I am connecting a wire to the negative battery spring of a scosche fmt4 transmitter.
My question is what wire is best? copper? stranded? solid? guage?
Right now I have it set up with a short piece of 18 guage stranded copper wire from battery negative spring, on the other end is the male side of a bullet connector. Then I have the female end of the bullet connector to a piece of solid copper wire 14 guage I think (almost as thick as a wire coat hanger.
I chose the bullet connectors to allow me to remove the transmitter from the site without removing the rest of the antenna. I chose the solid copper because I wanted the antenna to support its own weight when mounted vertically, if that makes sense.
I'm not sure this is the best setup for this transmitter so I humbly ask your advice.
Thanks
18 gauge stranded will be perfect. In fact, stranded radiates better than solid copper, a lot stronger too. I used 18 gauge speaker wire for my shortwave transmitter, worked great!
I think 5 Feet of that wire should be enough for FM as that would be about 1/2 wave I think. Good luck as I hope it transmits well for your complex.
Thanks for the info.
Is resistance a concern?
OK. Could you please expain how you quantified this?
As far as which wire radiates the best -- the difference for all practical purposes, between solid or stranded is immeasurable. Especially at the frequencies we're talking about. The difference is so slight it would take the best scientific instruments under very controlled conditions to measure.
Stranded is, however stronger and much easier to work with -- in long lengths -- e.g. ham radio and SW listening antennas many feet long.
Hence, for a self supporting, shorter FM antenna solid wire is the logical choice.
Odds are adding any antenna to a certified Part 15 transmitter will most certainly put it over the legal limit, unless you're starting out with a device way under the limit to start with (and most of the small $10 units ARE way under the limit, at least the one's I've tested).
TIB
Have to agree with post #6 on this topic and also repeat the question posed in post #5. Since it is so easy to meet (and exceed) the field strength limits on FM it seems unnecessary to worry about losses in the antenna wire. Here, I get the approximate expected legal range with a rigid telescoping antenna about a foot long which is attached to the transmitter board. Any more length yields a range which makes me nervous.
In your case, I would choose the antenna material for its mechanical and environmental suitability (corrosion resistance) with the simplest being insulated copper for outdoor use. For indoor use this wouldn't matter. It may be easier to get mechanical stability with solid wire if this is important but it is probably not in Part 15 FM operations.
Long wire antennas were mentioned earlier and though not a concern here such wire is usually copper clad steel where the copper gives conductivity and the steel gives strength. For many more dollars, hard drawn copper can be used but probably does not perform any better than CC steel.
Could be I have fellen victim to an old ham wive's tale. (Or maybe it is more important at different wavelengths?) The more I think about it the more silly it sounds. Stranded is a whole lot stronger without a doubt, less likely to snap since it can flex more comfortably. For antenna length calculations I use this tool quite often http://www.csgnetwork.com/freqwavelengthcalc.html
I also guess I overlooked exactly how the antenna would be constructed, I second the others opinion of using rigid copper for the antenna since it will be short and will need to be in a fixed position.
If you want to get really creative you could build a rigid antenna with PVC piping and 18 gauge wire, but part 15 FM is so limited any half decent antenna is going to exceed the limits.
I know of a couple of cases where the copper was shed off the steel wire. The wire then broke do to rust.