- January 18, 2018 at 7:10 pm #11546
Below is a NEC4.2 analysis of an elevated transmit system for Part 15 AM that needs/uses no radiating conductors exceeding the total 3-m length permitted by FCC §15.219(b).
Possible issues are:
1. How the system can be powered and programmed without radiation from those necessary conductors.
2. The internal loading coil such as included within some commercial transmitters may not have enough inductance range to resonate this antenna system.
3. The physical challenge of optimizing the system when installed on a 10m supporting structure.
4. Possible r-f bandwidth and tuning stability issues due to the high reactance of the antenna system, before resonance.
Anyway, here it is …
- January 18, 2018 at 9:34 pm #56427
Not that I’m knowledgable about such matters, but isn’t the elevated xmtr finding ground via the power and/or audio runs a factor to consider?
Edit: Sorry, I see you account for the power run (battery I presume), so I guess maybe the audio would be fed by an mp3 player or something.
I suspect maybe this might be refering to how the elevated part15AM transmitters at state parks or wildlife refuges and such might operate.. If so, that’s not the case, as the case studies clearly say that a good ground is very important in the installs.
- January 18, 2018 at 10:37 pm #56429
My post was/is not intended to describe the installation of a Part 15 AM system by anyone past or present, but to show what might be possible for an elevated installation meeting the description shown for it there (especially, one having no ground wire or ground connection).
- January 19, 2018 at 12:01 am #56430
I was just making assumptions (occassionally a bad habit of mine).
Anyway, I really don’t comprehend how to read that chart to determine what a ‘rough guess’ estimated range capabilty might be.
- January 19, 2018 at 12:47 am #56431
The last bullet in the list shows a groundwave field of about 0.13 mV/m at a radius of 1 km from that system. That signal and even a bit less would produce fairly quiet program audio output from a good AM receiver in an area of low radio noise and other interference.
- January 19, 2018 at 2:57 pm #56432
1 km is a little more than a 1/2 mile radius.. That’s more than I would expect for a 15.219 install with absolutely no connection to ground. It’s also a bit more than I am acheiving with my present elevated ungrounded Rangemaster with the audio and power cables running to it – but I’m only at about 20 foot.
–Or maybe it isn’t, I’m not sure how to calculate distance on Googlemaps, but this is a rough estimation of my coverage, although it is not receptive in all ares of the shown radius.. the reception is rather sporadic in the shown area:
- January 19, 2018 at 3:57 pm #56433
Wow, End80, your island is really crammed with streets and buildings!
Forgive me if you’ve previously said, but maybe carrier current would be the bootstraps you are looking for.
- January 19, 2018 at 4:54 pm #56434
RichP: It looks like WSPO, 1390 khz in Charleston, SC should put a daytime, groundwave signal of ~ 0.15 to 0.2 mV/m in Tybee Island, GA. You might want to compare their signal-noise ratio etc to yours, for a rough idea of your signal strength around your transmit site.
Of course overhead wires, receive antenna orientation, local r-f noise, and interfering stations will or might affect receiving those two stations differently — but it could be an interesting exercise.
- January 19, 2018 at 7:42 pm #56435
Carl, although I’ve continplated carrier current in the past, there’s transformers on about every block so I doubt it would be much of a solution, besides it’s way more complicated proccess which I have no familarity about.
It’s ridicuolous that I haven’t accomplished anything with genuinely getting my station off the ground in a worthy manner as planned.. but you know; every summer time I usually work 10-12 hours 7 days, sometimes even more, and that makes it difficult to find time to impliment a working system of multiple transmitters, securing locations, putting together an array of local programing for tourist and locals to tune into, and so on and so forth… Come winter there’s plenty of time, but no more income coming in, what cash I have on hand always is needed to pay bills and get by through the winter! – It’s like a catch 22.. ahh… excuses excuses.. Someday will come one day.. when I quit making excuses.
RFry, Not sure about 1390, but I usally have my home radio on 1700 (my broadcast), but I often listen to 1290 which comes in good in the day, but is terrible later ( I like to listen to George Noory’s C2C at night, but it’s reception at night sucks, so I just listen to it via internet on the Ruko.
Within a few blocks my 1700 signal is strong and clean, but like I said it’s not consistent at all in the radius. A lot of spots get no reception, and then a 1/4 block further it will come in again only to dissapear again around the corner.. there’s no ryme or reason to it.
The ground conductivity here is 8, but I have acheived much better results at installs 60 miles further inland where the ground conductivity is only 4. There’s something about this island which just doesn’t like to play with my part15AM signals.
