Here's the problem, gang. I know some of you have read this ad before and knew enough to simply poopoo it off right away.
The trouble is we're getting questions from people that *believe* what is advertised.
The item of which I speak is the amasing "Ultimate FM" antenna foisted upon the uneducated by Radio Brandy.
http://www.radiobrandy.com/FMAntenna.html
This antenna is SO amazing that it DEFIES THE LAWS OF PHYSICS! Anyone with even the most minimal knowledge of radio signals immediately knows that this advertisement is complete and utter bold face lying. First of all most of their testimonials are clearly from people who can't possibly be legal. Unless of course they're actually running a 7 watt transmitter that is running so poorly, and with the system so ineffeciently designed that they are still managing only the legal 250uv/m @ 3 meters.
What needs to be simply and clearly stated, for all those who inquire about the amazing comverage they expect to get using this "Ultimate FM Antenna" is that if they are Part 15 legal, meaning no more than 250uv/m @ 3 meters their signal is not going to be listened to at a mile away. Or a half mile away. It may indeed be possible to be a mile away with an incredibly sensitive field strength meter, with a good, external, directional antenna, and be able to find the signal and take a reading and come up with something ridiculous like 0.0000000675 uv/m that has been mentioned in other posts, but really that number is so far down into atmospheric noise that it doesn't even matter. That's so far down below anything receiveable by even the best radio built that it just doesn't matter. The fact that a super weak signal may be identified doesn't mean it's "coerage area" or that it can be heard by a radio.
The ad for this antenna is clearly violating every possible rule for advertising. It's like saying "Your 1986 Buick that gets 16 miles per gallon will get 1600 miles per gallon when you put on these Ultimate Mileage Tires". It's just not posible, folks. It's not a matter of if engineers agree, it's a matter of being able to change the laws of physics. And as Scotty once said "Aww Jim, I cannot change the laws of physics".
So many who get interested about Part 15 do a little web searching and come across the Radio Brandy web site and get sucked in by this and it bugs me.
Bottom line, ladies and gentlemen, is if you are at 250uv/m at 3 meters no change in antenna is going to get you more coverage. If you put up some sort of gain antenna and are 250uv/m at 3 meters in the sweet spot, the rate that signal strength drops off at greater distances remains the same. If you invent a magical antenna that gives you 250uv/m at 3 meters, and also at 4 meters, it would NOT BE LEGAL.
The Ultimate FM Antenna advertisement on that web page is chock full of out and out lies, wives tales and fantasy. Apparently they spent an amazing 17 years desiging a copper dipole. I built my first amazing copper dipole when I was 11 years old. That was in 1969. I would have gladly shared my notes with them and saved the all that time figuring it out.
Tim in Bovey
AKA "Mythbuster"
i have often thought a Circularly Polarized antenna for Part 15 FM might work good. you can double your power and still be legal. it puts 250uV/m @3m in the horizontal and in the vertical planes.
LOL, that's good. Just in case you have a hovering Gyrocopter a couple hundred feet above your station! Hahah.
Tim in Bovey
Now, in addition to our popular Placebo Pills in a real brown bottle, we have Improved Snake Oil from rare exotic snakes!
From the mystery of the ancient past, Snake Oil has long been known to increase the body's Energy Field and Amplify Healing!
This is not spam. I am talking Health and Recovery.
Snake Oil is nature's Ultimate Cure.
In the ad the statement is made that this antenna design " CONTINUES TO DEFY BROADCAST
ENGINEER'S [sic] UNDERSTANDING OF RF DESIGN;
THEY SAY: "THERE IS NO WAY IT CAN WORK AS DESIGNED "".
It would therefore be a very good thing if the designers would explain how it works so the doubting broadcast engineers and hobbyists can understand why it works as designed. Please educate us.
It is noted that the quotes from users cite power levels which will far exceed the FCC unlicensed field strength limit even if used with the most basic antenna, and maybe it is intended for use outside the USA. There was no mention that I saw of legal U. S. operation in the linked ad. Perhaps they would also like to comment on this.
Neil
i have one similar to the ultimate antenna made by a chinese company. it is simply a piece of 50 ohm coax with a connector directly attached to the dipole elements without a balun. it eliminates the balun but i haven't tested this beyond 1mW TPO of power there likely would be noticable coax radiation because of the lack of a balun at higher power levels. i can't see that it works any better than a normal dipole with a balun in line.
after system losses with 1mW TPO the range on the same frequency and general location as my certified unit yeilds shorter range than my certified unit.
the reason i suggest CP antenna for part 15 use is i would think you would get some kind of range regardless of the orientation of the receiving radios antenna.
if your primary target is moving vehicles through a small network of part 15 fm's then yes straight vertical is best.
i haven't scored a CP yet to experiment with and prove my theory. i will at some point in time.
