Here we go, roving again during the CQWW VHF contest:
First day FN10, 1800-2100; FN00 2130-0030, FN09 0045--0400
Second day FM08 1030-1430, FM18 1445-1730, FM19 1800-2100
all times approximate and are in UTC. We plan to have
6/2/1.25/.7/.23M with good antennas, 1.25 may be FM only, but
will be either polarization as needed. Work us on FM, too, during
the IARU contest--we're hoping for good activity--please call us!
Primary frequency 144.178, FM 146.55/446.00
73 Brian/Rob GO PVRC>>>
>From CT1BOH@tpone.telepac.pt (JOSE C. C. NUNES) Wed Jul 5 19:47:21 1995
From: CT1BOH@tpone.telepac.pt (JOSE C. C. NUNES) (JOSE C. C. NUNES)
Subject: FW: Re: RUFZ
Message-ID: <Chameleon.950705114931.CT1BOH@>
Hi all
thanks to the gracious help of John K2MM everybody can get RUFZ at the
following FTP address as soon as K2MM Puts the program there.
Jose
ct1boh@telepac.pt
>Hi, Jose.
>
>> I got RUFZ ce contest trainner
>> Wonder if I can FTP it to your Disk so that anyone can get it?
>
>Sure.
>
>I've made a directory for you on my FTP server. The server is
>maspar.maspar.com (192.84.231.1), and the directory is /pub/k2mm/rufz.
>
>
(...)
>73. --John/K2MM
>
>From barry@w2up.wells.com (Barry Kutner) Wed Jul 5 13:04:47 1995
From: barry@w2up.wells.com (Barry Kutner) (Barry Kutner)
Subject: Performance of Cushcraft 40-2CD above a tribander
Message-ID: <oaJR8c1w165w@w2up.wells.com>
In follow-up to Frank's (LPL) query:
I have a 402-CD about 9 ft above a TH7. The only band I have any concern
about interatction is 10 meters (yes, 10 meters). The SWR hovers in the
1.5-2.0:1 range from 28.0-28.7 and I can't seem to get it lower.
Performance was poor on 10 until I added a second TH7 at 40 ft (upper at
76 ft). I'm not sure if the performance problem was related to
interaction or just the "wrong" height. Plays very well as a stack. No
problems whatsoever on 15 or 20.
--
Barry N. Kutner, W2UP Internet: barry@w2up.wells.com
Newtown, PA Packet Radio: W2UP @ WB3JOE.#EPA.PA.USA.NA
Packet Cluster: W2UP >WB2R (FRC)
.......................................................................
>From Swanson, Glenn, KB1GW" <gswanson@arrl.org Wed Jul 5 14:26:00 1995
From: Swanson, Glenn, KB1GW" <gswanson@arrl.org (Swanson, Glenn, KB1GW)
Subject: wn4kkn needed permission
Message-ID: <2FFA92CC@arrl.org>
The ARRL land-line BBS (HIRAM) would be a good place for the program.
Uploads (and downloads)-> (203) 594-0306.
73, --Glenn, KB1GW
----------
>From: Trey Garlough
>To: CT1BOH
>Cc: cq-contest
>Subject: Re: wn4kkn needed permission
>
>---------------------------------------------------------------------------
---
>> Mario 5b4wn send me encode file
>> Is it OK to send rufz as messages to reflector so that evrybody can
undecode
>> them and enjoy the program?
>
>Ask someone to serve the item via a service such as Anonymous FTP or
>an email-based file server so people can download it on demand. Then
>you or he/she can post a message announcing where it can be found.
>This will work better than a one-time broadcast of the program,
>because it will continue to be available long after the announcement
>has been sent. In addition, keeping binaries out of CQ-Contest is a
>good thing since it is intended to be a discussion group.
>
>--Trey, WN4KKN/6
>
>From Swanson, Glenn, KB1GW" <gswanson@arrl.org Wed Jul 5 14:36:00 1995
From: Swanson, Glenn, KB1GW" <gswanson@arrl.org (Swanson, Glenn, KB1GW)
Subject: Feeding antennas...
Message-ID: <2FFA9547@arrl.org>
Greetings,
Recently, Chas N8RR, wrote: "3. Does anyone have practical
experience/suggestions for feeding antennas on separate towers in phase?"
The current issue of NCJ has a nice write-up by WX0B outlining his
stack-match[ing] system, which can be used to stack two or three antennas on
the same, or even on different towers, using equal-length feedlines.
73, --Glenn, KB1GW
>From Tony Brock-Fisher <fisher@hp-and.an.hp.com> Wed Jul 5 14:31:25 1995
From: Tony Brock-Fisher <fisher@hp-and.an.hp.com> (Tony Brock-Fisher)
Subject: Antenna Height vs Performance
Message-ID: <9507051331.AA12559@hp-and.an.hp.com>
It is said that "Big Antennas, High, are better than Small Ones, Low"
(attributed to K1VR).
The corolary is "Small Antennas, High, are better than Big Antennas Low".
(attributed to Field Day).
I would like to suggest a third concept:
"Any antenna, High, works better than you ever imagined, Low".
What I am trying to suggest is that the performance of horizontally
polarized antennas over real, irregular ground is not accurately
characterized or understood by merely studying elevation antenna
patterns.
Case in point: I have a pair of KT-34XA's, at 70 and 40 feet. I have been
working with them for a year now, trying to phase them for increased
performance to EU (add CONTEST word here). I have discovered that
the 30 foot difference in height results in a much greater difference
in performance than can be explained by the elevation pattern
differences.
As a nice general rule of thumb, from studying elevation patterns,
there is approximately 1 db increase in gain at low angles (like
8 degrees) for every 10 foot increase in height, on 20 meters.
So the elevation patterns predict that the 'XA at 70 feet should
be 3 db better that the 'XA at 40 feet.
Actual measurements show more like 6-10 db difference.
I propose the following hypothesis:
The elevation patterns are generated assuming a flat ground extending
around thee antenna. In fact, I do not have flat ground. Instead, it
has hills, and is populated with trees, buildings, and power lines.
Approximately 6 db of gain is achieved in horizontally polarized
antennas over ground due to the ground reflection adding to the
sky wave. This assumes that the ground reflection is also horizontally
polarized and somewhat in phase with the sky wave. The phase of the
ground reflection with respect to the sky wave will vary with
elevation angle.
I propose that at low heights (1/2 to 1 wavelength), the ground wave
'seen' by the antenna is not exactly horizontally polarized, and that
it is not even planar. I propose that it is in fact distorted by the
uneven effective ground terrain in front of the antenna. The antenna
is actually located in the near field of the scatterers located in
the ground plane. This results in very little contribution by the
ground wave to the antenna's performance.
As the antenna height is increased, the antenna moves from the near field
to the far field of the ground scatterers, and the ground wave becomes
planar and horizontally polarized again, such that it again
contributes to the antenna's performance in a positive way.
I would claim that this effect explains why increasing antenna height
has a greater positive effect on real antennas in real locations than
can be explained solely on the basis of elevation patterns.
Perhaps some real 'experts' out there could comment.
-Tony, K1KP, fisher@hp-and.an.hp.com
>From sellington" <sellington@mail.ssec.wisc.edu Wed Jul 5 15:25:34 1995
From: sellington" <sellington@mail.ssec.wisc.edu (sellington)
Subject: Antenna Height vs Performance
Message-ID: <n1407186099.16163@mail.ssec.wisc.edu>
Another possible effect is detuning of the antenna when it is close to
the ground. So, in addition to more ground-reflection loss at low angles
for a low antenna, the gain of the antenna may also be reduced. (NEC
should be able to predict these effects, though I haven't tried it yet.)
Scott K9MA
sellington@ssec.wisc.edu
>From Greg Becker <gb546@bard.edu> Wed Jul 5 15:41:09 1995
From: Greg Becker <gb546@bard.edu> (Greg Becker)
Subject: Message from K6OZL
Message-ID: <Pine.A32.3.91.950705103942.21417A-100000@core.bard.edu>
On Tue, 4 Jul 1995, J. S. Jarrett wrote:
> Someone owes Ron an apology, a public apology. Any men running this thing?
>
> On Sun, 2 Jul 1995, Brian Short wrote:
>
> > > I must appologize to the contest reflector. The message you read was
> > > sent as a private message
I'm confused. Why does someone owe Ron an apology, public or not, and
what's the "men" point?
73, Greg
Greg Becker NA2N
gb546@bard.edu
>From Rajiv Dewan <rdewan@uhura.cc.rochester.edu> Wed Jul 5 15:46:28 1995
From: Rajiv Dewan <rdewan@uhura.cc.rochester.edu> (Rajiv Dewan)
Subject: Antenna Height vs Performance
Message-ID: <199507051446.KAA17940@uhura.cc.rochester.edu>
Tony, K1KP wrote:
<snip>
> "Any antenna, High, works better than you ever imagined, Low".
>
> What I am trying to suggest is that the performance of horizontally
> polarized antennas over real, irregular ground is not accurately
> characterized or understood by merely studying elevation antenna
> patterns.
>
> Case in point: I have a pair of KT-34XA's, at 70 and 40 feet. I have been
> working with them for a year now, trying to phase them for increased
> performance to EU (add CONTEST word here). I have discovered that
> the 30 foot difference in height results in a much greater difference
> in performance than can be explained by the elevation pattern
> differences.
There is more science to antennas and propagation than we often
realize. This is a case to point. As Kraus, W8JK, showed in the
1930's, two dipole fed out of phase will lower the launch angle.
This is also true for stacked yagis. For simplicity, consider an
observer at zenith. The observer will see the 20m waves from bottom
yagi lag by almost 180 degrees (approx 30' in 20m band) and they
will cancel. So the radiation towards zenith decreases and those
at lower elevation angles decreases. Voila.
Rajiv, aa2ui, rdewan@uhura.cc.rochester.edu
>From Dan Ransom" <RANSOM@FOLEY.GONZAGA.EDU Wed Jul 5 16:49:15 1995
From: Dan Ransom" <RANSOM@FOLEY.GONZAGA.EDU (Dan Ransom)
Subject: Performance of Cushcraft 40-2CD above a tribander
Message-ID: <21E482A5947@FOLEY.GONZAGA.EDU>
> How about some comments from other contesters on their experiences
> in stacking the 40-2CD (or other 40M beams) above the KLM KT34XA,
> HyGain TH-7 or other favorite tribander?
No problems here at contest station K7MM in Spokane with a 40-2CD six
feet over a KT-34XA. It plays well with the KLM at 72 feet and the
Cushcraft at 78 feet. I have turned the 40-2CD 90 degrees (East) of
the KT-34XA to minimize the possibility of interaction. Performance
and SWR are great!
Dan Ransom K7MM
Ransom@Foley.Gonzaga.edu
>From Rich L. Boyd" <rlboyd@CapAccess.org Wed Jul 5 17:08:16 1995
From: Rich L. Boyd" <rlboyd@CapAccess.org (Rich L. Boyd)
Subject: 40 and tribanders
Message-ID: <Pine.SUN.3.91-FP.950705120647.12887G-100000@cap1.capaccess.org>
I visited local station W3HVQ, who has antennas on one tower that point
different directions, on the same rotator that is. He had an interesting
system, a lightweight cardboard secondary azimuth scale on a piece of
tape at the top, so it could be flipped down to show which direction one
antenna was pointing, or flipped up out of the way to show the other
antenna heading. It was taped to the top of his rotator indicator dial.
Rich Boyd KE3Q
On Wed, 5 Jul 1995, WF3T wrote:
> Anyone having trouble with interaction between a 40 and a tribander (usually
> 15) might want to try KLM's recommended practice of turning them 90 degs to
> each other. Taping another scale on the bottom of the meter solves
> late-in-the-contest mind fog problems. I am using a 40-2CD (100ft) and a
> KT34XA (90) like this, and SWR, performance, and pattern seems to be on a
> par with what should be expected from these antennas.
> 73,
> Steve WF3T
>
> *\* NOTE - NEW E-MAIL ADDRESS *\*
> *\* steve.steltzer@paonline.com (WF3T) *\*
> *\* "Relax, you'll get there." *\*
>
>From De Syam <syam@Glue.umd.edu> Wed Jul 5 17:15:54 1995
From: De Syam <syam@Glue.umd.edu> (De Syam)
Subject: July 8-9: Which contest do I play?
Message-ID: <Pine.SUN.3.91.950705121225.3667A-100000@espresso.eng.umd.edu>
This coming weekend presents a dilemma for me because there are
three contests on the calendar, each of which I would like to
participate in. So I did a comparagraph to see when I could
operate in one without affecting the others.
Here is what we are faced with:
IARU HF Contest: 1200Z Saturday 8 July - 1200Z Sunday 9 July
CQWW VHF Contest: 1800Z Saturday 8 July - 2100Z Sunday 9 July
FRACAP Contest: 1200Z Sunday 9 July - 2400Z Sunday 9 July
I expect the IARU contest will have the greatest amount of activity
so I will dedicate my full time to that one until it is over. I
won't be freed up for the CQWW VHF Contest until 1200Z Sunday, but
starting at that time gives me a good shot at the best time for 6
meters meteor scatter at least. Hopefully there will be good
Sporadic E on 6 between then and 2100Z Sunday also.
The FRACAP Contest is 40 meters only and daylight here from 2100-
2400Z makes it iffy that I can do much into Central America even
with a 3-el Yagi, but perhaps the last hour will yield something.
Decisions, decisions!
Very 73,
Fred Laun, K3ZO
>From lvn@fox.cen.com (Larry Novak) Wed Jul 5 17:51:34 1995
From: lvn@fox.cen.com (Larry Novak) (Larry Novak)
Subject: Antenna Height vs Performance
Message-ID: <9507051651.AA05869@cen.com>
>
> It is said that "Big Antennas, High, are better than Small Ones, Low"
> (attributed to K1VR).
>
> The corolary is "Small Antennas, High, are better than Big Antennas Low".
> (attributed to Field Day).
>
> I would like to suggest a third concept:
>
> "Any antenna, High, works better than you ever imagined, Low".
>
For the tower-impaired, another corollary:
A resonant antenna works better than a non-resonant antenna.
I put up a 20 meter quad loop at 60 feet just before the WPX CW
contest (I was using an 80 meter windom at 55 feet and a tuner). I
haven't modelled the 80 meter antenna to see what the theoretical
difference is but in practice, I'm seeing 3 S-units (15-18 dB) in
favored directions. I am literally hearing things on the loop that are
just background noise on the windom. It's also a much more effective
transmitting atenna.
i.e., get rid of your all-bander.
73, Larry, K3TLX
--
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-+
| Larry Novak \-\-\ email: lnovak@cen.com |
| Century Computing | Tel: (301) 953-3330 |
| 8101 Sandy Spring Road | Tel (@NRL): (202) 404-7682 |
| Laurel, MD 20707 | Fax: (301) 953-2368 |
| http://www.cen.com/ | Amateur Radio: K3TLX, C6AHE |
+=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-+
>From Larry Schimelpfenig <lschim@mailstorm.dot.gov> Wed Jul 5 17:57:22 1995
From: Larry Schimelpfenig <lschim@mailstorm.dot.gov> (Larry Schimelpfenig)
Subject: STACKING TRIBANDER AND 40-2CD
Message-ID: <Pine.3.07.9507051222.E27118-a100000@mailstorm.dot.gov>
Interesting reading. Mark KX3Q told me that when he stacked his 40-2CD 10
feet above his KT34XA at 100ft, it totally destroyed the XA's pattern on
15. He side mounted a 4 element 15 mtr monobander at 70 ft or so to get
around the problem. He tried swinging the 40 90 degrees from the XA to no
avail.
KLM's suggested spacing between the KT34XA and their 40 mtr antennas are
on the order of 6' between dipole and XA, 8' between 2el and XA, 12'
between 3el and XA, and 14 or 16' between 4el and XA. This is due to the
larger capacitive effects of the larger antennas. They also recommend they
be mounted 90 degrees from each other.
73 de Larry K7SV
lschim@mailstorm.dot.gov
>From Rich L. Boyd" <rlboyd@CapAccess.org Wed Jul 5 18:01:32 1995
From: Rich L. Boyd" <rlboyd@CapAccess.org (Rich L. Boyd)
Subject: Antenna Height vs Performance
Message-ID: <Pine.SUN.3.91-FP.950705130007.29463C-100000@cap1.capaccess.org>
At Dayton this year some guys did a great presentation on their highly
successful Field Day operation and they noted the "small antenna high
works better than a big antenna low" phenomenon. They hauled a
single-element 6 meter antenna (aluminum dipole) up high in a tree on a
rope and found it worked better than the beam they had been using lower
down (and went up easier and quicker too).
CONTEST
Rich Boyd KE3Q
>From ken silverman" <ken.silverman@ccmail.AirTouch.COM Wed Jul 5 19:29:45
>1995
From: ken silverman" <ken.silverman@ccmail.AirTouch.COM (ken silverman)
Subject: CQ Boston Contesters
Message-ID: <9506058049.AA804966052@ccmail.airtouch.com>
I will be in Marlboro, Mass July 16-21, and would like to get together
with ya-all for a visit.
I arrive in Boston on Sunday at 5PM. I'm also available after 5 PM,
from Monday through Thursday, and I will be glad to drive wherever.
73 and hope to CU soon,
Ken WM2C/6
President, Northern California Contest Club
>From Douglas S. Zwiebel" <0006489207@mcimail.com Wed Jul 5 18:58:00 1995
From: Douglas S. Zwiebel" <0006489207@mcimail.com (Douglas S. Zwiebel)
Subject: Low vs High
Message-ID: <84950705175848/0006489207PK3EM@MCIMAIL.COM>
I would question the method used to MEASURE the difference between
LOW and HIGH (or whatever). Several years ago I mounted an A4 tri-
bander on tower A at 55' and a 4L monobander at 55' on tower B. I went
through 10, 15, and 20 meters, using separate monobanders, one at
a time so that only ONE monobander was IN THE AIR at any given time
when comparing to the tribander. Cutting out all the reasons why I
did this, I can tell you that my first set of TESTS showed a huge
difference, something on the order of 2 to 2.5 S units. Now we all
know that a figure like that is "impossible" but that is what I got
when using the S meter on my rig. I posted my results on the NE mega-
cluster and got lots of flack (rightly so). I got one or two replies
that suggested I used something that was calibrated to measure it and
to run the tests again. And I did. I still found a large difference,
ranging 4-6db, but certainly nothing like 2.5 S units (whatever those
are). Anyhow, I concluded that I would stick with monobanders on
multiple towers rather than go to multiple stacked tribanders on multiple
towers. For me, 4 db was too much to give up. So I would suggest using
a calibrated instrument (I used a step attenuator with 1db steps) and be
sure that it really is calibrated. I had a friend at MCI measure mine
and it was +/- 0.15db. And be sure to remove all other variable too.
In my test setup, I even SWAPPED coax to remove that from consideration.
Finally, weird stuff can happen. Many years ago at K2GL's place (remember
the N2AA M/M operations?) we had the pleasure to play with LOTS of antennas
on LOTS (13) of towers. On ten meters, I got to play with antennas mounted
on 4 different towers. Two of the towers were 80' tall about 150' apart,
were the same height and same elevation. Both were 10 ele 10's. Then
we had a 10 over 10 stack "on the hill" which was about 70' higher than
everything else. The last was 5 over 5 fixed due South on 180' of 25,
but mounted at about 40 and 70 feet up. At any given time, any one of
the antennas could prevail. At time slot X, the stack on the hill could
be up 2 S-units and then 5 minutes later, to the same station, one of
"low" antennas would be 2 S-units up, then 5 minutes later it would revert
back the other way. It is really SPOOKY to find that type of difference
when using the two "low" towers compared to each other. They look the same,
same height, same elevation, same 10 ele yagis, just 150' apart. It made
no sense at all. LESSON: more antennas are better than less antennas, no
matter if high/low/near/far/vertical/horizontal/in the tree/in the clear/etc.
This is especially true for CONTESTING. Even a wire dipole or sloper for
10/15/20 can help at times. For you 1 tower guys, put up wires also! You
would be amazed how LOUD that ZD7 or VP8 can be on wire compared to your yagi
aimed at Europe!
[Greg: I like the pix of the kids in NCJ!]
de Doug
KR2Q@mcimail.com
>From barry@w2up.wells.com (barry) Wed Jul 5 19:20:37 1995
From: barry@w2up.wells.com (barry) (barry)
Subject: Feeding antennas...
Message-ID: <3g4R8c4w165w@w2up.wells.com>
"Swanson, Glenn, KB1GW" <gswanson@arrl.org> writes:
> The current issue of NCJ has a nice write-up by WX0B outlining his
> stack-match[ing] system, which can be used to stack two or three antennas on
> the same, or even on different towers, using equal-length feedlines.
>
> 73, --Glenn, KB1GW
DOn't think I've received the "current" issue yet, but I'm not starting
that discussion again...
Without seeing the article, it just doesn't make sense to phase antennas
on different towers unless they are fixed in direction. For example, say
you have two towers, one wavelength apart (for simplicity) as the crow
flies to Europe. By using equal coax lengths from the box, these antennas
are in phase. However, if you rotate the antennas, and point at JA, for
example, the driven elements of the two antennas are no longer a
wavelength apart, and the in-phase relationship is lost.
>From R. Torsten Clay" <torsten@mephisto.physics.uiuc.edu Wed Jul 5 20:22:57
>1995
From: R. Torsten Clay" <torsten@mephisto.physics.uiuc.edu (R. Torsten Clay)
Subject: Antenna Height vs Performance
Message-ID: <199507051922.AA14920@mephisto.physics.uiuc.edu>
>
> For the tower-impaired, another corollary:
>
> A resonant antenna works better than a non-resonant antenna.
>
> I put up a 20 meter quad loop at 60 feet just before the WPX CW
> contest (I was using an 80 meter windom at 55 feet and a tuner). I
> haven't modelled the 80 meter antenna to see what the theoretical
> difference is but in practice, I'm seeing 3 S-units (15-18 dB) in
> favored directions. I am literally hearing things on the loop that are
> just background noise on the windom. It's also a much more effective
> transmitting atenna.
>
> i.e., get rid of your all-bander.
>
> 73, Larry, K3TLX
>
Well, the all-band dipole I use has been better than almost all the other
simple wire antennas I've put up. It's 95 feet long and hangs between two
trees at about 65 feet up. The feed is open wire with a Johnson matchbox.
One problem with all-band dipoles is that on higher frequencies, the
elevation response can get kind of messy (ie some high-angle lobes). In
my case, on 20m there is a largish lobe at about 50 deg elevation. For a
while, I had a second dipole stacked at about 35 feet...feeding them in phase
then cleaned up some of the elevation response.
I would still highly recommend all-band dipoles, as long as they aren't fed
with coax (lossy!), or with a balun antenna tuner.
Tor
n4ogw@uiuc.edu
>From Peter G. Smith" <n4zr@netcom.com Wed Jul 5 19:32:39 1995
From: Peter G. Smith" <n4zr@netcom.com (Peter G. Smith)
Subject: Antenna Height vs Performance
Message-ID: <Pine.3.89.9507051120.A21466-0100000@netcom>
I think that the success you're having may have more to do with the loop,
per se, than with resonance or non-resonance -- my townhouse antenna was
a 280' vertical plane odd-shaped loop with the apex at about 55 feet, fed
at a lower corner with 450 ohm line, from a 4:1 balun and back to the
tuner on my 930. The tuner was able to kill the SWR on any band 80-10,
and it worked well on all of them. I was particularly pleased with how
much I could hear, compared to people with much more elaborate antennas.
And much to my surprise, it was several s-units better than an R5
vertical with its base at 10 feet above ground (in the trees, to be sure)
on every band except 10 meters. Go figure!
73, Pete
N4ZR@netcom.com
"Better, faster,cheaper -- choose any two"
"No no no -- it's WEST Virginia"
>From yvk@WOLFE.net (John KE7V) Wed Jul 5 20:54:35 1995
From: yvk@WOLFE.net (John KE7V) (John KE7V)
Subject: Hi vs low antenna
Message-ID: <199507051954.MAA05794@mail1.wolfe.net>
I'm still waiting for the person who will make the blackbox that
determines the actual angle of radiation at any moment, "arrival".
That way we can all design our towers and antenna systems to
automatically sense this angle and "voila". At W7RM the higher
antenna on 10-15 and 20 always listened better on the long haul
signals, but go to the caribbean and vice versa. W7RM was on a
bluff 200 feet or so over salt water, and who knows where the
ground was at.
73's Johnny KE7V
>From David O. Hachadorian" <74752.115@compuserve.com Wed Jul 5 21:55:08 1995
From: David O. Hachadorian" <74752.115@compuserve.com (David O. Hachadorian)
Subject: Antenna Height vs. Performance
Message-ID: <950705205508_74752.115_EHL231-1@CompuServe.COM>
On 5 July, Tony Brock-Fisher wrote:
> ...I propose that at low heights (1/2 to 1 wavelength), the ground
> wave 'seen' by the antenna is not exactly horizontally polarized,
> and that it is not even planar. I propose that it is in fact
> distorted by the uneven effective ground terrain in front of the
> antenna...
Tony's hypothesis rang a bell with me and I dusted off an
Engineering reference book from my old working days. This whole
section is kind of interesting, so I'll just go ahead and type it.
(sure wish I had a scanner/OCR software.) I hope you all find it
interesting in designing your CONTEST antennas.
The following symbols and definitions apply. Others are defined
in the text.
h = antenna height in meters
& = takeoff angle = TOA (author used symbol psi-subscript-zero.)
