Quote=mram1500
Reading the posted violations on the FCC site, they always nail someone for exceeding field strength limits which are 15.209. I've never seen one say that a ground wire was to long.
But one strong possibility as to WHY your signal exceeded 15.209 is a radiator length that exceeded 15.219(b). Why not install a compliant radiator, and take advantage of the added field it will produce above the limit in 15.209?
By the way, does a properly designed ground counterpoise not radiate for the same reason that a top hat doesn't radiate?
Yes. Currents flow in those elements but the net radiation from them is zero because of the mechanical arrangement and the direction of current flow in them.
And if a top hat doesn't radiate, why does the top hat radius figure into the 3 meter rule? I read that somewhere.
I haven't read that, and physics doesn't show that it should.
Quote=kk7cw
For a little something to tweek your Part 15 thinking, consider the Isotron model 200-B antenna for Part 15 stations by The Bilal Company.
This antenna emulates a resonating tank circuit with reasonable efficiency. And NO ground to boot. No elevated ground, no ground radials, no downlead, no counterpoise and thousands of these are in use in all kinds of conditions and service all over the world. And its only 8 1/2 feet long. HMMMMMMM.
I believe that the website info for this antenna recommends a ground lead, does it not? It's been a while since I read it, so I'll look again.
Of course, a ground lead becomes part of the radiating structure of that antenna, just as with the more conventional designs used for Part 15 AM.
(The text below was added after posting the text above)
After visiting the Isotron website, this design for AM appears to be essentially a base-loaded, linear radiator having additional structures on each end, which can add a small amount to the radiation resistance, and reduce its capacitive reactance. The lower reactance could mean that the resistance of the loading coil could be a bit lower.
But this configuration has no effective r-f ground plane to work against unless that is provided by a conductor leading to one. The website page for the AM version recommends installing it on a "metal mast," which of course could provide the path to an r-f ground in/at the earth, as well as add to the effective radiating length of the Isotron antenna system.
The site also says it should be mounted "as high as possible" for best performance. That is a strong indicator that the better performance comes not from radiation off the Isotron alone, but also from the metal mast that is supporting the Isotron above the earth.
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by MRAM 1500 kHz
ISS is a company that supplies TIS and HAR station systems which operate in the AM band. They have a short article which shows how they recommend installing a groundplane radial system for there antenna. The link is:
http://www.theradiosource.com/articles-techtalk-powerplane.htm
For the upper end of the AM band they suggest 62 "loops" of copper wire each 10' long, equally spaced around the base of the antenna and all connected to a grounding ring at the base. For the lower end of the band they have you cut the loops to create 62 radials 20' long.
I read the article with some interest. I have investigated this site before. TIS and HAR services are licensed. However ISS does offer a Part 15 unlicensed system. And they mention an option/accessory of a whip antenna and matchbox. Also offered are feedlines up to 400 feet in length. I was OK until I got to this part of the sales pitch. Now I have serious questions as to whether these folks would provide a "FCC proof" installation. For about $2000.00 you too could have an ISS system ready for live community radio broadcasts. Even though they offer some pretty slick looking equipment, I am still going with the Hamilton AM-1000.
And finally, the suggestion for a ground plane using their construction technique is pretty cool. As long as the transmitter and whip were mounted just above the ground plane (transmitter mounted just off the ground), it would be legal.
Marshall Johnson, Sr.
Rhema Radio - The Word In Worship
http://www.rhemaradio.org
by MRAM 1500 kHz
Glad you pointed out the Part 15 equipment. Their unit looks very similar to those I've seen on Ebay; Got out-bid...
I work for a City Government. We maintain/install traffic signals, telephone systems, radio systems and also support all departments with most any type of electronic equipment/cabling.
Our City is purchasing a 10 watt licensed system from ISS to use as a Community Alert system. It's scheduled to be installed this year along with a city-wide siren warning system. I'm very eager to see the radio system installation particularly that ground plane system.
I'll try to put together an article about the install, no time-line on the install yet.
I keep losing this graphic and finding it again 🙂 Enjoy