Hi Scott

There are many types of Discone antennas available depending on what
frequency range your interested in receiving. Cable is a very
important consideration and often overlooked. When I purchased the
Icom AH-7000 Discone antenna, about twelve years ago, a fifty foot
section of their so called "low loss" cable was included, and
terminated with "N" connectors at both ends. Personally I wouldn't
even give that included cable away to someone I didn't know, as it is
pretty poor quality.

When this particular Discone was installed, the cable I selected was
Belden 9913. This cable has a 9 1/2 AWG solid center conductor, a
solid spiral teflon tube continuously running around the center
conductor which is enclosed in a air dielectric teflon tube bonded with
copper foil on the outside and that is covered with a braided copper
shield and covered with a soft PVC water-proof jacket. There is an "N"
connector with the center pin specifically made for this exact cable.

Since this cable is not as flexible as some installations may require,
"Cable Experts" has a "9913" equivalent cable which is a little more
flexible, it's "CXP1318" and is available in various lengths terminated
with either an "N" or "PL-259" connector.

Believe it or not, the difference in this cable compared to the cable
included with the Discone was significant. This test was made with the
Icom AH-7000 Discone using equal lengths of both cables, fifty feet,
and both cables were terminated with type "N" connectors. Using my
Icom IC-970H multi-mode transceiver, I observed about SEVEN S units in
signal strength at 432Mhz. That's right, SEVEN! I now have a twenty
two foot section of "Andrews Heliax" hardline cable connected to a
"KB6KQ 432Mhz loop antenna". Realizing I'm getting off topic here, the
point I'm attempting to make is the CABLE is a VERY important issue!

May I suggest that before you finalize your anticipated antenna
installation, do some testing with antenna placement, you may find that
it may not be necessary to have it mounted outside in the weather. I'm
located right on the beach and routinely need to remove, clean and
replace my Discone every few months due to corrosion. This next week
I'll be purchasing the AOR DS3000A Discone antenna. This will be
mounted inside with only a six foot section of CXP1318 cable and
dedicated to the Uniden BC796D I purchased just last week. Believe it
or not, it is my very first "scanner".

You may even have an area in the attic which will accommodate your
installation. I say this because when you start installing antennas
outside, sometimes your neighbors suddenly become interested in what
your doing. Something else you may want to consider. My nearest
neighbor is probably less than a mile away, so I do not worry about
this and have various antennas mounted outside only because their also
used for transmitting as well.

If you do not plan on using your Discone for transmitting you may get
away with it mounted inside. Above all, use good cable and if possible,
keep cable lengths to a minimum!

Best regards

george



On 2005-10-29 12:12:53 -0700, Al Klein said:

On Fri, 28 Oct 2005 14:30:45 -0400, Scott said in
rec.radio.scanner:

Could someone really help a newbie out on what i would need to buy to get
this antenna just right for scanning. I'm not afraid to do anything,
but seriously just don't know what all I need, and what i should
expect from this type of setup.

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.
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.

Don't let anyone tell you that it only matters if you're transmitting.
Do you see any "direction" choice there? The same amount of signal is
lost in both directions. (Actually a little more is lost with a
scanner because the scanner isn't a 50 ohm load to the cable.)

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.

The typical discone with 3 foot radials will cover from about 75-225
MHz.

25-1300 MHz is advertising copy, not measured performance. If anyone
can get a discone (without a whip sticking up on top - just a pure
discone - if you want whips, buy a Scantenna, or something like it) to
cover a 50:1 frequency range (25-1300), you're going to hear him named
a Nobel prize winner in physics. And science will have to be
rethought.

ANYTHING that's not an insulator will receive signals. The question
is whether that thing, at the end of some reasonable length of
affordable cable will receive any more signal than an antenna plugged
right into the scanner. Why put up an antenna that gives you 6db gain
over the antenna on the scanner and connect it with cable that gives
you 9db loss? You just REDUCED the signal you're going to hear by 50%
(3db). Sure the antenna has 6db gain over the one on the scanner -
but it's not going to do you any good unless the cable loss is less
than 6db.

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.

1) You don't want a neighbor getting hurt if it falls.
2) You WILL be considered legally negligent if you mount it so that it
can fall outside your property line.
3) Your insurance won't cover the judgment against you - you'll pay it
all out of your pocket.

But don't mount an antenna on your chimney. Aside from the fact that
a chimney isn't made to withstand the torque produced when the wind
hits the antenna, part of what goes up the flue is sulphur and, when
it comes into contact with water (like from air with any humidity at
all), it forms sulphuric acid. Do you really want your antenna bathed
in that for months at a time every year?

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.

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.

With all that in mind, this is a hobby, so enjoy it.

On Fri, 28 Oct 2005 14:30:45 -0400, Scott wrote:

What could I expect from an outdoor Antenna? I have nothing to attach
an antenna to on my roof. I'm newbie at this, and was curious as to
how hard it would be to install this

Just use a 1/4 wave VHF whip (unity gain on VHF, 1/2 wave gain on
UHF) and some decent quality RG6X quad shield satellite cable. Put
the whole thing on a short mast on your roof, use an "F to PL259"
adapter on the antenna end, and an "F to BNC" adapter on the scanner
end inside.

Should give you PLENTY of improved performance over a duck.

Discones are very low gain and wide band. They also bring in a LOT of
unwanted interference with intermod/etc.

You'll do fine with a VHF 1/4 wave as a base station antenna for
scanner use.

The impedence mis-match of the cable won't make a whole lot of
difference to the scanner.

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 Sun, 30 Oct 2005 14:30:00 -0800, Limited Viability
said in rec.radio.scanner:

Just use a 1/4 wave VHF whip (unity gain on VHF, 1/2 wave gain on
UHF)

Minor point - 1/4 wavelength at 150 MHz is 3/4 wavelength at 450 MHz.

Discones are very low gain and wide band. They also bring in a LOT of
unwanted interference with intermod/etc.

Being broadband, they bring in signals that may cause intermod, but
that can't "bring in intermod".

You'll do fine with a VHF 1/4 wave as a base station antenna for
scanner use.

Better than with a discone, but not for more than 2 bands - 150 and
450 - or 1 band of his choice.

The impedence mis-match of the cable won't make a whole lot of
difference to the scanner.

It won't make any difference to the scanner - the load doesn't care
about impedance mismatch.

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:

One thing you could do is attach a 5-foot mast to your chimney with the
chimney mount kit from Radio Shack. It's easy to mount the discone to that
mast. If you can figure a way to get the feed line into your house (through
a gable vent, for example), you could expect to get great results as
compared to a handheld or desktop antenna.

I installed the 19-foot telescopic mast to my deck with a fixture that
allows it to be tilted down (all hardware from Radio Shack). Since I was
into ham radio at that time, it allowed me to install different antennas to
try out. The deck is elevated, so I can get the antenna up about 25 feet
from ground level without ever having to climb on the roof or installing guy
wires. The first antenna I used was the RS discone, which worked very well.

- Doug


"Scott" wrote in message
...
What could I expect from an outdoor Antenna? I have nothing to attach
an antenna to on my roof. I'm newbie at this, and was curious as to
how hard it would be to install this

http://www.radioshack.com/product/in...rs&tab=support

Years ago my neighbor was a cb freak, and he had a freaking tall
antenna on his roof. How would I get this up high enough? Could
someone really help a newbie out on what i would need to buy to get
this antenna just right for scanning. I'm not afraid to do anything,
but seriously just don't know what all I need, and what i should
expect from this type of setup.