discone vs ground plane
str...@hotmail.com
the best scanner antenna to have? Or would a ground plane tuned to the
freqency you are listening to be better?
Tad Danley
It depends - a ground plane may work better than a discone for the
frequency range for which the ground plane is tuned, however it would
probably be hard to notice the difference. A discone will definitely
work better than a ground plane for frequency ranges far from the
intended range of the ground plane. If you are looking for one antenna
to monitor several different bands, a discone is a nice way to go.
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Tad, K3TD
Colic
<str...@hotmail.com> wrote in message
news:1105286806.0...@c13g2000cwb.googlegroups.com...
>I keep reading discones cover a very wide frequency. Are these truly
> the best scanner antenna to have? Or would a ground plane tuned to the
> freqency you are listening to be better?
>
If you have one specific frequency, or a narrow frequency band of less than
about 10%, then a properly designed and built ground plane antenna will have
significantly more gain. It would be easy to get 5 to 8 more dB of signal
from the ground plane over the discone. It is possible to get 10 to 12 dB
or more from the ground plane (over the discone only, I am not saying 10-12
dB gain over an isotropic), but this starts to narrow up the bandwidth below
the above mentioned 10%.
What is 5 to 12 dB more signal? Every 3 dB is double the signal strength.
A gain of 12 dB would be a signal about 17 times the signal of the discone.
What does 10% of bandwidth mean? If you design a ground plane for a center
frequency of about 150 MHz it will work across about a 10% bandwidth (this
is a rule of thumb, but not hard and fast). 10% means the antenna will have
a 15 MHz band width of optimum performance. Or about 142 to 157 MHz
(rounded off). The antenna will work outside this range, naturally, but the
gain will fall off rapidly.
For broad band applications it is very hard to beat the discone antenna.
This is why the discone is so popular with the military and countermeasures
community. The discone is not best at any one thing, but it takes the place
of a multitude of other antennas and does it reasonably well.
C
Mike
numbers come from? If you look at the gains and plots from any
commercial/military Discone you will see it is about on par with a 1/4
wave groundplane across most of the Discone bandwidth. I don’t mean
inflated scanner Discone specs, look at commercial companies that
reference to isotropic or 1/2 wave dipole for measurements. At the upper
end of the Discone’s range the pattern can get a bit squirrelly, but
then a ground plane with only 3 or 4 radials does not put all of it’s
energy at the horizon either, the mail lobe is at least several deg
higher than the horizon. A “scanner” type Discone will perform within 1
or 2dB of a 1/4 wave groundplane on the VHF and UHF bands, which is the
lower end of its useable range. What does this really mean? You will
probably not notice any difference between a good quality Discone and a
ground plane cut to frequency on the VHF or UHF bands. 800 MHz would
benefit from a gain type antenna if your in a fringe area.
Mike
Brian
wrote:
GET A DRESSLER ACTIVE ANTENNA
IT WILL OUT PREFORM BOTH OF THE OTHER ANTENNAS 25- 1200MHZ
Colic
"Mike" <km...@REMOVETHIS.pacbell.net> wrote in message
news:NjjEd.9788$5R....@newssvr21.news.prodigy.com...
>A ground plane has 5 to 8dB more gain than a Discone? Where do these
>numbers come from? If you look at the gains and plots from any
>commercial/military Discone you will see it is about on par with a 1/4 wave
>groundplane across most of the Discone bandwidth. I don’t mean inflated
>scanner Discone specs, look at commercial companies that reference to
>isotropic or 1/2 wave dipole for measurements. At the upper end of the
>Discone’s range the pattern can get a bit squirrelly, but then a ground
>plane with only 3 or 4 radials does not put all of it’s energy at the
>horizon either, the mail lobe is at least several deg higher than the
>horizon. A “scanner” type Discone will perform within 1 or 2dB of a 1/4
>wave groundplane on the VHF and UHF bands, which is the lower end of its
>useable range. What does this really mean? You will probably not notice any
>difference between a good quality Discone and a ground plane cut to
>frequency on the VHF or UHF bands. 800 MHz would benefit from a gain type
>antenna if your in a fringe area.
> Mike
Most discones do not exhibit gains as high as a 1/4 wive ground plane across
a wide bandwith. They (the discone) may approach these numbers at their
best points. However the real issue here is that all ground plane antennas
are not 1/4 wave. When I quoted the 5 to 8 dB better gain possible from a
ground plane I was talking about ground planes with more gain than a 1/4
wave. A 5/8 wave would have several dB more gain. Compare a 5/8 wave
ground plane to the 'average' scanner store discone (and they are in the
same price bracket) and it is easy to get around 5 dB. Or, a colinear could
get up into some real gain compared to the discone. So, while I agree with
you that a well made discone may be fairly close to a 1/4 wave ground plane,
it is far easier to make a high gain ground plane than it is to find a well
made discone. Most three wire coned scanner discones would be lucky to get
close to an isotropic, let alone the almost 3 dB more you would get from a
half wave dipole.
The last time I looked at a well made military discone (say an AT-197/GR)
the price was several times the price of a killer colinear vertical. Of
course, if you can get one surplus it can be cheap, I have three 197's
myself.
