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Here is an interesting advancement in AM broadcasting, an Underground Virtual antenna.
http://www.am-va.com/Or go to their article in RadioWorld.com on page 70 & 71
Here is an interesting advancement in AM broadcasting, an Underground Virtual antenna.
http://www.am-va.com/Or go to their article in RadioWorld.com on page 70 & 71
http://www.nxtbook.com/nxtbooks/newbay/rw_20080326/
Total posts : 45366Reminds me of a presentation I attended back in the mid 70’s at the Baltimore Grotto (a caving club affiliate of the National Speleological Society). Some ham/cavers built a few portable AM transmitters that broadcast at the low end of the AM band. They got an experimenter’s license from the FCC and did tests to determine how best to use these radios for communication between ground-level and inside a cave. The low frequencies worked just fine. The real drawback was having to string out a long piece of wire for the antenna.
I think they were going to do further trials with loop antennas. I don’t know what the results were, but I suspect a proper loop would be more convenient, although more problematic, due to the nulls.
BTW, the US Navy uses VLF for communicating with subs while under the water. They have huge antenna arrays for this. Of course, the drawback with VLF is the low data rate.
Total posts : 45366by MRAM 1500 kHz
Reminds me of an April Fools joke this site put on a couple years ago regarding obtaining a special class AM license. The part about the cattle particularly.
Total posts : 45366If you spell their names backwards you will find the anwer
Dr. J. Parcfolluf IV – Full of Crap
R. Langison – No signalApril fools on me.
Total posts : 45366It at first looked to me like another antenna scam (Like CFA and EH), but this one was not intended to be anything but a spoof.
I’ve been fooled by some April fools articles in the past. CQ printed an article by “Dr. Jerzy Ostermond-Tor” about a proposed telephone service that was supposed to simulate amateur radio. Subscribers to this service would be connected to other subscribers throughout the world at random. It sounded plausible enough until the realization suddenly came to me that Ostermond Tor means “Easter-month fool” in German. Then there was another article in CQ that continued to fool me even after I recognized that the author’s name “Dr. Shorza Kitchagoome” as being from the first line of Longfellow’s very bad poem, “Song of Hiawatha.” The title was “Zero-Bandwidth Communications.” The author claimed that it is possible to communicate with zero banwidth by slightly deflecting a small antenna producing a narrow beam. The deflection amplitude and rate would follow an audio modulating signal. Amplitude modulation would be produced by the rapidly-deflecting beam at a distant receiver. The signal bandwidth would be zero because the antenna was only transmitting the carrier. Other than the practical problems with deflecting even a small antenna rapidly enough to get AM, the idea, at first, seemed plausible to me. The fallacy was that the usual audio sidebands would be created by Doppler shift, and the transmission would not be zero-bandwidth at all.
However, Dr. Kitchagoome’s modulation method could, in principle, be applied to getting high efficiency from a Part 15 AM transmitter. As has been discussed in this Forum, with high enough Q, an electrically short antenna can be 100% efficient, but very high Q would prevent modulation sidebands from being transmitted. If you have a short horizontal dipole with an end pointed at a receiver, you could rapidly deflect the dipole to get an AM signal at the receiver. AM would be present at the receiver, while the antenna would only transmit a carrier.
By the way, it is entirely possible to transmit a strong, vertically polarized, signal without any protruding structure above the level of the earth. I mentioned such an antenna in 1989 in the ARRL Antenna Compenium , Vol. 2. My article was about installing an antenna in a location where it had to be completely concealed. I gave construction details about an invisble antenna installed in a window, but I also mentioned a similar antenna, described in Kraus, where the structure is underground. A narrow trench, 1/2 wavelength long and 1/4 wave in depth, is dug in the earth. The walls of the trench, and the area outside the opening of the trench, are covered with solid metal or screen. Power from a transmission line is applied across the opening at the top of the trench in the narrow direction. Of course, some low-loss dielectric cover would have to be used to keep the rainwater out of the trench. The trench has to be rather large at medium frequencies, but such an antenna is possible to construct.
I promise that I’m not joking.
Total posts : 45366Nice post Ermi. You have probably heard of the directional discontinuity ring radiator (DDRR) which goes by other names and was developed for MW use on Navy craft. Sounds close to Krauss’ antenna you described. MY best understanding of this is it is a bent transmission line and somehow radiates. Never built one but I read the description with interest.
Years back I was very active in amateur radio based community emergency communications, one aspect of which was a weather net during tornado watches/warnings. At the time it occurred to me that with the lightning associated with storms it would not be a good idea to have an antenna 35 feet in the air connected to my radio and, through the microphone cable, to me. I built a simple 2 meter 1/4 wave ground plane antenna that I hung from my basement ceiling and could work all the area repeaters well. As I bragged on air about this it became known as the “subterrainian ground plane” and I was urged to publish in the local ARPSC rag the details. There was no new science here, just a new way to use the old stuff.
I also played around with a passive repeater where I connected my sub-t antenna to my roof antenna and the induced field from my handheld was enough to work many repeaters.
So, not everything that sounds as if it came from a sci-fi movie is fiction, but some is I suppose.
Neil
Total posts : 45366The antenna described in Kraus’s textbook is a half-wave slot antenna facing upward. The antenna is fed by a transmission line connected across the slot, but the transmission line only supplies power from a transmitter, and is not part of the antenna. The trench under the slot, which is a quarter wave deep, forms a resonant cavity. A slot antenna is a magnetic dipole, and, because of that, a slot oriented in the horizontal direction provides vertically polarized radiation. The radiation pattern is not omnidirectional, and has the shape one would expect for a horizontal dipole. This antenna truly has no structure above the surface of the earth.
The DDRR, which has a short vertical element and one or two horizontal loops, has all of its structure above the surface of the earth, and so is not a subterrainian radiator.
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