# = wavelength in meters (author used symbol lambda.)
$ = angle subtended by an obstruction (author used psi subscr. obs.)
@ = effective height with sloping terrain (author used h subscr slope.)
The following is an excerpt from:
Richard C. Johnson and Henry Jasik, "Antenna Applications
Reference Guide," part of "McGraw Hill Engineering
Reference Guide Series," Second Edition, McGraw Hill Publishing
Co., New York, New York, 1986.
> 3-8 SITING CRITERIA FOR HIGH-FREQUENCY ANTENNAS
> ___________________________________________________
>
> In the preceding sections it has been assumed that the
> antenna is mounted over a smooth, level ground plane of infinite
> extent. However, an actual antenna site is seldom smooth and level,
> and sites which approximate ideal conditions usually do so only
> over a limited area. In addition, the effects of co-sited antennas
> and of natural or artificial obstructions can result in degradation
> of antenna performance. This section assesses the effects of
> imperfect sites following closely refs. 26 and 27, and presents
> practical criteria for obtaining acceptable performance.
>
> Fresnel Zone and Formation of Antenna Beam
>
> The main lobe of a transmitting or receiving antenna
> (the following discussion applies to both)
> is formed by the interaction of the direct
> radiation of the antenna and the reflected radiation from the
> ground plane. Reflections occurring near the antenna are of
> greater importance than those occurring far away. With a
> directional antenna, radiation at or near boresight angles is more
> important than that occurring at azimuth angles away from boresight.
> From these facts, it follows that there is an elliptically
> shaped area (with the major axis in the direction of the main lobe,
> as shown in Fig. 3-27) in which the ground must be level and smooth
> if the first lobe is to be formed without appreciable distortion.
> From simple geometrical ray theory it is clear that as the
> TOA is decreased, the lengths of the major and minor axes of the
> elliptical area increase. The curvature of the earth also affects
> the size of the axes, but it can be ignored if the TOA is more
> than 3 degrees.
> The ellipse dimensions are different for vertical and
> horizontal polarization and in the former case are difficult to
> evaluate. Fortunately, the dimensions for horizontal polarization,
> which are easy to evaluate, give a reasonable approximation for
> the vertically polarized case. The ellipse dimensions correspond
> to the first Fresnel zone, which is the region in front of the
> antenna in which direct and reflected radiation differ in phase
> by 180 degrees or less. For horizontal polarization, if the
> antenna has a TOA of &, the radiation will appear to come from a
> height above ground of
>
> h = (#/4) sin & (3-16)
>
> The distance from this radiation point to the near and far edges
> of the first Fresnel zone, denoted by dn and df respectively
> are given by
>
>
> h 2.828
> dn = ----- x (3 - ----- ) (3-17)
> tan & cos &
>
>
> df = (same equation as above, except substitute a plus sign for
> the minus sign in the second part.) (3-18)
>
> The maximum width of the Fresnel ellipse is
>
> w = 5.66h (3-19)
>
> Equations (3-16) to (3-19) may be used to calculate, to a
> very good approximation, the area of flat, unobstructed land
> required in front of a directive antenna to ensure that the main
> lobe is fully formed. For very low TOA the Fresnel zone may
> extend for several kilometers, and it will not usually be possible
> to contain the zone within the boundaries of the antenna site.
> If the size of the controlled area is to be reduced, it is possible
> to limit it to the region in which the phase difference between
> the direct and reflected radiation is 90 degrees or less. In this
> case, there may be a loss of gain of up to 3 dB, but the
> dimensions of the ellipse will be reduced as follows:
>
> df may be reduced to 0.6 times the full value.
>
> dn may be increased to 1.6 times the full value.
>
> w may be reduced to 0.7 times the full value.
>
>
> Roughness in the First Fresnel Zone
>
> In the zone with dimensions given in Eqs. (3-16) to (3-19), the
> main lobe is approximately fully formed provided the ground is flat
> and smooth. However, if the ground is rough or has natural or
> artificial obstructions or depressions, reflection will not be
> specular. The reflected wave will be scattered, and there will be
> a loss of gain and distortion of the beam. Rayleigh's criterion
> indicates that the transition between specular and scattered
> reflection occurs when the maximum height H of deviations above
> and below the average terrain profile does exceed
>
> H = h/4 (3-20)
>
> This criterion may be relaxed if additional degradation in
> performance is acceptable. The relaxed criteria are based
> on the reasonable assumption that the permissable size of
> the obstructions may increase with distance from the
> antenna. It is usual to divide the first Fresnel zone into
> three regions, within which the heights of obstructions and
> depths of depressions should not exceed the values in the
> accompanying table.
