I have to admit, I've thought "rubber ducky" is a dumb kind of name for a stubby flexible antenna, and I think it belongs back on Sesame Street, but oh well, it's commonly known as rubber ducky. At least it brings in a little laughter to dry technical discussions, along with "wall wart" which I never use in my writing. Oh wait, I just did...
Jim Bohannon just had on a guy who wrote a book about Jim Henson, so I just heard Rubber Ducky, the song 3 days ago.
I had a rubber ducky antenna that was "supposed to be tuned for FM" but on an MFJ meter it showed that it was more like tuned for 142 Mhz (Ouch). This is why if you have the equipment or have friends who will test for you it is best to try and do so that way you'll be less likely to cause a malfunction of your signal that can produce unwanted interference to other Radio services.
Doing some research on the famous chip BH1404 and the newer BH1415F chip there seems to be some fixes in the newer chip that helps to combat this issue as well. I wonder if that EDM transmitter is using the newer BH1415F chip? And since the C. Crane is so clean I wonder which chip that one uses?
I still believe that range testing is valid. Not that it says much about individual transmitters, but it goes towards showing the types of ranges that people can expect/hope to achieve in the real world under differing conditions.
When people ask me what kind of range to expect with my transmitter, the answer is (for my current installation) anywhere between 0 to about 300 meters, typical 100-150 meters, depending on the radio, direction, weather, etc. But at least I have ball park figures, based on my specific testing. If someone lives a mile away, well, they're out of luck.
Car analogies are often used here. Think of it as a car in which your fuel guage is broken. I can still operate it, as I know that, based on various factors such as terrain, speed, etc., I'll get anywhere between 250-400 miles on a tank of gas. I'll know approximately, based on al of those, when to fill up - I don't really need that guage.
Similarly (although I admit the analogy is flawed), you don't need a FIM to know that a legal FM signal (at least in the U.S.) is not going to travel 1/2 mile. My estimates there would be anywhere between 0 to 200 meters at the very outside, typically less than 50 meters.
Any range testing with ANY transmitter (along with all the environmental factors) just goes towards helping to narrow down what kinds of ranges you might expect in similar installations.
Here is something I ponder on as well. It helps too to describe your install when you report range. What your dwelling is made of rather brick, aluminum, rather your in a trailer, apartment and rather there are nearby trees and surrounding buildings.
Playing with these transmitters (even CB and 49 Mhz Walkie-Talkies as a kid and FRS and GMRS Walkie-Talkies and even 900 Mhz Audio/Video senders) I found that many things factor.
Carl Blare mentioned one time that he was listening to his C. Crane transmitter on a radio across his bed. Suddenly he heard the Wuuuussssshhhh of what he describes as a multi path sound. Funny thing as he looked around his house even outside and there was nothing he could find around him that would cause this.
I have found though some may disagree that fog will increase range of FM. To say just how much it does is something I have not been able to say X distance but I’ve noticed this even when playing with FRS walkie-talkies in the 462 Mhz area. Remember they describe a 2 mile range with those. But I’ve found in Arkansas at Loins World Services For The Blind that height has a lot ot do with this. Case in point Adam and Chuck were staying a hotel that was a few stories high. I was on the second floor and my room was on the outside of the school building. While sitting in my dorm I was able to have a QSO with Adam and Chuck 2+ miles away. But when they were not in the high rise Hotel and I was on the 2nd floor using the SAME brand walkie-talkie Bell South in case you want to know I was lucky to talk 1 ¼ or 1 mile. The signal actually got choppy before a mile.
I did find that the Cobra’s and Midland Walkie-Talkie’s did better. Probably cuz they had better receivers although I had no way to tell if they were over the limit for unlicensed communications.
So this is the reason why I always ask that question rather AM, FM, 49 Mhz, 462 Mhz FRS/GMRS, MURS or whatever. I like playing around with this stuff and trying different things to improve range and reception including vertical vs horizontal polarization and even circular polarization does spark my curiosity as well.
I pulled this out of my bookmark archives. This shows that in some cases you can acheive 600-800 Ft with a legal part 15 fm transmitter at spot on 250 uVm @ 3 meters. This could help if you have an engineer friend with a FIM to adjust your tx for dead spot on legal power:
http://radiobrandy.com/FM-Coverage.html
I haven't tested any antennas, simply because transmitters I have tested have been tested with the supplied antennas. So I assume that what they supplied is what they intend you to use. Except for the recent EDM test everything I've tested was certified indicating it was certified for use with the supplied antenna, and of course, changing the antenna would void the certification.
