Hello Phil,
As you say you have asked very many questions. I will try and answer.
> most coastlines are far from straight, and sometimes it becomes
> necessary to site the receive station on a headland or island. This
> puts a land mass in between the receive antenna and part of the sea
> area to be watched. Calculations using REC368 and Millingtons
> method indicate that the receive antenna can be sited up to 10 kM
> from the coastline, and beyond this a considerable directivity gain
> is required from the receive antenna in order to increase the signal
> (which by day comes from one direction) and the noise (which comes
> from all directions.)
A Beverage antenna needs to have poorly conducting ground beneath it
to function properly, the lower the ground conductivity the better the
gain.
For conventional antenna, vertically polarized antennas, the
performance for low angle skywave reception depends on having good
ground conductivity in front of the antenna for 50-or more wavelengths
(the Fresnel zone).
However, for ground wave, so long as the Beverage antenna is over poor
ground, and the wave tilt is well estasblished, the antenna should work
well --- but I do not know what that distance is.
> I am rather concerned however that it would be susceptible to the
> effect of nearby e/m sources such power lines (how would the
> recevers work without power, should they bury the power cable ?
Beverage antennas are less susceptable to man-made noise than
conventional antennas.
> The questions are therefore
>
> 1 What directivity gain can be achieved (as attributable directly to
> the antenna c/n output) ?
See the Tables below. Gain and directive Gains have been calculated
by NEC-2 employing elevated radials (see below) --- these are space
wave gains, but ground wave gains will go in proportion.
> 2 Having tuned in the antenna in the summer when the ground is dry,
> how stable is the directivity with changes in weather, ie during the
> rainy season when the ground conductivity and permittivity suddenly
> change ?
I do not understand your reference to "tuning", since the Beverage is
a very, very broad band antenna, it requires no tuning. However its
gain and directive gain will change if the ground conductivity
changes, significantly.
> 3 Can you suggest any other cost effective solutions for increased
> directivity ?
No, no other antenna will give these sorts of directive gains, and low
noise signal reception. While the power gain is inferior to a rhombic
for example, gain affects both signal and noise. And, since the
antenna is low to ground it is less susceptable to man made noise, and
S/N is generally improved, in fact normally improved significantly.
> As a member of WP8B I ahve been tasked with proparation of draft new
> ITU-R recommendation on prediction of the extent of the A2 sea area,
> plus shore-station design guidelines, but I have not included them
> as they are long documents. Let me know if you would like a copy.
Yes please.
> I am currently running EZNEC . We have recently been sponsored by
> the UK MOD for NEC4, for which I have received the manuals.
If you are licenced for NEC-4, normally one purchases a copy of NEC-4
from Jerry Burke, but you can then purchase the NEC-4 engine from Roy
Lewallen, W7EL. And, EZNEC/4 Version 2.5 (which I use) is user
friendly and has a number of attractive features --- such as
automatically making radials, automatic segmenting, automatic segment
taper option, etc. The automatic segmenting I like, since you can
segment at a frequency 3-10 times higher than the model frequency, for
improved accuracy, and it is easy to change the segment size to see
how this affects the result.
> I do not have time or funds to compile the source code listing I
> have received, and so I am looking for a good package to upgrade to.
> WIN-NEC/GNEC has been suggested, do you have experience of this
> package. I have also been trying to loacte the provider for EAM-NEC
> to no avail
I know nothing about WIN-NEC/GNEC.
> I want to use NEC to create such a structure, and need to put the
> groundwave output into the zero elevation level. (The entire
> structure is normalised to EMRP, a reference common to REC535 for
> skywave and REC368 for groundwave). Can you advise how to do this
> with NEC4, and whether you think I could achive this with GNEC,
> assuming buried radials.
EZNEC/4 calculates ground wave and spacewave separately. The ground
wave can be calculated for any distance and any height above ground.
The Beverages we have built employ 25 fifty foot radials buried, at
each end; but for a Beverage, which is a lossy antenna, you can do
just as well (from the point of modelling) using NEC-2 by placing the
radials a few wire diameters (say 5mm) above the ground.
120 resonant radials 5 mm off the ground (resonant means the are very
much shorter than a quarter wavelength) will according to NEC-4 yield
the same field strength (with a dB or so) as 120 quarter wavelength
radials buried.
> One further point, I would like to obtain copies of the papers you
> refer to below and in other correspondence . I would especially
> like to get a copy of "Beverage Antennas for Amateur Communication",
> J.S. Belrose, J. Litva, G.E. Moss and E.E. Stevens, QST, pp. 22-27,
> January 1983. and copies of your papers on elevated ground radials
> but I do not know how to obtain them in the UK, could you please
> advise.
> I realise I have asked you quite a few questions, but I really
> would appreciate your advice. There are only a few people I know to
> ask. I started this business in the BBC, going almost directly from
> school to the antenna farm at Skelton, I am afraid many of my
> ex-seniors from BBC days are no longer crunching the keyboards.
Send me your address and I will mail copies.
Finally, if you do not want to construct your own Beverage, Petrie
Telecommunications, Len Petrie, 68 Tripp Crescent, Nepean ON K2J 1C8
[TEL 613-825-1505; FAX 613-825-2249] could supply you with one. He
provides all the hardware (matching transforms, etc.). He can also
supply a rosette array, 24 Beverage elements looking in all
directions. He has installed a number of Beverage antennas, and
Beverage rosette arrays for the Canadian Military --- all for
satisfied customers.
Regards, 73,
Jack
Table 1
Radiation characteristics for a 450 Beverage, 8 feet high, over average ground.
Frequency Power Directivity Launch
MHz Gain, dBi Gain (dB) Angle
(Azimuthal Beam Width)
28 9 (24) 21.6 13
24 7.9 (26) 21.2 13
18 6.1 (30) 19.6 15
12 3.3 (36) 17.8 18
8 0.4 (44) 16.1 21
4 -3.7 (60) 13.1 29
2 -8 (94) 9.3 42
Table 2
Radiation characteristics for a 600 Beverage, 8 feet high, over average ground.
Frequency Power Directivity Launch
MHz Gain, dBi Gain (dB) Angle
(Azimuthal Beam Width)
28 10.2 (20) 23.6 11
24 9.1 (22) 22.3 12
18 7.2 (26) 21.2 13
12 4.3 (30) 19.6 16
8 1.5 (36) 17.8 19
4 -2.6 (50) 14.7 25
2 -7.2 (70) 11.5 32
Table 3
Radiation characteristics for a 750 Beverage, 8 feet high, over average ground.
Frequency Power Directivity Launch
MHz Gain (dBi) Gain (dB) Angle
(Azimuthal Beam Width)
28 11 (18) 24 10
24 9.8 (18) 24 11
18 7.9 (22) 22 12
12 5 (27) 20.4 14
8 2.2 (33) 18.5 16.5
4 -1.9 (44) 15.7 21.5
2 -6.4 (64) 12.3 29
_____________________________________________
John S. (Jack) Belrose, PhD Cantab, VE2CV
Senior Radioscientist
Radio Sciences Branch
3701 Carling Avenue
PO Box 11490 Stn. H
OTTAWA ON K2H 8S2
CANADA
TEL 613-998-2308
FAX 613-998-4077
e-mail <john.belrose_at_crc.ca>
_____________________________________________
Received on Thu Apr 30 1998 - 06:26:42 EDT
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