dual base antennas

[casper9]

is it possible to set up 2 base antennas? the reason im thinking about this is because i dont want the antnnas to raise about the house to much, and where my house is located, i just need them rx and tx in 2 directions. its probably hard for me to explain what im trying to get at, but for simplicity sake, how could i go about setting up 2 antennas to work at the same time on 1 radio?

['Doc]

The quick-n-dirty answer is that you'd do it the same way you would for a mobile, with a couple of exceptions. Those exceptions deal with the distance between the two antennas and the lengths of the phasing lines.
Since the possible distance apart of a mobile system is usually less than what's available with a base installation, you can increase that distance and realize a little gain from it. Not a big increase in gain, just some. That other 'exception', or difference in in the lengths of the phasing lines.
So what's a 'good' distance? Try something on the order of 18 feet instead of the typical 9 feet for a mobile (half wave length instead of 1/4 wave length). That assumes that you've got that 18 feet in the right direction in your yard. Don't have 18 feet of room in that right direction? Use 9 feet instead.
Rather than go through all the typing, I would suggest finding a copy of the 23rd edition of the "Radio Handbook" by William Orr (W6SAI), which has a very nice and simple explanation about it on page '22-7' and there abouts. Don't know about the earlier/later editions, but that one certainly has it in there. [Published around 1997, not easy to find probably. Not a bad book to have around, LOTS of stuff in there that's really nice to know, and much easier/simpler than the ARRL's Handbook. (Beg, borrow, buy, steal the @#$ thing! Well worth it.)]
Phasing lines, or how to 'time' how far the signal has to travel so that it gets to both antennas at the right time (definition of 'phasing' in this case). This is where 'velocity factor' of coax comes in. Typically means you end up with feed lines that aren't quite long enough to reach between here and there, so it's nice to know about the characteristics of particular lengths of coax phasing lines. One of those characteristics is that electrical 1/4 wave lengths tend to change things, electrical 1/2 wave lengths tend to keep things the same. Or, another way of saying it is that 'odd' multiples of a E1/4 wave length can change the impedances, 'even multiples don't change impedances. You either see the same impedance on one end as the other end, or it changes. Your eyes getting glazed over yet? Hang on, you ain't got to the good part yet!
Coax cable isn't exactly the most 'exacting' stuff in the world. There are differences in it's characteristics on the same 'roll' of it, much less in separate 'batches' of it. It's made by man so it ain't gonna be 'perfect' by any means. That means that you can't take it's stated characteristics for granted. You either have to measure them yourself, or do some experimenting to get that 'perfect' length for phasing. Just going by the advertised 'numbers' you can only count on getting 'close', 'perfect' is one'a them miracle thingys.
Are they 'glazed' yet, your eyes I mean? It's not all that difficult and I'm certainly not trying to discourage you! There is more to it than you might think, though, and this is just sort of a 'heads up'.
- 'Doc

Pssst - Get that book!

[TwentyTwo-Zero]

Until you get that book (and get it if you can) here is an article that will give you an idea of what's involved:

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[casper9]

thanks for all the good info. i checked out that page and it looks like a lot of work. haha but its still something to consider.

[casper9]

i just bought the book online, $50! used. suppose to be in good condition (ex-library book), its probably a really good book if its selling for that much. there were new ones for 100+ bucks. well should be here May 4th or so.

['Doc]

$50 - $100 dollars... You're kidding, right? You're not kidding! ... Hmm. What would you give for an autographed copy in very good shape??
- 'Doc

(Is it really autographed? @#$$ no! But it will be by the time you get it!)

[casper9]

well i was looking for something in decent condition and a hard cover, plus i dont think that the 23rd edition is being printed anymore so its more of a rare book i guess. but 50 bucks isnt to bad if the info is worth it, ill tell you that when i get it!

['Doc]

Lets see if this works.

Copied from that 23rd edition. Slightly modified with colors. NOT enough information to do any phasing without the rest of it! But, just an example of 'wazinda' book.
- 'Doc


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[TheCBDoctor]

Hi casper9

For something so simple as an antenna there is a lot of theory behind it. Marconi is known for the invention of the radio, but worked out the principles for the development of the antenna. If you ever visit Cape Cod you can see what is left of the supports that supported his trans-Atlantic antenna that is slowly being swallowed up by the sea.

It was the first antenna used that sent a radio signal across the ocean to England. One thing about dual antennas is the affect it has on the direction and the shape of the signal pattern. If the antennas are too close it may cause a figure 8 pattern if they are place haphazardly the signal from one antenna may be canceled by the other. Frequency and the distance between the antennas is critical.

There is a local radio station that is near Long Island Sound. Two antennas are placed at a specific distance apart for the sole purpose of canceling the signal that would cross the sound. In effect a beam antenna is created that allows the signal to run along the coast, but not in a southern or northerly direction. You can fill a book on what is the physics behind a single antenna never mind using more than one on a single feed.

[casper9]

ya it just sounds to difficult. i think ill be happy with a single antenna

thanks for all the info, that trans-Atlantic and beam antenna is real interesting