But the objective is still workable, it’s just going to take multiple xmtrs and locations.
- January 20, 2018 at 6:37 am #56436
With all that all around you even a few blocks around you would get hundreds of possible listeners.
- January 20, 2018 at 4:03 pm #56437
Yeah.. I sometimes wonder about that. You know, growing up, it seems like there was always a radio on the kitchen countertop, and a stereo system was always prevelent in the living area of everybodys home. Tuner, amp, turntable and tape deck, etc.
But it seems nowdays in the home I’m more inclined to see some kind of computer-based media system with surround-sound components.. There never seems to be a regular ole radio in house anymore, except maybe a clock radio in the bedroom. But maybe that’s just around my area. Then there’s also the matter of the home dwellers – presuming they even have a radio at home -needing to utilize some kind of external AM antenna booster, maybe even to the outside to enable reception of weak part 15 signals unless they are within the same block or so..
I don’t know, but that’s how it seems. I guess that’s part of the reason why I’m more inclined to be concerned mostly with the automobile reception to the general area, as all they have to do is tune the dial – Also because since this is a tourist town the greatest majority of listeners would be those tourist. Not that intentions aren’t catering specifically to the locals as well.
I just don’t know – but I think the nearby apartment dwellers, the local businesses surrounding, and those cruising the strand are likely to be the most predominate potential listeners. I have a hard time beleiving many will be able to adequately be able to recieve the signal inside their houses unless very close by.. I know a handheld radio a block away inside a house has a very difficult time picking it up, and like I said, I just never really see home radios so much anymore in the home..
Of course it my perception could be way off… Did I say I just don’t know?.. Well, I don’t!
- January 20, 2018 at 4:08 pm #56438
Sorry R Fry, I’ve apparently took this thread way of course from your original topic of ungrounded install capability.
- January 20, 2018 at 4:35 pm #56439
…often evolve. OK with me, as long as they don’t evolve into nonsense or personal attacks. YMMV.
- January 20, 2018 at 5:19 pm #56440
I had to google YMMV, in this case I guess you mean YMMVWP15 (Your Mileage May Vary With Part 15)
Actually, YMMV would be an appropriate call sign for part 15!
- January 20, 2018 at 7:09 pm #56441
It would be interesting to setup the mast mount system as described along with a ground mount system over a counterpoise to see how they compare in a real world test.
Would height win out over a good ground system…
- January 20, 2018 at 8:33 pm #56442
I could compare them using about 15 minutes of NEC modeling. I’m quite sure as to which configuration would win, already.
Maybe a volunteer will appear to do the real world tests described (sorry, not me).
- January 20, 2018 at 10:20 pm #56444
In HB’s transmitter challenge the Rangemaster broadcasting on 1640 acheived just a hair under a full mile with an umodulated signal, ground mounted and using a single ground rod with no radials in an area of only .5 ground conductivity.
I tell you what, I must be doing something wrong – even though I’m presently elevated and ungrounded, lately I’ve been wondering if my now 15 year old 102″ fiberglass whip has lost it’s gusto or something.
However, the area which Bills challenge took place appears to have been a wide open feild area without buildings or other obstructions, or power lines and so forth, which is quite different than being surrounded by all that stuff.
- January 20, 2018 at 11:09 pm #56446
…Point being that a ground mounted legal install should substantially outdo an elevated legal install.
- January 20, 2018 at 9:54 pm #56443
but it sure gets the brain going.
Some of us have wondered about
magnetic transmit loops. I don’t
know about the length measurement
with regard to Part 15.219…
- January 21, 2018 at 1:00 pm #56448
From Reply #17: Some of us have wondered about magnetic transmit loops. I don’t know about the length measurement with regard to Part 15.219…
Brooce – Probably a “legal” case could be made for using a circular loop antenna for transmitting under Part 15 AM, as long as the circumference of that circle plus the length of any other radiating wires used with it don’t exceed the 3m limit of §15.219(b).
But unfortunately, a small (in terms of wavelength) loop antenna is not a very efficient radiator — quite a bit _worse_ than a base-fed, linear conductor such as a ~ 3m whip.
Here is a link to some resource material about this:
- January 21, 2018 at 7:10 pm #56449
Interesting information – – I do
I have been working with receiving loops
for the AM BCB and shortwave for a long
time. I’d like to try transmitting Part 15 AM with one some day. I’d like to try
all of the things you guys are talking about actually.
- July 6, 2018 at 6:06 am #104820
Tim in Bovey has an elevated Procaster mounted outside his house. Uses no ground and covers his small town as well as the town next door quite nicely.
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