The contention of my post was that dollar for dollar, if you are interested
in one specific frequency or narrow band, you can get more gain with a
different antenna rather than the discone. However, a well built discone
will generally be my preferred choice for anything like a scanner or
multibanded receiver if it is physically possible. A discone on 160 M may
be possible, but I can think of a couple other choices I would try first.
C
Mike
for the price. I borrowed two of the active VHF/UHF Dresslers from the
local rep (forget the model but went to 2GHz and was not the high IP3
version) and tested them on a antenna range against a Radio Shack
Discone. The source antenna was a commercial 50MHz to 1GHz log periodic.
I don’t have the results handy but above the mid VHF range the Dressler
did a little better than the Discone but not by much, the best
performance was about 5 or 6dB at 1ghz if I remember correctly, which
was my upper test limit at the time. Oddly, the Discone worked about the
same on VHF high band and much better in the VHF air band. What was more
surprising was the Discone was better from 50MHz to 100MHz than the
Dressler even though the Discone was below it’s natural cut off freq of
around 100MHz. I thought something was wrong with the Dressler but both
units gave the same results and the Dressler gain control was all the
way up in both cases. The rep confirmed they were both working properly
when returned also. Without opening the Dressler, we could only conclude
the “antenna” element inside was a poor design and the internal pre-amp
can only do so much with what its fed. Much better performance could be
had starting with a Discone and feeding it with a Dressler or similar
pre-amp, which the local rep uses himself. If you hear of a good report
from a Dressler owner, it’s probably because they have to justify the
high price they paid for the thing.
The reason I went to all the trouble of setting this test up was to find
a replacement for an active antenna I had that died after a lightning
strike. It had a very complicated trapped “fat dipole” that presented
its internal pre amp with a good match from 50MHz to around 2GHz and
outperformed anything I have ever use for monitoring purposes. It
performed as good as many of the large high gain commercial antennas I
have and also had enough gain to feed several receivers. Never
encountered any intermod problems in the RF dense LA CA area either, it
was the best of everything. Unfortunately, it was a prototype and I
cannot locate the designer who mad a small test production run of these
things.
Mike
Mike
The antenna did not have a brand name and I have not seen one advertised
anywhere. I cannot locate the designer or the company that manufactured
one of his other designs. Very frustrating for me.....I tried replacing
the two amplifier chips in the antenna but got lousy performance with
lots of overload, I cannot identify the original parts. I now use
several military and commercial Discones and large commercial VHF/UHF
dipole arrays for monitoring and can't recommend a specific antenna for
you without hearing about your needs, freq range, distance to cover,
proximity to large transmitters, etc. I am not very informed about other
active VHF/UHF antennas except the Dressler but there are several
others. If you need to monitor a broad range of frequencies you could
start with a Discone tailored for your needed freq range and place a
good pre amp right at the antenna to get the best noise figure and make
up for cable losses. The Dressler pre amp is supposed to be a very wide
band high level unit that should not be as susceptible to overload as
other brands I have seen.
Mike
Stephan Walther Larsen wrote:
> On Mon, 10 Jan 2005 02:09:47 GMT, Mike <km...@REMOVETHIS.pacbell.net>
> wrote:
>
>
>>The reason I went to all the trouble of setting this test up was to find
>>a replacement for an active antenna I had that died after a lightning
>>strike. It had a very complicated trapped “fat dipole” that presented
>>its internal pre amp with a good match from 50MHz to around 2GHz and
>>outperformed anything I have ever use for monitoring purposes. It
>>performed as good as many of the large high gain commercial antennas
>
>
>
> Mike
>
> Id like to know what that antenna was that died on you..im looking for
> the best ( money is not particular a limit ) broadbanded antenna for
> my AOR5000+3.
>
> I had a dressler 2000 but it died on me and didnt perform all that it
> was hyped to..not a big loss to me. However id appreciate an advice
> on a good commcial brand antenna for my Aor.
>
> Stephan in Denmark
Mike
The antenna did not have a brand name and I have not seen one advertised
anywhere. I cannot locate the designer or the company that manufactured
one of his other designs. Very frustrating for me.....I tried replacing
the two amplifier chips in the antenna but got lousy performance with
lots of overload, I cannot identify the original parts. I now use
several military and commercial Discones and large commercial VHF/UHF
proximity to large transmitters, etc. I am not very informed about other
Discone tailored for your needed freq range and place a good pre amp
right at the antenna to get the best noise figure and make up for cable
losses. The Dressler pre amp is supposed to be a very wide band high
I have seen.
Mike
Stephan Walther Larsen wrote:
> On Mon, 10 Jan 2005 02:09:47 GMT, Mike <km...@REMOVETHIS.pacbell.net>
> wrote:
>
>
>>The reason I went to all the trouble of setting this test up was to find
>>a replacement for an active antenna I had that died after a lightning
>>strike. It had a very complicated trapped “fat dipole” that presented
>>its internal pre amp with a good match from 50MHz to around 2GHz and
>>outperformed anything I have ever use for monitoring purposes. It
>>performed as good as many of the large high gain commercial antennas
>
>
>