That said, the rubber duck antennas I've had with Part 15 transmitters were nothing more than a piece of wire in a piece of plastic. I see no difference between that and a piece of wire without the plastic around it.
The others all had whip antennas and no instructions in reference to extending them the proper length for the frequency chosen. I believe in most cases they depend on the poorly matched antennas to drop the output to legal levels. I think they count on the supplied antenna to reduce range to legal levels. And I suspect the output of these is so low to start with that there's not enough output or reflected power, to create enough heat to cause damage.
Take for example the EDM. I was supplied with a 63" wire as a supplied antenna. But they'll sell you a 10" rubber duck for an extra charge. So -- 10" or 63 inches, both OK by them. The C. Crane was supplied with a 10" whip. The Whole House came with a plastic whip that was shorter than 10". The Broadcast Vision I tested has a 19" attached whip antenna. Clearly none of these is supplying a matched antenna.
I have never tried testing a whip antenna or short piece or wire on my MFJ to see if it would ressonate anywhere, or if an accurate measurement were even possible. A "real" rubber duck antenna, for example, has more than a wire in it. The one with the Whole House, for example was just a piece of wire. Famously advertised as a "helix" I belive. But still, just a piece of wire, connected only to the center pin of the antenna and transmitter jack. Know where a 10" piece of wire, or a 10" whip antenna resonates? No where. Perhaps when installed on a transitter and one side is connected to ground you can find a resonance point. But a REAL rubber duck antenna is not simply a short wire connected to a center pin. A real rubber duck antenna actually has a helically wound coil inside. of the Part 15 supplied rubber ducks I've seen they're either a short piece of wire, or in the case of the Whole House, where I've seen an ad about it's "helix antenna" it's the same thing, a piece of wire, except it's a flexible braided wire, not actually a helix. I put one of these on the MFJ where it stayed pinned at the right side off the scale of the meter. They are just disguised pieces of wire. Granted, a lot more handy than a bare hunk of wire, and easier to connect, but as far as antenna's go they're a piece of wire.
I've seen NO Part 15 FM transmitter than came with any sort of "real" antenna. After all, a whip antenna is also just a piece of wire electrically. I can promist you any one of these transmitters would be well over the legal limit if connected to a dipole, yagi, j-pole or any other antenna.
A certified transmitter must either come with a "permanently attached" antenna or with a "unique connector" to prevent the user from using any antenna that it was not certified with. So that's what I test them with.
TIB
Yeah, that chart is kind of legendary. Originally from the Ramsey Electronics web site (where their mission was selling transmitters). I've tested a quite a few Part 15 transmitters now, and I can promise you that nothing even near legal will go 1200 feet. I've done it, in real life, in an open field with no obstructions. Someone has done a critical review of that charg and explained it's flaws, but I don't remember who.
I do have a C. Crane sitting right here on my desk that I kept after I did that batch test of 10 of them a few months ago. I sold them all, saving one for me in case I needed it for reference. As you all probably know there's a power adjust trimmer pot inside these buggers. In my tests I was able to adjust it to WAY over legal (although they ALL tested right abound 100 uV/m - legal - in my tests). Anyway, I adjusted this one as close to 250 uV/m as I could possibly get it, out in my test field this past fall. This spring, when the weather is nice and my field isn't all snow, when I'm out there to test something else anyway, I'll set it up and see what the range is. I can walk far more than 1200 feet without getting out of the field. We'll see what the real world has to offer.
This chart also assumes a radio with good sensitivity.
And this is a theoretical chart that assumes you're in an open field. So, if you have your setup out in the yard, perhaps. And takes into account no enviromental factors. It's in no way a "real world" chart, unless you're trasmitting in a field, surrounded by listeners in the same open field. If you're in the house, and they're in their house, and you have typical real world "stuff" outside in the neighborhood, these numbers are quite impossible to achieve.
TIB
Hi Tim & everyone: I will tell you my experience on the antennas !
Don't assume the company tested there antennas !
You need to Test them & will find some of them DO NOT WORK IN THE FREQUENCY YOUR USING !
I do know this from fact I have tested some of these antennas on my mfj 259b
The ramsey 100b antenna is NOT made for 88 -108mhz at all !
The rubber duck antenna for the sainsonic 05b worked in the 141mhz !
The cze adjustable dipole antenna did better from tunning from 99-108mhz
But need a mfj 259b to make sure you have 50 ohm & swr are low other wise
Your going to have a missed tune antenna !
On the cze adjustable dipole ant from 88-99mhz I had to add a piece of foil in
3/8 inch dimension & 10 inch long to make the antenna to work properly on
The low frequency and you will also need a mfj 259b to tune it correctly
Or could run into problems with a missed match antenna !
