Al Klein schrieb:

On Sat, 30 Oct 2004 11:55:50 +0200, Volker Tonn
said in alt.radio.scanner:


Al Klein schrieb:

On Fri, 29 Oct 2004 22:45:21 +1000, "Troy R."
said in alt.radio.scanner:


They don't seem to know much about it. Discones aren't resonant
antennas, but they do pick up signals from the design frequency to
daylight..


Not having read the linked page....
Discones ARE resonant on an extremly wide range.
Therefore they have nearly no gain above the (theortical) isotropic
antenna. This means they have a loss of around 1/2 S-unit against a
dipole or a half-wave vertikal antenna on a specified frequency. Not too
bad for a compromise.
The resonant range of a well designed and built discone is spread 1:10
on wich you can transmit. This is 50 to 500 Mhz or 100 to 1000Mhz for
example, covering the most wanted frequencies for scannists and is also
usable on ham-bands or FRS to transmit.


We're using different definitions of "resonant". The definition I use
says that an antenna can only resonate on a frequency. (Pretty much,
the frequency a dip meter will indicate when coupled to the antenna.)
It can have a bandwidth over which it can be used, but the resonant
point is (usually) one single frequency. Discones look like dipoles
with the 2 legs being different lengths, so the best one could say -
using my definition - is that they "resonate" on the frequency at
which the disc is 1/2 wavelength in diameter and the frequency at
which the cone element length is 1/4 wavelength.

To say so, a discone has it's "middle frequency". But impedance curve
stays constantly over a very wide range around. So in theoretics you can
get a frequency modulated signal with center frequency of let's say
500Mhz and a bandwidth of 800Mhz through a discone with a straight power
curve wich has no loss by mismatching of the antennea.
I don't know of any TRX providing such a signal :-)

As I understand the principle of a discone the disc is a load plate wich
spreads the bandwidth in conjunction wich the conical "antenna wire". So
the "resonant" wavelength is more related to the length of the cone
measured from the the top plate in 90 degree angle to the bottom.
You may correct me if I'm wrong :-)
Have a nice weekend.

So after all that is someone out there going to answer the original question
which was basically (Is the scanmaster airband discone that nevada sell
worth it's price tag) rgds all from M3PAC.... PAUL.....
"Troy R." wrote in message
u...
I am after a good V/UHF airband antenna and found this on a Google search.
Anybody actually own one and can tell me how they perform?

http://www.nevadaradio.co.uk/acatalo...airmaster.html

--
Regards
Troy Rowland

Perhaps

a) Nobody on this NG uses it, or
b) Any that do use do not think it worth commenting on.

Possibly the "silence speaks volumes".

Marco
(Who uses a Diamond D707)


"paul churchill" wrote in message
news
So after all that is someone out there going to answer the original question
which was basically (Is the scanmaster airband discone that nevada sell
worth it's price tag) rgds all from M3PAC.... PAUL.....
"Troy R." wrote in message
u...
I am after a good V/UHF airband antenna and found this on a Google search.
Anybody actually own one and can tell me how they perform?

http://www.nevadaradio.co.uk/acatalo...airmaster.html

--
Regards
Troy Rowland






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"paul churchill" wrote:

So after all that is someone out there going to
answer the original question which was basically
(Is the scanmaster airband discone that nevada sell
worth it's price tag) rgds all from M3PAC....

Being an antenna nut and regular listener to aircraft
communications, I, too, would like to know.

I presume you mean this antenna:
http://www.nevadaradio.co.uk/acatalo...airmaster.html

It is sort of a bi-cone antenna and sort of
a "dipole cluster" antenna.

The same basic idea (dipole cluster) is used in the
Antennacraft Scantenna ST-2:
http://www.grove-ent.com/ANT7.html
but this one is not optimized for the aircraft bands.

The discontinued Channel Master 5094A Monitenna
is much the same and has proved to be a good
monitor antenna for me for the "public service"
bands. It, too, is not optimized for the aircraft bands

The Scanmaster Airmaster should work pretty
well just by looking at it but one never knows until
they are in place and operating.

