
Yes (see the graphic below).
Note that the groundwave field intensity at 1 mile when using a vertical ground lead length of 10 meters is about 5.7X greater than when/if that particular transmit system just exactly complied with FCC §15.219, for those conditions.
Given this reality, the general popularity and support of such long, radiating "ground" conductors on some Internet boards is easy to understand, if not legitimate.
[EDIT removed text to make thread easier to follow.]
To be fair, Carl, I did talk about how some individuals on other sites were discussing ranges that I felt were longer than possible with a compliant system.
I don't know how difficult it is to generate these graphs, but I was wondering if it would be possible to do something similar for distances of 1.5, 2, 3 etc. miles. I'm just trying to get a handle on what might be the maximum range, ignoring the legality of a long ground lead.
By the way, Rich, I am thinking of purchasing the NEC 4.2 software for my own personal use (not only for Part 15 but for amateur radio use). I've done some searches but can't seem to find a supplier - do you have any suggestions?
And thanks for producing that last graph in record time.
There are an infinite number of answers to that question depending on system configuration, adjustment, and the propagation/receiving environments.
But below is a NEC4.2 analysis for the conditions shown for what might be described as a better-than-average system that is compliant with FCC §15.219.
The fields shown in the graph may or may not be very useful over that 1- to 4-mile range, depending on the sensitivity of the receive system, and the local r-f noise level at the receive site.
NEC2 software is available from several sources, and in some cases it is free. Two of the free ones are EZNEC and 4nec2. There is a definite learning curve for them, as NEC models must conform to the standards that the software requires. 4nec2 has better graphing capabilities than EZNEC.
NEC2 cannot model antenna systems with buried conductors, such as those using radial ground systems and/or ground rods. That requires NEC4, which is available from its authors at Lawrence-Livermore Laboratory in California. Its cost for non-commercial use is about $300.
The NEC4 calculating "engine" can be used with either EZNEC or 4nec2.
My experience has shown that when people make claims for range there are always an infinite number of variables, none of which are accounted for or documented in the range.
Do they ever say things like "I got three miles range with my Rangecaster" and then say "but only in two directions when I was at the top of the hill and it was at least two hours before sunset and only in our car that has the really good radio with the antenna up all the way". No.
Generally when people are comparing two transmitters they NEVER compare them in identical condtions. Nor do they generally have each device installed in the particular arrangement that works to the best results with that particular transmitter.
Further the range will vary based on a milion other things, like frequency choosen, noise floor at that receiving area, modulation potential, and on and on.
You absolutely, positively, cannot declare range by listening on a radio. Unless every person you expect to listed has the same radio. Or the same car (and don't mind sitting in a parked car to listen).
I can assure you that my transmitter, if you could transplant the exact same conditions from my location here to, say inner city Minneapolis the range would drop dramatically simply due to the building density and ambient noise and interference.
A transmitter at 80% modulation has less range than one at 125% modulation. So you need the correct processing to make this happen.
There have been extremely rare occasions (like once or twice in 2 1/2 years) where I can hear my station at the stoplights on the east side of Grand Rapids which is 7 miles from my transmitter. It's weak. And it's noisy. But I can hear it and recognize songs. But I never try to tell anyone I have a 7 mile range. Many people will.
I get a solid 7100 feet out. Every single day, as long as the sun is up. That's about a mile and a half. So that makes a nearly 3 mile circle, doesn't it. Again, I consider the low noise floor and lack of interference here to be my one huge advantage. That and that the built in processing in the Procaster has no trouble modulating to 125% positive while avoiding over 100% negative.
I would not expect to tell others that they can expect the same range as me. They'd have to be in a tiny town away from noise. I'm also surrounded by crisp, clean Minnesota air. BTW it's 25 degrees, the wind has been gusting to 40 all day, and it's snowing.
TIB
Until the part about snowing.....turned me off there! 60 degrees and sunny here in Toronto.
Mark
The maximum range depends on how much effort someone wants to put into it. If the person is going to put the largest buried radial field they can on their property they will get near optimal results. On the other hand, if the person is going to put up a Talking House in a room indoors with the wire antenna straight from floor to ceiling and 2’ of the antenna running along the ceiling, they are not going to get optimal results.
Local ground conductivity is also a factor. https://www.fcc.gov/encyclopedia/m3-map-effective-ground-conductivity-united-states-wall-sized-map-am-broadcast-stations
I live in a region with a ground conductivity of 2. If I moved my exact install to a region with better ground conductivity, I would get much better range.
For me, using a out of the box talking house 4 in my house with the wire antenna on the indoor side of an exterior wall with the top few feet of it next to the ceiling and my ground conductivity of 2, I get about a quarter mile range to a car radio, as best as I can figure based on where I can drive in my neighborhood near my house. If I can pleasantly listen to the signal then I am in range. A usable signal goes out farther but it is not enjoyable to listen to the static; it is not a hard cut off.
OK I'll try and explain a little further. At the last meeting Station8 did give the exact conditions as to the range and the carrier quality and Audio quality such as 5 by 5, 3 by 4, ect. While he drove and listened to the station on a Radio in his truck he heard his station solid to 4 miles and then it faded to the fringe at 4.6 miles. Some directions were a little stronger than others. He has been giving me some updates as he tweaks and tries to get mass material to construct some identical antennas for the beta testers at the ALPB who was chosen and wanted to see what the range was in their area. These testers will have variable conditions with a few testers having the same conditions. I'm one of them. I live in a suburban area where as its not in the metro area. Being in town we do have a few obstructions. However it is not as bad as towns with skyscrapers. The land is repetitively flat. However there is a noise floor on AM here when the summertime hits and there is hydro noise. We'll see if I get the same range or better with a nice quality audio. Since I run the Advanced Talking House 5.0 AM Transmitter I should get some nice range. If so I'll really concentrate on AM as my main transmitter. Attending the ALPB will allow you to get the data from the horses mouth. You can ask questions and take notes. Until the antenna is perfected and on the assembly line, some data will not be disclosed as to how the antenna is put together to avoid someone stealing his hard work. I can tell you this though, no two part 15 transmitters get the same range from this antenna. But and here is the kicker the Talking House and iAM transmitters have been getting the best Range from his new antenna. This is great news for those who don't have the mega bucks to pour into a part 15 AM Transmitter. Another thing I will tell you is that there was no expensive processing going on in his tests. In fact the boom box was simply plugged into the Talking House, Procaster, Sean, Rangemaster transmitters and nothing else. Right now he is working on a way to use the wire side of the Talking House and have a small lead connected to the antenna. This will allow folks like myself to have a stealth antenna that the Land lord won't know about in order to complain about. You use an L bracket and allow the window screen and frame to pinch the bracket and hold the antenna. Maybe have a small bolt or screw to hold it in place. Nothing that would draw attention. The other version is of course the Antenna/ATU connected to the 75 ohm input if the transmitter. Being a part of the ALPB does allow one to get data on these things and of course it is FREE to join. Hope this helps.