[TowerTalk] Multiband wire antennas

n4kg@juno.com n4kg@juno.com
Sat, 3 Feb 2001 09:11:56 -0600

Anyone using ANY type of multi-band wire antenna
should model the antenna on EACH band to see
what directions the resulting patterns cover.

The popular ladderline fed 80M dipole has the following
configurations / patterns:

80M	1/2 WL dipole	Broadside pattern 70 degrees wide
40M	2-1/2 WL in phase  Broadside pattern 50 degrees wide
30M	~3/2 WL current fed LW  6 lobes, main lobes 40 deg from wire
20M	2 - 1WL LW in phase, 4 lobes, approx 50 degrees from wire
17M	5/2 WL current fed LW 10 lobes, main lobes 30 deg from wire
15M	2 - 3/2 WL LW in phase, 6 lobes, main lobes 30 deg from wire
12M	7/2 WL current fed LW, 14 lobes, main lobes ~28 deg from wire
10M	2 - 2 WL LW in phase 8 lobes, mail lobes >30 deg from wire

The above lobe orientations are from memory.  
Best to model the wire if you want exact numbers.
BTW, a coax fed 80M dipole (3.6 MHz) can be used
on the WARC bands with <3:1 SWR on 30M and
<2:1 SWR on 17 and 12M.  GREAT antenna but
you will need more than one for 360 degree coverage.

When used as an inverted vee, the nulls fill in and
the gain drops in the main lobes, i.e. it radiates
"equally poorly in all directions".  The smaller
the apex angle, the worse it gets on higher bands.

The OFF  CENTER  Fed wire antennas fed 1/3 way 
from the end looks like 300 ohms at the 1/2 WL frequency 
and all EVEN harmonics, e.g., 80M, 40M, 20M, 10M.
A 130 ft 1/3 off center fed wire will have a broadside
pattern on 80M, 4 lobes on 40M, 8 lobes on 20M,
and 16 lobes on 10M.  The strongest lobes will be 
closest to the wire.  The more lobes, the more narrow
their coverage. 

de Tom  N4KG

On Fri, 2 Feb 2001 Thor Hallen <thorh@worldnet.att.net> writes:
> Bill:
> The "Carolina Windom" is an Off Center Fed dipole rather than a true 
> Windom 
> as both are described in the ARRL Antenna Book. By feeding off 
> center, a 
> reasonably low SWR  in the range of 2 to 4 can be expected on most 
> harmonics of the half wave resonant frequency which in this case is 
> 80 
> meters. An antenna tuner is still required on most bands. You may 
> not care 
> for the radiation pattern on 40 meters as the main lobes are off the 
> ends 
> with a high radiation angle and a null occurs on the sides.
> The G5RV will provide a comparable SWR and has an oval radiation 
> pattern on 
> 40 meters with the broadside being about 6 db stronger than off the 
> ends. 
> The G5RV is also slightly shorter at 102' compared to 130' if that 
> is a 
> consideration. Be aware that the ARRL Antenna Book (18th Edition) 
> incorrectly describes the G5RV matching transmission line as 75 ohms 
> rather 
> than 300 to 450 ohms. Having tried both antennas, the G5RV is my 
> personal 
> preference.
> - Thor Hallen K5AGE
> -----Original Message-----
> From:	Bill Marchand [SMTP:wa1dxa_@snet.net]
> Sent:	Friday, February 02, 2001 10:20 AM
> To:	towertalk@contesting.com
> Subject:	[TowerTalk] Multiband wire antennas
> Does anyone have any experience with a multiband antenna known as 
> the
> "Carolina Windom"?  Trying to decide between basic dipole, G5RV, or 
> the
> Windom as the next antenna here.
> Thanks,
> Bill WA1DXA

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