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.
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