"Dan Morisseau" wrote in message
...
T-bone wrote:

I just don't think that discones should be dismissed as pure junk.
Within their limits, I've found them to be fine general all around signal
recievers, which is what their purpose is.

Agreed! You are absolutely right. George has been shilling Scantennas for
Antenna Warehouse for several years now. He belittles whatever else anyone
my recommend and refuses to acknowledge that another product may suffice
for another's purposes. His shamelessly partisan promotion gets old after
awhile.

A discone is going to exhibit no gain, in fact probably less than unity
gain, when compared to an isotropic, but you can essentially call a discone
a 0 dB gain antenna across its entire bandwidth of operation. Using an
oversimplification, the lower frequency of the discone will be largely
determined by cone and disc element lengths (about 0.25 and 0.17
respectively), the upper frequency by the gap between the two. Although a
discone will probably only exhibit an ideal response across about a 3 to 1
range (well short of this gap limitation). A dipole will exhibit a slight
gain over the same source (isotropic), about 2.7 dB in the real world,
across its bandwidth. However, the dipole will be much more narrow banded.
The dipole has a single resonant frequency, determined mostly by physical
size. It is easy to use transmit bandwidth to define 'peak' operation.
Transmit bandwidth is defined as the band between the two frequencies at
which the SWR on the feedline has risen to stated values, it being assumed
the SWR at the band center has previously been adjusted by some means to be
1:1. However, receive bandwidth can also be defined. Receiving bandwidth
is defined as the band between the two frequencies at which receiver input
power has fallen to 1/2 the level at the band center. It is described as the
3dB bandwidth. For a Zo-matched receiver, 3dB bandwidth is 2*Fc/Q where Fc
is the center frequency and Q is the intrinsic Q of the antenna. Remember
this Q and look at where it is in the formula. For receive antenna purposes
a lower Q will mean a broader bandwidth.

The Scantenna is a modified multiple dipole antenna, on the quoted website
it calls it a '15 element clustered dipole design'. The elements that splay
out from the main element are there to broaden the bandwidth. The short
elements on the mounting boom are to cover the higher frequencies. Without
having tried the antenna myself, but having more than a little bit of
professional experience with RF, I can make a pretty good stab at what I
would expect the antenna to do in use. The longest length is about 101
inches. This is going to put the lowest usable frequency around 50 MHz.
Guestimating the length of the other elements from this 101 number it looks
like they have selected lengths that fall near certain bands, probably the
'major' scanner bands. So that the antenna will probably function quite
well in those frequency areas. If you stay in those bands you will probably
get better performance with the scantenna than you will with the discone.
However, outside those narrow bands the discone will probably perform
better.

One thing to note. At the higher frequencies the Scantenna seems to use
short boom mounted dipoles. These WILL display a directionality based on
the relationship of the received signal directions to the main set of
elements. In other words, it will look 'down' the boom better than to the
side. At those higher bands the Scantenna will probably display a better
performance ONLY when the transmitting station is along this direction.
Other than that the discone will probably appear to perform better on
average.

So, depending on your primary scan activities, the discone will probably be
the less limited choice. But, if the Scantenna fits your specific
application it may exhibit a slight performance edge, within its band
limitations.

All just a guess on my part, but defendable. For most things I would opt
for a well designed and built discone myself.

C