"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.
-------------------------------------------------------------------------------

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.
--------------------------------------------------------------------------

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.
------------------------------------------------------------------------------

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.
--------------------------------------------------------------------------
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.
---------------------------------------------------------------------------

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.
--------------------------------------------------------------------------------

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.

On Sun, 30 Oct 2005 15:27:34 GMT, "Jeff"
said in rec.radio.scanner:

"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.

Name 1 "scanner" antenna that does have gain? Not an
amatuer antenna a "scanner" antenna.

Since we never covered "scanner antenna" in antenna theory, define
what you mean.

Dipoles (or ground planes) have, by definition, 0dbd gain. A discone
has negative gain, vis-a-vis a dipole.

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

The discone operates, at best, over a 4:1 frequency range, not exactly
VHF-hi to 850.

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.

I'll go along with 2.3db loss being ok, but what is quad shielding
buying you with an unshielded scanner?

Actually a good discone is closer to a 10: 1 ratio.

When are they awarding you your Nobel prize?

Most antenna engineers will quote you 3:1 for real world antennas.
Some claim that they can actually achieve 4:1, but I suspect the
machining costs would make the antenna unaffordable.

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.

I can do the same thing with my R7, but that doesn't make the antenna
an antenna at those frequencies. Conductors don't accumulate signal,
they radiate it.

The math for a discone is totally different than the math for
a dipole. They just dont work the same way.

Yep - the rule of thumb is that the lowest frequency is that at which
the radials are 1/4 wave and the highest frequency is 3 times that for
a good design that's been well implemented.

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.

No one you know - okay. Many people I know have and do.

It simply isnt needed.

Not unless you want a good ground. I'm not talking about not having
the mic bite you, I'm talking about not living in a hole in the ground
after the pole pig on the pole in front of your house suffers a direct
strike.

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.

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.

I'm talking about those killed by lightning. You don't run a ground
system to blow breakers on a 440 line that are located a few miles,
and a few transformations, from the ground.

Rule No. 1, do not put ANY
antenna even remotely close to ANY power line and you wont have
any problems.

Until the clouds gather.

I hope you sleep well when someone actually takes your advice and it
results in his death.

*N*E*V*E*R* take *A*N*Y* chances with lightning. 50 million volts
can't be "handled" by anything man can do when it has tens of
thousands of amps available behind it.

On Mon, 31 Oct 2005 05:57:39 -0500, Al Klein
wrote:

On Sun, 30 Oct 2005 15:27:34 GMT, "Jeff"
said in rec.radio.scanner:

"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.

Name 1 "scanner" antenna that does have gain? Not an
amatuer antenna a "scanner" antenna.

Since we never covered "scanner antenna" in antenna theory, define
what you mean.

Dipoles (or ground planes) have, by definition, 0dbd gain.
Incorrect, gain is normally quoted over an Isotropic radiator, which a
Dipole is NOT. However relative to an isotropic radiatior, and
Discone is a zero gain antenna. The attraction of the Discone is from
the low VSWR over vast frequency range. A very high VSWR can turn a
high gain antenna into a losing proposition because of feedline
losses.

A discone
has negative gain, vis-a-vis a dipole.
T

On Mon, 31 Oct 2005 17:26:18 -0700, matt weber
said in rec.radio.scanner:

On Mon, 31 Oct 2005 05:57:39 -0500, Al Klein
wrote:

Dipoles (or ground planes) have, by definition, 0dbd gain.

Incorrect, gain is normally quoted over an Isotropic radiator, which a
Dipole is NOT.

Normally advertising hype is quoted in dbi, while honest antenna gain
is quoted in dbd. So is engineering gain.

Antennas are my field. What Mr. Klein says about the useful frequency range
of a discone antenna is right. A reasonably well designed discone antenna
will have about a 3:1 frequency range because the pattern degrades as the
frequency increases. It is also true that the SWR of a discone usually
remains under 2:1 for a significantly wider than 3:1 frequency ratio. Of
course, SWR is no measure at all of an antenna's performance.

Another example of an antenna with a far larger SWR bandwidth (to coin a
phrase) than pattern bandwidth is the terminated rhombic antenna. A well
designed rhombic has 2:1 or perhaps 2.5:1 pattern bandwidth and a huge SWR
bandwidth.

When doing propagation measurements in West Va. over 40 years ago, I
came across a small rhombic in a front yard being used to receive TV
signals. The man of the house had been in the Signal Corps.

One last note: almost anything will "work" as an antenna. The issue
should be how well does the antenna work, never whether it works.

Regards, Mac

..... slowly finding some of the "secret instructions" of my brand new
BCD396T.

--
J. Mc Laughlin; Michigan U.S.A.
Home: