Thanks again John,
As for switching.... the rotary dipole I have, a F12 Magnum, has 3
relay/coils and it covered from 3.5 - 4.0 at under 1.6:1 ... its relatively
easily done so I'm not sure that is a concern.
And one can get 'cute' and design it to be instantly reversible. I've
modeled this. Granted it is 130' in the air so there is a substantial con
there....
again, not ignoring the concern as much as thinking about ways to eliminate
or at least reduce the concern through better design.
The reason why I'm going down this route is simply because of the poor
ground conditions there. Also the vertical would have to be installed
looking into a ~5 degree surface elevation rise
over about 135'. I haven't a clue how to model that so I'm a bit concerned
it will have a marked (negative) effect on the 4 sq's performance. And it
happens to be in the direction of: EU and AF!
Gary
-----Original Message-----
From: john@kk9a.com
Sent: Sunday, March 15, 2015 12:45 PM
To: 'StellarCAT' ; towertalk@contesting.com
Subject: RE: [TowerTalk] modeling compare: 80M, 2EL vs 4SQ
NEC-2 will not accurately model ground radials. I am certainly not a
vertical expert but I am thinking that the far field is what effects the
radiation pattern and unless your redials are wavelengths long they will
have little effect other than to minimize ground losses. For ease of
maintenance and the ability to easily switch from CW to SSB band segments, I
would pick the 4 square over a Yagi. From a gain standpoint they are
probably pretty close in an average installation.
John KK9A
-----Original Message-----
From: StellarCAT [mailto:rxdesign@ssvecnet.com]
Sent: Sunday, March 15, 2015 1:12 PM
To: john@kk9a.com; towertalk@contesting.com
Subject: Re: [TowerTalk] modeling compare: 80M, 2EL vs 4SQ
Hi John,
I'm not sure what you're suggesting here.... I can go from the model with no
radials and see a particular max gain and shape of the
pattern... then add 17 radials each, even short ones at 0.15 wl, and the max
gain is considerably higher and the pattern is much
lower at very low angles (i.e. gain at low angles) with the front lobe now
pushed downward towards 0 degrees. What am I
missing in your comment?
I did get a direct comment from W4TV suggesting I simply change the height
of the radials so they're in different planes - great idea,
a 'duh' moment. So I'll give that a try. With that I can do 32 radials that
are nearly 1/4 wl long. I'll see what that will do.
Finally I had the suggestion to stick with the 4 sq simply because of
maintenance and cost... which I can appreciate completely...
but one CAN design and build an element and boom that will survive say 90
Mph winds with 1/4" ice (the area we'll be in is rated 70 Mph
and has occasional icing) and the tower is already planned... if indeed the
4 sq suffers considerably by the ground quality then that
might be a way forward. I DO love 75/80!
.... just finished adding 32 1/4 wl radials (per W4TV's suggestion having
them at 0.1, 0.2, 0.3, 0.4' on each element)...
using high accuracy gnd always and...
Antennas:
-4 sq with 32 67' long radials
-rotary dipole at 130'
-2 el 36' boom yagi at 130'
2mS conductivity:
@ 5 degrees elevation:
The 4 sq is better by ~ 3 db compared to the dipole,
the 4 sq is worse than the yagi by about 2 DB
@ 10 degrees:
the 4 sq is 1 db better than the dipole
and the 4sq is almost 4db worse than the yagi
The 4Sq peaks at 5.68 db at 26 degrees
The dipole peaks at 7.96db at 30 degrees
The 2el peaks at 11.48 db at 25 degrees.
Note a large part of the US has 2mS as the ground conductivity!
Comments on my (hopefully soon to be) situation (with 2mS):
-the 2 el always equals or beats the 4 sq - often by a significant amount!
-except for very low angles the rotary dipole does quite nicely against the
4Sq re gain ...
however of course the dipole has no FB which on 80 meters is probably more
to much more important than gain...
(especially from South Carolina with most of the US behind the antenna a
good share of the time)
-------------------------------------------
8mS conductivity (previous location in southern Arizona):
@ 5 degrees elevation:
the 4 sq is better by 4.5 db compared to the 130' dipole,
the 4 sq is about equal to the yagi
@ 10 degrees:
the 4 sq is 3 db better than the dipole
and the 4 sq is just under 2db worse than the yagi
The 4Sq peaks at 6.68 db at 22 degrees
The dipole peaks at 7.96db at 30 degrees
The 2el peaks at 11.48 db at 25 degrees.
If anyone wants this model please drop me an email.
Gary
K9RX
-----Original Message-----
From: john@kk9a.com
Sent: Saturday, March 14, 2015 9:59 PM
To: towertalk@contesting.com
Cc: rxdesign@ssvecnet.com
Subject: re: [TowerTalk] modeling compare: 80M, 2EL vs 4SQ
I do not believe that the radials will have an effect on the radiation
pattern.
John KK9A - W4AAA
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