[Antennas] Vertical

2002年9月28日 13:07:00 -0700

Ed
Not a straight forward Yes/No type question. Certainly on the roof would be
better than on the ground with buried radials. Other factors to consider
might involve what Take Off (TO) angle you want to cover that your beam
doesn't. Also, probably need to know your actual ground situation (poor,
excellent, etc.) in order to model it adequately. The following are notes
from data generated by MINNEC 3 for a 20 meter vertical dipole over 'real'
ground. I used a vertical dipole as it is easiest to model. A 1/4 wave
vertical with radials will probably be close but not sure how close. Also,
this was what I used to choose between a vertical and an inverted vee. (If
you use an inverted vee with 120 deg angle, that is often as good, if not
better than a vertical dipole at the same height for heights above 1/3 WL or
so).
Note that the primary TO is lowest at the 1 WL height. But, it varies
higher and lower at various heights (e.g. 14 deg at 1/4 WL to 44 deg at 3/8
WL). Also, the secondary lobe is a factor as that varies all over the place
also.
If it were me, I'd probably mount it on the roof (but never directly on the
ground with buried radials as that is why verticals are said to radiate
equally poorly in all directions) as I'm guessing that will get it up, or
above 3/8 WL. From this data, looks like 3/8 WL height up to 1 WL would
give you pretty good combined coverage using 1st and 2nd lobes. Above 1 WL,
I suspect a single lobe of low angle is primary so it may not give you the
'omni directional' azimuth coverage I suspect you want but it probably would
work real well for low angle 'long hauls'. Haven't modeled the height of
your tower but that would need to be done before making absolute
conclusions.
Commercial verticals like GAP and C/C are not easy to model due to all the
'gizmos' they use to achieve resonance. Suspect the issues of multiple
lobes, ground quality, etc are important for them as well. The simpler
approach used by Hy-Gain in their 'short radial' AV-620 and AV-640 multiband
verticals might be fun to try next. Not sure when I'll get to it.
20 Meter Vertical Dipole
			Primary	Secondary
HT of bottom	Lobe		Lobe
above ground	TO	Gain	TO	Gain
(WL)			Angle	(DBi)	Angle	(DBI)	Comments
1.0000		9	3.12	21	2.81	Tertiary lobe at 48 deg w 0.39 Dbi
0.8750		25	2.98	9	2.73	tertiary lobe at 54 deg w -1.24 Dbi
0.7500		28	3.01	10	2.37	tertiary lobe at 61 deg & -4.28 Dbi starting to
emerge
0.6250		32	2.78	11	1.86
0.5000		37	2.21	11	1.31	Both lobes are useful
0.3750		44	1.18	12	1.00	High lobe has taken over but 1 Dbi gain still at 12
deg
0.2500		14	0.96	50	-1.04	Noticeable high lobe
0.1250		16	0.80	56	-6.73	Small but noticeable high lobe emerging
0.0625		18	0.55			No high lobes
0.0001		19	0.20			Resonance shifted down 200 KHz
73 de Jim WA6PX
[email protected]
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of [email protected]
Sent: Saturday, September 28, 2002 12:26 PM
To: [email protected]
Cc: [email protected]
Subject: Re: [Antennas] Vertical
Now you've piqued my interest...My intent was to always to have a vertical,
in addition to yagi antennas. This allows one to hear signals arriving at
different angles and gives omnidirectional coverage. Hence, I was going to
put one on the roof with radials. Would you suggest putting a no
radial-type
on my tower at 85' instead??? I was thinking of the C/C R6...
Thanks,
Ed NI6S
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