Just to set the record straight.
dBi = dB(isotropic) – the forward gain of an antenna
<https://en.wikipedia.org/wiki/Antenna_gain> compared with the
hypothetical isotropic antenna
<https://en.wikipedia.org/wiki/Isotropic_antenna>, which uniformly
distributes energy in all directions. Linear polarization
<https://en.wikipedia.org/wiki/Linear_polarization> of the EM field is
assumed unless noted otherwise.
dBd = dB(dipole) – the forward gain of an antenna
<https://en.wikipedia.org/wiki/Antenna_(electronics)> compared with a
half-wave dipole antenna <https://en.wikipedia.org/wiki/Dipole_antenna>.
0 dBd = 2.15 dBi
dBiC = dB(isotropic circular) – the forward gain of an antenna compared
to a circularly polarized
<https://en.wikipedia.org/wiki/Circular_polarization> isotropic antenna.
There is no fixed conversion rule between dBiC and dBi, as it depends on
the receiving antenna and the field polarization.
dBq = dB(quarterwave) – the forward gain of an antenna compared to a
quarter wavelength whip. Rarely used, except in some marketing material.
0 dBq = −0.85 dBi
dBsm = dB(m²) – decibel relative to one square meter: measure of the
antenna effective area
<https://en.wikipedia.org/wiki/Antenna_effective_area>.]
<https://en.wikipedia.org/wiki/Decibel#cite_note-60>
dBm−1 =dB(m−1) – decibel relative to reciprocal of meter: measure of the
antenna factor <https://en.wikipedia.org/wiki/Antenna_factor>.
73
Bob, K4TAX
On 3/13/2020 6:08 PM, David Gilbert wrote:
Lyn,
A dipole over ground has considerably more than 2.14 dbi maximum gain,
and since you said you had a tree in the middle I assumed (probably
incorrectly) that it was enough in the middle to allow a 40m dipole to
fit crossways your lot to other trees. If that isn't the case, OK.
You didn't say whether your model that gave you 4.7 dbi for the EDZ
was a free space figure (and I'm too lazy to model it myself now to
check), but if so yes ... there would be at least a 2.5 db benefit to
the EDZ. I've done my own tests to demonstrate the clear advantage
that even 2 db can provide (see
http://www.ab7e.com/weak_signal/mdd.html), but I still wouldn't call
that "far outperforming".
And who said anything about putting up a rotating yagi?? Your EDZ is
not rotatable so why eliminate a wire yagi from consideration because
it isn't. As I said, you do have to settle for unidirectionality but
your original comment was that other wire options would beat the yagi
for gain ... they don't.
I've read your reply three times now and still don't understand what
20KW into a ten curtain array has anything to do with this discussion.
Dave,
AB7E
On 3/13/2020 12:49 PM, Lyn Norstad wrote:
Dave -
I actually /do/ consider 4.7 dbi as "far outperforming" 2.14 dbi
(ordinary dipole).
And since cost is an issue for some of us (along with HOA
restrictions), I rejected the idea of getting a couple extra dbi at
the cost of many thousands of dollars. And adding a N-S 40m dipole
fed at the same point would have required either traversing my
neighbor’s yard, or erecting a 2 towers … neither of which is feasible.
And forget the logistics of erecting a 2 element beam for 80 meters
(see OptiBeam OB2-80+ with 74 foot elements on a 36 foot boom), tower
and rotor for that monster.
We have a commercial (HST) shortwave station a few miles away that
runs a 20kw transmitter on various 7 - 10 MHz frequencies into an 18
dbi gain "curtain" antenna aimed over the pole to Europe. Their beam
width is 38º. Ten curtains could be hung using relatively
inexpensive towers or masts spaced at 36º in a circle. The 20kw
input results in an ERP of 808 KW, according to their FCC license, at
an extremely low angle of radiation, and very low maintenance.
That would actually be my first choice.
73
Lyn, W0LEN
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of David Gilbert
Sent: Friday, March 13, 2020 1:39 PM
To: [email protected]
Subject: Re: [Elecraft] Off-Topic: Your advice/suggestion about antenna
That is certainly a perfectly viable antenna and probably a fine choice
for your needs ... but it does not "far outperform" either a dipole or
especially a 2 element yagi at the same height. (although the yagi would
of course be unidirectional). 4.7 dbi is dipole territory. You could
have gotten pretty much the same result with an E-W 80m dipole and a N-S
40m dipole fed at the same point (orthogonal fan dipole). And assuming
you used capacitors for the EDZ, dipoles are easier to build.
73,
Dave AB7E
On 3/13/2020 11:19 AM, Lyn Norstad wrote:
> Duane -
>
>
>
> I am of the mind that the antenna is the most crucial part of any
station,
> and probably the most often maligned. I have made a number of
presentations
> to ham groups on the design and construction process involved in
getting
> the most bang for the buck, depending on your wants and needs
(everybody's
> are different).
>
>
>
> In my own situation (2 acre semi-rural lot approx.150 feet x 600 feet
> running E-W feet, and active HOA) the goal was to have a single
antenna that
> would provide the best primary signal on 80 meters in a North-South
> direction, while providing the best possible signal on 40 meters in an
> East-West direction, consistent with the 80 meter performance and
without
> unduly provoking the HOA (or my XYL).
>
>
>
> I decided on an Extended Double Zepp, cut for 3.5 MHz. That
resulted in a
> length of 360 feet, which worked nicely since I have 400 feet clear
from the
> house (West end) to a perfect tree for the far East end. And
another tree
> in the center for support of both the antenna and the feedline.
>
>
>
> I am feeding it with a 160 foot length of 600 ohm "true ladder
line." I can
> go into more detail if this sounds like something that would work.
Modeling
> this antenna with EZ NEC shows a maximum theoretical gain of 4.7
dbi in both
> North and South directions. With the ladder line, a dual hybrid
balun and
> short length of coax into the shack, my KAT500 tunes it very nicely
on all
> bands 160 m thru 6m.
>
>
>
> I don't have your call so can't see where you are, but would be
happy to
> make other suggestions based on the coverage you seek.
>
>
>
> 73
>
> Lyn, W0LEN
>
>
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