How high does an antenna really need to be?

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Casey
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How high does an antenna really need to be?

Post by Casey »

We want to be able to broadcast at either 5W, and get 3-4 mi as per the newbite guide, or go to 15W and go out to 6 mi. Haven't decided yet.

But we live in a 2 story house surrounded by other 2 story homes. It's a new subdiv so there's no tall trees around. Standing on the roof all you see is more roofs, in every direction (except the local park, about a mile away.)

What I want to know is, how high should our antenna be to get these distances? We live in a pretty flat area, so the earth's curvature formula says that you only have to be about 6 feet up to see a horizon of 3-4 mi. Would an antenna 10ft above the roof be enough?

Also, if the antenna itself is ~5ft tall, should the base of the antenna be where we measure to?
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Post by pcs »

Simple: The higher the better.
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Re: How high does an antenna really need to be?

Post by Sir Nigel »

First, just go with 15 watts. The extra watts will help get into the houses better.

As far as the antenna, maybe just a little more than 10 ft. You want the signal to go above the houses, not through them as that doesn't work. However if you have a choice of higher antenna vs. higher wattage, I would go with making the antenna taller.
Casey wrote:Also, if the antenna itself is ~5ft tall, should the base of the antenna be where we measure to?
Yes.
Casey wrote:We live in a pretty flat area, so the earth's curvature formula says that you only have to be about 6 feet up to see a horizon of 3-4 mi. Would an antenna 10ft above the roof be enough?
Likely yes, but remember, houses are going to block the signal, so adjust your "imaginary" horizon to compensate.
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Post by pcs »

What would I do without you, Nigel :)

By the way, I gave you a special rebate for the RDS card. :D

PS: Have you heard from radioboy?
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Casey
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Post by Casey »

Thanks for the replies!

Follow-up question: Given that the antenna will need to be over 10 ft off the roof, and that might be a little conspicuous in the neighborhood, I'm wondering, what's the best antenna for me if 15W is the most I'm ever going to transmit at?

I looked at the comet, and although it's quite nice, it might be more antenna than I really need (given that it's rated for up to 200W). What I want is an antenna that's sufficient for a nice clean signal at 15W, and not much more. I was wondering whether a dipole would be sufficient for this? Any suggestions?
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Post by pcs »

Power rating does not mean that antenna is "too strong" for you.

What's important here is how far do you actually want to go.

more power + bad antenna = less power + good antenna

less power + bad antenna = minimal range
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Post by Casey »

Well, that makes sense, but is a dipole necessarily a "bad antenna", or is it just more suited for a lower power station?
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Post by pcs »

It is antenna with less gain compared to 5/8 and 3/4 wave or
yagi antennas.

Another problem is proper balanced/unbalanced conversion.

Since dipole is balanced and coaxial cable is not. So just using
two sticks of proper length is not enough.
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Post by Casey »

What antenna would you recommend for a person who is looking to broadcast at 15W, reach a range of ~5-6 miles, and wants an antenna that is inconspicuous?

Maybe that's how I should have phrased the question from the beginning.
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Post by Sir Nigel »

Either the proven Comet or the newer one here:

http://www.pcs-electronics.com/phpBB2/v ... php?t=1017


Inconspicuous? Well, it is an antenna so it will be conspicuous. perhaps you could put some shrubs around it. :roll: just kidding.
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Post by pcs »

hmm, you could put the whole thing in a plastic tube maybe and
attach it to a chimney or something.
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Casey
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Post by Casey »

Well, less than being concerned about hiding the antenna altogether, I was more thinking about having something that didn't scream FM transmitter to nosy people. But more importantly, as I said above, since I don't expect to ever transmit greater than 15W, I don't want to buy an antenna that is more than I need. So I'm looking for an antenna suggestion that would be sufficient for broadcasting at that wattage.

Clearly the Comet is better than a simple dipole, and the high-gain is better than the Comet. But are they more than I need? That's what I'm trying to figure out. The smaller or less obtrusive the antenna is, the less likely I am to get the neighbors curious.
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Post by woodro »

just a thought. An antenna designed or that looks somewhat like a tv antenna would be nice :) kinda incognito

micro yagi? Directional yes but with a small rotor it would keep a spin on things, maybe even a little harder to hunt down\zero in on especially at <15w

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Post by pcs »

Remember, same antenna can and is used for FM reception
so that's what you can allways claim.
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