Loading antenna

[WL74]

When I got my hand held radio out of the box I testing the signal and it was 1db on NOAA channel 1 ... when I tested it using about a 10ft copper load I got a 2-4db gain! Not bad for a little bit of copper. I did have to move the load up and down to find the sweet spot and I got it

[WL74]

Oh I forgot to mention that the load itself was 39" and cut from a 10ft reel lol. Yeah I was just thinking about that and I was like um no thats not what I was trying to say

[drdx]

A proper length antenna for the weather band is 17 inches, but be sure not to try to transmit cb on it. Most of the time, the cb antenna will pick up the weather band fine as it is. The formula for a quarter wave length antenna is 234 divided by the freq. in mhz for the length in feet. SO.......234 divided by 162.4 (a common weather frequency) is about 1.44 feet, or 17 inches.

-drdx

[Red Warrior]

You are not really seeing "gain". If you put a variable resistor between the output of the radio and the antenna and dial it up and down, you will see a change in signal strength but this is not gain.

A fellow Air Force veteran (retired 1983).

[WL74]

You are not really seeing "gain". If you put a variable resistor between the output of the radio and the antenna and dial it up and down, you will see a change in signal strength but this is not gain.

A fellow Air Force veteran (retired 1983).

Nice to meet a brother in arms - thank you for your service! Yes thats what I meant lol so gain would be transmit? I am just used to that terminology from being a soundman in a band and calling any increase in decibel - gain Well I am learning as I go hehe.

[WL74]

Well I have observed some interesting results from my tests:

1. My mobile antenna is already center loaded (coil in metal tube) therefore no additional loads resulted a signal improvement.
2. A 7 foot copper coil is actually more effective than the tube extension.
3. My hand held antenna's performance is very poor (lack of grounding) but is significantly enhanced with a simple copper coil.
4. Grounding is VERY important! I hooked my little Cobra 38 to my 30+ft radio antenna and I got a good boost

Well I have learned a lot from my first series of tests! Next up will be mounting my mobile antenna to the Mustang My mobile antenna is a magnet mount BTW. I will see what I can get with the SWR meter once it comes in and hopefully I can get a satisfactory signal and SWR reading

['Doc]

WL74,
It's probably just a difference in how you are describing things, but I'm having a lot of trouble understanding what you are saying about your set up. For instance.
Your antenna has a coil in a metal tube? Which antenna is that? I don't think I've ever seen a loading coil inside a metal tube, that would tend to negate a lot of why a coil is used to start with. Or do you mean that the coil is wound in a tubular shape?
"A 7 foot copper coil is actually more effective than the tube extension.", I would expect so. A coil 7 feet long will produce a lot more inductance than an extension no matter the diameter of that 7 foot coil, unless that extension is -considerably- longer than 7 feet. An extension/straight conductor also has inductance, but is typically -very- long in order to match the inductance of a coiled conductor.
I would certainly expect the antenna on a typical hand held radio on 27 Mhz to be less efficient than a longer antenna. Adding a coil to that hand held short antenna in effect makes it longer. Actually has very little to do with 'grounding', which is the "other half" of the antenna, which is usually the chassis of the radio, which hasn't changed from the way you describe it.
"Grounding is VERY important! I hooked my little Cobra 38 to my 30+ft radio antenna and I got a good boost.", couple of things that. Depending on exactly what you mean by 'grounding', it can certainly be important. In one meaning of that 'grounding' you're talking about the "other half" of the antenna. If that 'grounding' supplies the required characteristics to make the whole antenna (vertical portion and the ground/groundplane/counterpoise or whatever you want to call the 'other half') at least close to resonant, then it will certainly produce a better signal. The receiving side side of things isn't nearly so 'picky'. Receivers tend to hear more signal with longer antennas. I would expect you to hear more with a 30 foot antenna rather than the one that came on any typical hand held radio. Transmitter are a completely different 'animal' than receivers. Transmitters tend to be very 'picky' about the antenna connected to them. Transmitters want to see a particular impedance, they don't produce as much power the further that impedance is from what it wants to see (in either direction, hi/low impedance, which is typically measured by SWR). An antenna being resonant, defined as not having any reactances present, also makes a difference.
So adding to an antenna's length by either adding longer conductors, or by using a loading coil, will usually result in hearing more. I certainly agree with you there. But I'm confused by how you are stating what you are doing, and because of that confusion, hesitate in saying that your conclusions are in fact, true. (Did that make sense?)
- 'Doc