I created and moderate and aircraft listener's group
http://groups.yahoo.com/group/AirCommSouthwest/
of nearly 600 members and I posted an inquiry
about the Scanmaster Airmaster but apparently
no one has had experience with one, though the
inquiry did start and aircraft monitoring antenna
thread.

One problem in the U.S. is that no one seems to
sell the Airmaster, at least, I can't find a retailer.
One may be able to buy them from the U.K.
though.

I did buy a so called "Double Discone" (bi-cone)
on eBay and have yet to try it but it looks like
one could make and Airmaster out of it by
cutting the elements. It would be nice to have
the element dimensions from the Airmaster.

Here is a description of the "Double Discone:"
http://www.radio-ware.com/products/ant426.htm

Here is another option:
http://www.ssejim.co.uk/vhfairbandant.htm
http://www.ssejim.co.uk/uhfairbandant.htm
http://www.ssejim.co.uk/dip2002abeu.htm

I did buy the last item from the U.K. and it seems
to work well. I have separate antennas for
VHF and UHF aircraft and then combine them
into a single coax feed.

Another option to combine VHF and UHF aircraft
antennas would be the CF-142:
http://www.cometantenna.com/products...=23&childID=44

Iden - Northern California

YES THE SCANMASTER AIRBAND DOUBLE DISCONE WORKS WELL.

But you could make one for a few pounds.

Dual or Tri-band band amateur antennas have internal matching networks
which can give poor results when used outside their intendend
frequency ranges.

They can work reasonably well upto approx. +/- 20% outside their
design frequencies (plus a few odd harmonic resonses), which may be OK
for PMR monitoring. But it will not provide good coverage of the whole
of the UHF MIL air band.

I use a Double discone and can monitor re-broadcast satcom traffic in
the UHF Mil band, so I think it is good enough.....

UKM

"paul churchill" wrote in message ...
So after all that is someone out there going to answer the original question
which was basically (Is the scanmaster airband discone that nevada sell
worth it's price tag) rgds all from M3PAC.... PAUL.....
"Troy R." wrote in message
u...
I am after a good V/UHF airband antenna and found this on a Google search.
Anybody actually own one and can tell me how they perform?

http://www.nevadaradio.co.uk/acatalo...airmaster.html

--
Regards
Troy Rowland

"Troy R." wrote in
u:

Hi Troy, I used to have one, it worked fine for about 1 year then it got
broke. Dunno what was wrong with it though.

I am after a good V/UHF airband antenna and found this on a Google
search. Anybody actually own one and can tell me how they perform?

http://www.nevadaradio.co.uk/acatalo...airmaster.html

"Henk" wrote in message
. 2.2...
"Troy R." wrote in
u:

Hi Troy, I used to have one, it worked fine for about 1 year then it got
broke. Dunno what was wrong with it though.

I am after a good V/UHF airband antenna and found this on a Google
search. Anybody actually own one and can tell me how they perform?

http://www.nevadaradio.co.uk/acatalo...airmaster.html


Troy
Why not try a !good! amateur dual band 2m/70cm antenna, a lot cheaper, less obtrusive, and IMHO a
lot better.
Marco


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Yes! Or just buy a regular discone OR open dipole. That'll work just as
well but cheaper ;-)

"Marco" wrote in
:

Troy
Why not try a !good! amateur dual band 2m/70cm antenna, a lot
cheaper, less obtrusive, and IMHO a lot better.
Marco

Marco wrote:
Why not try a !good! amateur dual band 2m/70cm antenna, a lot
cheaper, less obtrusive, and IMHO a lot better.

This may not really be a good idea.
The aircraft band is a long way from the 2m bands and you will be using the
antenna well outside its designed frequency band. Depending on the precise
construction of the antenna, it may receive no better than a damp piece of
string. My own 2m/70cms co-linear (well sited, outside) actually receives
less than a discone in the loft on airband. No contest on 2m or 70cms
though, the co-linear is far better.

--
Laurie