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How high does an antenna really need to be?

 
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How high does an antenna really need to be?
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Casey
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Post How high does an antenna really need to be? Reply with quote
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?
Mon Jan 17, 2005 10:06 pm View user's profile Send private message
pcs
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Simple: The higher the better.

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Tue Jan 18, 2005 12:17 am View user's profile Send private message Visit poster's website
Sir Nigel
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Post Re: How high does an antenna really need to be? Reply with quote
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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Tue Jan 18, 2005 12:49 am View user's profile Send private message Visit poster's website
pcs
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What would I do without you, Nigel

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

PS: Have you heard from radioboy?

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Tue Jan 18, 2005 12:35 pm View user's profile Send private message Visit poster's website
Casey
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Post Reply with quote
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?
Tue Jan 18, 2005 2:55 pm View user's profile Send private message
pcs
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Post Reply with quote
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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Tue Jan 18, 2005 4:07 pm View user's profile Send private message Visit poster's website
Casey
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Well, that makes sense, but is a dipole necessarily a "bad antenna", or is it just more suited for a lower power station?
Tue Jan 18, 2005 4:39 pm View user's profile Send private message
pcs
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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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Tue Jan 18, 2005 5:12 pm View user's profile Send private message Visit poster's website
Casey
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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.
Tue Jan 18, 2005 7:30 pm View user's profile Send private message
Sir Nigel
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Post Reply with quote
Either the proven Comet or the newer one here:

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


Inconspicuous? Well, it is an antenna so it will be conspicuous. perhaps you could put some shrubs around it. just kidding.

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Wed Jan 19, 2005 12:14 am View user's profile Send private message Visit poster's website
pcs
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hmm, you could put the whole thing in a plastic tube maybe and
attach it to a chimney or something.

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Wed Jan 19, 2005 1:25 am View user's profile Send private message Visit poster's website
Casey
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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.
Wed Jan 19, 2005 8:01 pm View user's profile Send private message
woodro
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Post Reply with quote
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

comments?
Thu Jan 20, 2005 3:01 am View user's profile Send private message
pcs
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Post Reply with quote
Remember, same antenna can and is used for FM reception
so that's what you can allways claim.

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Marko - PCS Electronics
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Thu Jan 20, 2005 9:54 am View user's profile Send private message Visit poster's website
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