[WL74]

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There's the pictures of the antenna and the tube that contains the factory load coil. This was a cheap magnet mount antenna (dont remember the brand) But it works well stock. So the mobile antenna is good out of the box but the handheld antenna is the one that needed the copper load. So the handheld chassis is grounded because of the batteries having the complete circuit?

Well I fully charged the radio and found out what the descrpencies were last night ... It was the POS walmart antenna. SWR: 2.5 on both 26.965 and 27.405.
Should've went with a big good mag mount from Cobra from the get go instead of this $15 POS LOL. Oh well.

[WL74]

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Heres the load I put on there. Now will that harm my transmissions? I know it helps the incoming signal but I want to be sure it wont heat up my radio.

['Doc]

About the loading coil in a metal tube. I think I would want to have the thing 'in hand' before commenting on it. A metal enclosed loading coil on an antenna is NOT very common.

As far as the wire on the rubber-duck antenna, it may be shaped as a coil, but what it's doing is changing the permeability of that rubber-duck's coil. Sort of like that metal slug that moves up/down inside some coils. If it improves what you hear, then there's a chance of it improving your signal, but only a chance. That change in the rubber-duck's impedance will affect a transmitter much more than a receiver. How can you tell if it'll help? Simplest way is to try it and see. Sort of doubt if it'll harm the radio, but it will certainly change it's behavior. Good/bad change? No idea.
- 'Doc

[WL74]

Well I know that it helped the weather band but it did not help the CB band. So the copper coil works for increasing the NOAA signal but blocked out the CB band that I heard on skip. Weird.... So the copper coil may reduce the ohm load of the rubber duck therefore may/may not improve transmission?

['Doc]

"So the copper coil may reduce the ohm load of the rubber duck therefore may/may not improve transmission?"
Well, sort of. What it's doing is changing the reactance of the antenna, which can change the 'ohm load', or impedance. This is dealing with alternating current, RF, so there are different characteristics involved with it. Big differences between AC and DC, and RF is AC. As if things weren't complicated enough ?
- 'Doc

['Doc]

Oops!
Can it change how the thing transmits? Yes. Will it 'improve' it in some way? I doubt it. But then, there's not much you can do to a 'rubber duck' antenna to make it much worse! ... unfortunately.
- 'Doc

[Circuit Breaker]

I'm kind of lost as to what he's trying to do. The antennas he's talking about are designed the way they are for a reason. There will be very little he can do to increase their performance without actually changing the antenna. He says the Wal-Mart antenna is a POS...well, yes and no. He had a bad match because he didn't have the antenna sitting on the car so as to provide a ground plane for it. If he were to have done that, the match would probably be fine. The coil, more than likely, is not in a metal tube....it is plastic. Like you said, Doc...having it in a metal tube would make no sense. The RF would just go up the metal tube and not even see the coil...which is needed for loading so the antenna is electrically 1/4 wave length.

['Doc]

The only way I can think of, or at least the simplest way of increasing what a receiver with a rubber duck antenna hears things is to inductively couple that 'duck' antenna to a longer one. (wrap that 'duck' with the wire, in the same direction the 'duck' is wound. The more wire wrapped on the 'duck', the greater the coupling, and the greater the chances of hearing stuff. The longer and higher (especially at VHF) that wire antenna is the better. That's not that easy to do in a vehicle, but 'fixed', it isn't -that- difficult, sort of.
Transmitting? I very much doubt if it would help at all. The only alternative in improving a rubber duck antenna is replacing it! Or stand on top of a very tall building? That gets sort of limiting though.
- 'Doc

[WL74]

Well thanks for your input! I tossed that old mobile antenna out a few days ago but it looked like it just wasnt built well and would've probably just fallen off of my vehicle.