The only way to double your power with a CP antenna is to have a 4 bay. A CP antenna by itself has negative gain because the circular polarity cancels. So you would need 2 for unity gain. There are better ways to get gain. The advantage of CP is less multipath effects. <Rich insert comments here>
well i was thinking 250uV in horizontal plane, 250uV in vertical plane not thinking so much for actual gain.
There is no need to use a unity gain transmit antenna for Part 15 FM. In fact using an antenna with 10 or 20 dB loss would be useful toward producing an FCC-compliant field with many of the uncertified transmitters used for unlicensed FM.
A perfect c-pol transmit antenna consisting of a single element or bay has less than 1/2 the r.m.s. gain of a linear, center-fed 1/2-wave dipole antenna -- typically about 46% of that gain, per polarization.
So the antenna input power needed to produce a 250 µV/m r.m.s field three meters in the direction of maximum gain and in any polarization when using a perfect c-pol element is 1/0.46 = 2.17X (approx) the power needed by a linear, center-fed, 1/2-wave dipole.
That would amount to about 2.17 x 11.43 nW = 24.8 nW (0.000 000 0248 watts), approx, which would not strain most of the uncertified, commercial "Part 15 FM" transmitters available.
The bigger strain would be in accurately adjusting those transmitters to produce that little amount of power.
P.S.: C-pol transmit antennas are far from perfect, so even though their r.m.s. fields may meet FCC §15.239, maximum fields might be exceeded in some directions and some polarization planes.
No, so you don't know what the zip you are talking about. The Ultimate FM Antenna page, states the input power to the antenna by various users around the world. I have an FCC agent, who heard it 21 miles away; with just 500mw feeding it at 15ft above ground; even he was impressed with the coverage. He also heard our 1/4 wave ground plane, with same input power at 30FT above ground; and left very impressed with Ultimate! Oh he also asked that we not use them again! We have many users who have gotten excellent results from the antenna, when compared to the Comet or 1/4 wave GP. Tim you are in clueless MN, in the land of make believe. The antenna never states it's for Part 15 use, in fact one person asking questions; has repeatedly been told it is not for part 15 use at 30mw. Unfortunately, different FCC agents will give a dozen different answers to the same question. In Boston, an agent passed a station using a Ramsey FM35, feeding a Dominator antenna at 15ft above ground. One in Florida, passed a Ramsey FM100 feeding a Comet. The fact is the antenna is legal, it depends what you are feeding into it; and if you have a permit to do so. In New Zeland, our antenna is legal and used by dozens of FM stations with 500mw input power. As the person was told by me, it is all about field strength; not power.
Thanks, Radiobrandy, for the clarification.
Neil
Well, nobody said the antenna is illegal to use. It's not uncommon at VHF frequencies for 1/2 watt to cover 15 miles with a decent antenna. I guess all of the "micro broadcaster" testimonials featured from operators in the USA must have licensed stations.
But even so, anything you do which increases your range increases your ERP. The FCC license process stipulates the allowed ERP when they issue your license. So, I suppose the "micro broadcasters" would have to reduce power to maintain the correct ERP.
As for Part 15 FM broadcasters field strength is field strength no matter how little it takes to get it. Just don't exceed the limit and you're OK.
Yes, the FCC agent may be impressed but as you said he told you don't do that.
Until I see an independent comparison of antennas, I view any claims as dubious. Particularly from the supplier.
And sometimes it's what you DON'T say that is more important. I highly doubt that ANY external antenna would be found in a legal installation, at least in the U.S. Why bother when you're dealing with nanowatts and puny field strength? What I see is nudge nudge wink wink promotion to those who either don't know the rules, or don't care. Change the wording to clearly state that the testimonials are not legal in the U.S. and I'll gladly change my tune.
Canada only allows 4 times the field strength of the U.S. We still deal in nanowatts, just a few more of them. There's just as much chance that this antenna would be used legally in Canada as in the U.S. - which is not much.
And as an administrator here, I have to issue a warning that personal attacks will not be tolerated.
RADIOBRANDY posted: ... The Ultimate FM Antenna page, states the input power to the antenna by various users around the world. I have an FCC agent, who heard it 21 miles away; with just 500mw feeding it at 15ft above ground; even he was impressed with the coverage. ...
Below is a link showing the loss for a 21-mile (33.8 km) path over the surface of smooth earth for a transmit antenna elevated 15 meters above the earth to a receive antenna elevated 2 meters above the earth.
Note that more than 90% of that path length is obstructed by earth curvature, which means that the field intensity at the receive antenna is more than 60 dB below the value it would have for a free space (unobstructed) path. See the numbers enclosed in the red rectangle in this link.
Even if the ERP from the transmit antenna in this system that was directed along the surface of smooth earth was 2 watts, the field at the receive antenna at the end of that path would be less than 0.3 µV/m -- which would be unlikely to impress an FCC agent, or provide useful service to users of typical FM receivers.
