Some Newbie base antenna questions

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Sownman

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First if there is a document in Wiki I'd be happy to read it There doesn't seem to be anything that addresses the basic questions, or maybe I'm just trying to make things harder than they are. I've been following links in Wiki to manufacturers and reading posts
trying to learn. A couple questions....

When connecting a base antenna to a handheld scanner is it reasonable to expect new never heard signals ? Current poor signals to become good ? Current good signals to possibly need antenuation ?

Is Discone a type not a brand ? Is Super discone really "Super" ?

Can you use two antennas connected to one scanner ? I was looking
at the Cushfield for 40-50hz and some sort of discone for the rest of the range.
I have things in my area in the low 40 range but mostly I only need 100 and up.

Can you use more than two antennas to one scanner ? Are 5 identical antennas better than one ?

IF you can connect two antennas to one scanner do you need to avoid crossover
of freq. If you buy a specialized 40-50 and you combine with a 25-1300 do they mess
each other or the scanner up in the VHF lo.

Do different brands of 25-1300 antennas work better or is it just a construction solidity
difference ? You'll get pretty much the same thing from any 25-1300 $100 antenna
mounted in the same place with the same cable run ?

What is gain in an antenna ? Isn't that the idea, to supply additional gain to a radio ?
Why do some advertise gain and others claim unity gain or don't mention it at all ?

Transmit or recieve? Some antennas don't claim power handling capability others just seem to claim to be recievers. I am only interested in reception but is a transmit better or just more expensive or a non issue ?

From posts I've read it seems cable matters. Is more expensive always better ?
Does run length come into play ? For examble at 15' cable doesn't matter but at 60' it does ?

Thanks for any answers

Steve
 
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ka3jjz

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Let's try to answer these questions in groups;

a. Discones aren't really 'super' - that's a bit of overhype at best. They are very broadbanded antennas, usually defined to have no gain. Now, compare that to a typical antenna you get with your handheld scanner and you would find that the discone has some gain - not a lot, but just a bit. The typical duckie antenna is a compromise at best - having a good deal of loss at many freqs, and working just well enough to get some local stuff, and not much else. It should be pointed out that there are duckies that are 'tuned' to specific freqs, and these would perform much better (for example, the 2m/440 HT antennas for ham radios).

It is, therefore, quite possible, particularly if you live in an urban area, to overload a handheld when connected to a discone. A handheld is built to handle a very low level of signal - apply anything that might be higher, and all sorts of things can happen. Generally speaking, you might start hearing FM radio stations, pagers and other junk where it doesn't belong, or you might actually lose some sensitivity on frequencies. There are filters you can buy to handle most of these kinds of problems.

b. There are combiners/splitters that you can use to feed antennas, but there is a limit to how many you can combine - that's fairly complex math, but suffice it to say that more is not necessarily better, unless you are interesting in techniques involving making antennas that actually have some directivity and gain (phasing), and that is a whole 'nother discussion unto itself.

c. There are many brands of 25-1300 mhz antennas, and without empirical test results (which are not easy to come by), it's rather hard to say which one is 'better' than another. Due to many factors (not the least of which has to do with height above ground, the RF enviornment in which the antenna is tested, actual measurements at specific freqs, and many more) what performs well in one area may not do so well in another. You must consider an antenna as part of a 'system' - the radio, cable and antenna as a single operating unit.

d. Coax losses increase as you go higher in frequency, and both the length and construction have a role to play. Take a look at this chart, from one of the NASA ham clubs (anything in blue is a link)...

http://hamradio.arc.nasa.gov/coaxcableloss.html

Now the better cables do tend to cost more - but that's not a hard and fast rule. I saw a post just recently about someone finding some RG6 Quad cable at Wal Mart (!!)

e. Do not concern yourself with transmitting unless you are a ham or professional installer (i.e. doing work for a county or state..). For just scanning, it's pretty much a non issue.

Personally speaking I'd get a copy of the ARRL Antenna book and start reading. Best bang for the buck you can get when researching antennas.

Let the flames begin!

73s Mike
 

Sownman

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Santa Clarita Calif
Thanks for the answers and the book reccomendation. I'll try and find a copy. I wasn't really looking for a "better" discone (unless one really is) so much as verification that they are pretty much the same as long as mounted in the same place and being about same size and price. Example If I bought one and did not acieve my desired result I would know that butying another and mounting on the same mast is not goining to be massively different. If the first one doesn't work then I just out of luck. I'm equating it to TV antennas that I wasted a bunch of time and money with trying different models and different brands years ago to find you get no TV via antenna in my neighborhood.

Steve
 

ka3jjz

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Some discones like the Icom model have a whip that supposedly makes it work better in the 30-50 mhz range; but by and large, they are pretty similar. There are discones that are cut and tuned for various ranges - for example, AOR sells one (expensive) just for the 700-800 mhz area, I think. 73s Mike
 
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