antenna cost estimation

Around $250

What kind of transmitter is this for?

(Hey, there's an echo in here...)

Bruce, The Dog Radio Group

I think it is important to know what kind of transmitter you want to use with the antenna.  Because there are other options rather than building an antenna - you can pick up a ProCaster with built-in antenna, or a Rangemaster which uses an inexpensive whip, or even a Talking House with an ATU which uses a whip as well and get that 1/2 mile (sometimes even up to a mile, or more) range you're looking for.  It all depends on what your limiting factors are, such as cost, or ease of installation, audio quality or ??

10 foot 3/4 copper pipe, endcap and threaded adapter, assorted PVC fittings and pipe, copper magnet wire, assorted hardware and a couple connectors?  Can't see how you can spend more than $100 if you do it yourself?

I want to build a Folded dipole to replace my Ice Damaged FM transmitting Antenna.  I have 1/4 aluminum rod and a shop full of tools.  What I am missing it seems is intelligence.  Every time I start to try and calaulate this it comes to 5 of 6 foot of metal yet the old one is just about three feet.

I broadcast at 87.5 FM.  I would like to have a set of instructions that tell me where to put the curves, how long  etc, I guess basicly I am asking how do I build one of these things.  Can anyone point me in the right direction  or even better tell me what to do.  I am not radio savey, but I can use a hammer:-)

Ian

The length of a folded dipole antenna should be electrically 1/2 wavelength at the operating frequency. Here's a way to calculate this:

Half Wave Length (inches) = 5905 / frequency in MHz

So for F = 87.5 MHz the half wavelength is = 5905/87.5 = 67.5 inches. Generally, to allow for the wavefront speed on the antenna being less than the speed of light this length is multiplied by 0.95 so L = 0.95 X 67.5 = 64.1 inches.

I don't know why your original was shorter unless it wasn't a half wave antenna.

As far as construction, do a web search on "half wave folded dipole antenna" and you will find lots of articles about this.

Neil

There is no radiation advantage to a folded dipole vs. just a plain dipole. The difference between the two configurations is the feed point impedance. A folded dipole is 300 ohms and a dipole is 75 ohms. Both antennas are 1/2 wavelength total length which can be calculated from Neil's post.

Assuming you want to feed the antenna with 75 ohm coax, you should construct a dipole, not a folded dipole.

Orienting the dipole vertically will produce an omnidirectional pattern, which is better suited to broadcasting.

A vertical dipole should be constructed using tubing or pipe for the lower element to allow you to pass the coax up inside the bottom element to the center point. Either tubing or rod stock can be used for the top element. At the center, the coax shield should be bonded to the bottom element and the center conductor bonded to the top element. See http://www.alpharubicon.com/elect/vertdipoleniet.htm for an example.

When mounting a vertical dipole on a supporting pipe (mast pipe), the bottom dipole element should be insulated from the mast pipe. Ideally, the bottom element should be mouted at the top of the mast pipe with some sort of insulated coupling between the element and the mast pipe. A less desirable, but usable alternative is to clamp or screw the bottom element to the top of the mast pipe with maybe a foot of overlap for stability. If you dp this, there is no electrical contact between the bottom element and the mast pipe.

The question of estimating the cost of an antenna is on my mind today because I want a 50-foot tower in the backyard.

Under the rules 50-feet is allowed for long wave Part 15 at 1-Watt, and that's where we want to go.

It would need to be an insulated tower, installed professionally, and might be fairly costly.

Local ordinances are unknown at this time, so we either need to research them or just wait for a take-down notice if we go ahead and gamble.

But even more concern is the likely backlash from neighbors who have peculiar religious prejudice against towers.

What we really need is an invisible tower, maybe a fine length of wire held up by a remote controlled toy helicoptor.

Not helicopters (you'd more likely want one of the 4-rotor photo platform drones), but balloons. In Africa, some of the stations which got their antenna towers blown up by paramilitary warlords got right back on the air by launching weather balloons with wire antennas. Must have had a cache of them kept camouflaged somewhere close by.

If you have a ham license, you can have your 50' tower, but otherwise local ordinances will probably disallow it. You can sometimes find short towers taken down and left. Or you could build your own with pipe and guys.

BTW, what on Earth does religion have to do with this? Sorry, I don't get that.