Here are some example why you need to check your equipment out before use
Do to you could damage your finals and or equipment or both !
This is why you don't assume the company tested all there products
Do to they get some of there stuff from other company and you have no
Clue what are there procedures for passing the products !
I have worked in the electronic industries field for 14 years and I know some stuff
That You would not believe !
I hope this help you guys out !
Have a great day station 8
I know this is getting a little off topic but the antenna that came with the wholehouse 3 actually was not just a straight 8" length of wire as I removed the cover to actually see it.....it was a coil about 5" and straight for about 3" where it went into the narrower top..this is referred to as helix? So I assume that particular rubber duck antenna is tuned or at least has the 50 ohm impedence but is still not as efficient as a longer length of wire.
Mark
Timinbovey's report about tests using professional-level test equipment made using a 10" antenna on an EDM FM transmitter posted at http://www.ironrangecountry.com/edmreview.pdf states that its signal was "clean with no identifiable harmonics or spurious emissions."
His measurements do not support warnings posted in this Part15us thread stating that using a mismatched antenna "can produce unwanted interference to other Radio services."
... .it was a coil about 5" and straight for about 3" where it went into the narrower top..this is referred to as helix? So I assume that particular rubber duck antenna is tuned or at least has the 50 ohm impedence but is still not as efficient as a longer length of wire. ...
The radiation resistance of all electrically short monopoles including a "Rubber Ducky" depends on the linear aperture occupied by that antenna -- which essentially is independent of whether or not that antenna has a helical form along any part of that aperture.
The radiation resistance of an antenna is the only parameter of that antenna that can produce useful electromagnetic radiation into space.
Considered by itself, an antenna does not need to have an input impedance of 50 ohms in order to be a very efficient radiator, as long as whatever input impedance it has is impedance-matched to the source connected to its feedpoint.
I find this discussion fascinating! And a tiny antenna like the coil-loaded Ducky, incredible! A wavelength on FM is what...9 feet or so? To get a 4 or 5 inch stub to resonate so cleanly is like magic to me!
A wavelength on AM is like 900 feet! So naturally, a coil-loaded is preferred. Ground radials play a big role, and my Comet FM antenna (now retired) had four counterpoise radials at the bottom, so I guess it's important for FM too. But Part 15 needs minimal on FM.
The CCrane is so small, you can set it on a shelf and cover the whole house! The SSTRAN and SpitFire need the 10-foor antenna strung up. But I find those tiny Rubber Ducky antennas amazing...
Doug
Comments about "resonance" as it applies to radio antennas ...
A popular belief about antennas that are physically short in terms of an electrical wavelength is that they can be "lengthened" by use of a loading coil.
It is true that some value of the inductive reactance of a loading coil exactly can offset the capacitive reactance of a short antenna at a given radio frequency, which by definition means that antenna system is resonant at that frequency.
However the condition of being resonant, by itself, does not produce radiation of r-f energy into space. The only source of such radiation is by the radiation resistance (Rr) of the antenna. Radiation resistance is determined only by the physical dimensions of the antenna in wavelengths, whether or not that antenna system is resonant.
The shorter the antenna in terms of wavelength, the smaller its radiation resistance. A very short antenna could have an Rr of 0.1 ohm or less, and a high value of capacitive reactance (1000s of ohms).
That capacitive reactance can be offset by a loading coil. But the loading coil has r-f losses that can be 10s of ohms, which is in series with the r-f current flowing on the antenna.
As an example of the affect of this on the radiation efficiency of the antenna system, if Rr = 0.1 ohm and coil loss = 15 ohms, then (neglecting other losses) the radiation efficiency of that system is 0.1/15.1 = .007, which is 0.7%.
Less than 1% of the r-f power applied to that antenna system will be radiated into space. The rest is dissipated as heat in the resistance of the loading coil.
OTOH, a vertical antenna with a physical height equal to 1/4 wavelength can have a radiation resistance of about 35 ohms, and naturally resonant without needing a loading coil. In that case its radiation efficiency is 35/35 = 1, or 100%.
So while both of the antennas systems above are resonant, their performance is far from equal.
(Sorry this got "wordy," but it takes a certain amount of words to describe these concepts.)
I have found that many times a "rubber duck" will fall into range when a 1/4 wave piece of wire is attached to the analyzer.
Rich,
Regarding the loading coil loss, would it be any benefit winding the coil from say 6mm copper tube, to lower losses ?
Of course the physical size would be large, but would be self supporting, so no former would be required ?
I notice that quite a few broadcast stations use copper plumbing for inductors ?
Paul.