Hi Dick
"I never noticed any difference in receiving performance"
That's exactly what we should expect using a resonant dipole, it interact
with any other antenna because the fiscal length is resonant, does matter if
the feed impedance, if it is only a straight wire resonant it is like a
director or director. Distance also is something hard to manage on 160m.
120ft is only 1/4 or .25 wave , heavely interact with other resonant
elements.
A low dipole is like an inverted V, used to be called unidirectional, a high
dipole is different because the vertical field change intensity far from the
ground, however the feed line is hardtop choke and remove the vertical
common mode noise. Ladder line has huge advantage here , but not worth the
effort .
The low dipole and inverted V is unidirectional only if you disregard the
polarization, using EZENEC it is easy to demonstrate that, check Plot Type:
3D plot and select Desc Options Ver.Horiz.Total. When you plot the 2D
Azimuth Slice or Elev Slice, the vertical field is the red line and the
horizontal a green line.
The inverted V or low dipole is horizontal only at broadside with a 8 patter
and some RDF, along the wire the Inverted V and low dipole is vertical
polarized. Bothe fields are high angle, it means low gain at low angles.
Both antennas work like a very short beverage along the wire and does not
perform at all. Broadside there is a huge deep null on vertical signals, as
a result the manmade noise is also attenuated that direction, the horizontal
signal sky wave 20 to 40 degree has less attenuation, that situation there
is an increase in the signal to noise ratio. The lobe is very wide and the
SNR is better at the center and at 45 degree each side the vertical field is
the same as the horizontal field, that's why these antennas are
unidirectional, with the two fields the same there is no improvement on SNR
after 45 degree from the center
The situation where these antennas outperform vertical arrays is because
they receive horizontal sky wave signals or high angles vertical or
horizontal signals.
Any receiver antenna without directivity is works like the attenuator in
your radio, just reduce the overall gain decrease the Noise figure of the RX
system but increase the IP3 reducing intermodulation. Almost the same thing
as reduce the RF gain and increase the audio gain does.
Receiver antennas to perform must have good RDF, and keep no other resonant
anything around, only one resonant wire will be part of the RX system and
change the patter, is the wire works like a director or reflector it would
increase the RDF , the odds are not that and most of the cases the
interaction makes the RX antenna patter useless.
This long answer is to validate your observation, resonant dipoles does not
provide any difference in receiver performance than your vertical or TX
antenna.
73's
JC
N4IS
-----Original Message-----
From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Richard
Karlquist
Sent: Saturday, December 20, 2014 4:49 PM
To: topband@contesting.com
Subject: Re: Topband: Non-resonant receive antennas
On 2014-12-20 13:06, Richard Jaeger wrote:
> I guess I should try a low dipole and see what happens.
>
> Dick, K4IQJ ..
>
When talking about a low dipole, the question comes up as to why it must be
low to work. Actually we don't know that it must be low to work. Very few
of us are in a position to put up a "high" dipole, so the question is
basically moot. However, in an attempt to gauge the influence of height, I
A/B'ed two full size dipoles at
30 and 60 foot heights over a period of 6 months. The one not in use was
floating to avoid interaction with the active one.
I never noticed any difference in receiving performance.
What seems to happen is that the signals are a few dB higher on the 60 foot
wire, but the noise is commensurately higher. 30 feet was chosen for the
minimum so that the wires didn't look like beverages (and because I have a
bunch of 30 foot lengths of pipe).
Rick N6RK
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
_________________
Topband Reflector Archives - http://www.contesting.com/_topband
|