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.