"Al Klein" wrote in message
Four things you should be aware of:

1) A discone is a negative gain antenna - that is, it has less gain
than a dipole, which is the standard by which 0 gain is measured.
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Name 1 "scanner" antenna that does have gain? Not an
amatuer antenna a "scanner" antenna. NONE, have any gain.
If you want to use a amateur antenna as in a dual band, fine.
But its going to operate in negative gain territory outside of its
design limits also. Not many people want to listen to just 2 areas
of the spectrum, i.e. 146Mhz and or 440Mhz. With trunking a
fact of life nowdays most people want to listen anywhere from
100 to 900Mhz. There are only 2 antennas that work well all
the way thru that area, one is the discone and the other is the
Austin Ferret. With the Ferret running at 225$ most people dont
want to spend that much.

Since the signal it receives is so weak, the cable is VERY important -
the lower the loss the better, even if it's a fairly short run. DON'T
buy your cable from Radio Shack - they don't sell any low loss cable -
only cable that's lowER loss than the regular cable. Go to this site
http://www.timesmicrowave.com/cgi-bin/calculate.pl, plug in the
highest frequency you're interested in (will you be listening to
850?), the cable type (try a few of the common ones - RG6, RG8, RG58)
and the approximate length of cable, and you'll see how much signal
the cable will lose. Look at the "efficiency". Subtract that from
100 and that's how much signal is being lost.
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Actually a nice link, very informative and agree with it
totally. I use Quad Shielded RG 6 with only about a 25' run. Im good
up to about 1 Gig. Not much above that to listen to anyway.


Be prepared to spend at least 50 cents/foot for decent cable and up to
$2/foot for good cable. Putting up a gainless antenna and lossy cable
(like 100 feet of RG58 for 850 MHz - 96% of the signal is lost in the
cable) is just a waste of time and money. You'll probably receive
better with a rubber duck on the scanner.

2) Don't buy hype, buy an antenna.

If a discone is designed properly, and very well made, it will cover a
frequency range of 4:1. (Most real - not on paper - discones are more
like 3:1.) The lowest frequency is that at which the radials are 1/4
wave long. So to receive VHF-lo well they have to be about 6 feet
long. The highest frequency this antenna will be any good at will be
about 120 MHz.
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Actually a good discone is closer to a 10: 1 ratio. Most, without
the vertical stinger are good from 100-1000Mhz. I have transmitted
on mine on 52, 144, 440, and 904Mhz with anywhere from excellent
to good results. ( mine does have the stinger) Actually mine works
very well in the 900Mhz area in general, better than any other scanner
antennas I have used, and I have had them all up at one time or another.
Scantenna, Scan King 1500, various Antenna Specialist scanner antennas
and most of them were almost deaf in that range.

The typical discone with 3 foot radials will cover from about 75-225
MHz.
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The math for a discone is totally different than the math for
a dipole. They just dont work the same way.


3) Wherever you put the antenna, and no matter how high you put it,
figure out where it will fall if the mount breaks away at the base. It
should fall within the confines of your property - for a few of
reasons.

Agreed

Add last, but by no means least, if you're going to put up an outside
antenna, PLEASE put in a good grounding system, ground the mast to it
and use a static discharge device on the cable. The ground system
should tie ALL the grounds in the house to one point - telephone,
electric, antenna. And a decent ground (not a good one, a decent one)
is AT LEAST 4 10 foot ground rods spaced in a rectangle at least 10
feet on a side, with wire going from 1 to the next, but NOT forming a
loop, with all your grounds connected at one point along that run -
any one point, preferably near the middle.
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You're getting carried away here again with the grounding thing.
Nobody, and I mean nobody puts a grd system in as you describe here.
It simply isnt needed.

I'm not making this up - read the National Electric Code on grounding,
or ask an electrician. This is important - people are killed every
year by bad antenna installations. Not many - but if you're one of
them, it doesn't matter how many there are.
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The people that do get killed are the idiots that put up a mast
and an antenna 10' from a power line, and when it goes down and lands
on a power line bad things happen. Rule No. 1, do not put ANY
antenna even remotely close to ANY power line and you wont have
any problems.