>
>
> _______________________________________________________________
>
> Limit of departure from Region of first
> average smooth terrain Fresnel zone
> ---------------------------------------------------------------
> H/4 dn to 0.2 df
>
> H/2 0.2 df to 0.6 df
>
> H 0.6 df to 1.0 df
>
> ________________________________________________________________
>
>
> It is difficult to predict with precision the degradation
> that occurs when the above criteria are applied, partly because
> the shapes of the obstructions have been ignored. However, it is
> reasonable to expect gain losses of several decibels. These
> criteria apply to cases in which the entire first Fresnel zone is
> rough. When a major portion of it is smooth, somewhat larger
> obstacles can be tolerated if they do not cover more than 5 to
> 10% of the zone. Caution must be exercised, however, when
> compromises in controlled area size and roughness are made
> simultaneously because gain reductions may then become large.
>
>
> Horizon Obstructions
>
> Obstructions beyond the first Fresnel zone at distance D >> df
> can reduce radiation at low angles even if the first Fresnel
> zone is perfectly smooth. If the height of the obstruction is H,
> antenna performance will not be noticeably degraded if the angle
> subtended by the obstruction as viewed from the antenna,
> $ = inverse tan (H/D), is less than 0.5 times the lower half-power
> point of the antenna elevation pattern. For TOAs of less than 30
> degrees, this criterion is given by
>
> $ < &/4
>
> Terrain Slope
>
> If the ground at an antenna site slopes down in the direction of
> radiation by an angle b, the TOA is decreased from & (the value
> for a flat site) to & - b. Conversely, if the ground slopes up
> in the direction of radiation, the TOA becomes & + b. Fresnel-
> zone theory can be applied to sloping sites by using the following
> modified antenna height factor:
>
> @ = #/4 sin (& plus/minus b) (3-21)
>
> in Eqs. (3-16) to (3-19). The plus sign is used for upward slopes;
> the minus sign, for downward slopes.
>
> Ground Conductivity
>
> For vertically polarized antennas, high ground conductivity is
> important for the effective operation of transmitting antennas,
> as explained in Sec. 3-2. Vertical transmitting antennas
> mounted very near seawater, which has a high conductivity of
> 4 S/m, do not require ground screens for radiation-pattern
> enhancement. For most types of soil, conductivity is is
> significantly smaller than this value, so metallic ground
> screens are necessary. For horizontally polarized antennas, good
> ground conductivity is not important unless the TOA is very high,
> as explained in Sec. 3-2.
To address Tony's question, I guess equation 3-20 says that if the
hills in the first Fresnel zone are in the order of 1/4 of your
antenna height, you can expect less than the full 6dB augmentation
from ground reflection. Hopefully Tony will expand on the details of
his terrain and see if this explains the big difference between his
antennas at 70 and 40 feet.
Dave, K6LL
74752.115@compuserve.com
>From ken silverman" <ken.silverman@ccmail.AirTouch.COM Wed Jul 5 23:02:40
>1995
From: ken silverman" <ken.silverman@ccmail.AirTouch.COM (ken silverman)
Subject: Low vs High
Message-ID: <9506058049.AA804978105@ccmail.airtouch.com>
> A4 ..showed a huge difference, something on the order of 2 to 2.5 S units.
You are assuming that the A4 actually has gain over a dipole. If the A-4 traps
are lossy, then you could have 6-8 dB of difference. There's not much info out
there that substantiates the mfg's claims on gain...
But we all tend to look at ONE gain figure, that of maximum, and it usually is
on the horizon. What we tend to forget is that the E-Plane (elevation plane) of
the antenna will also impact the signal level. The monobander could have had
more gain in the "Right" elevation point during your tests.
>For you 1 tower guys, put up wires also! You
would be amazed how LOUD that ZD7 or VP8 can be on wire compared to your yagi
aimed at Europe!
Great point.
At C6AHX M/S in the CQ WW CW, while running USA, we "double beamed" on 15m with
the 5 ele tribander faced at USA, and a sloping dipole at 30' towards Africa
(because we figured that the Africa path was going to be open during the
afternoon while we wanted to run USA). It was worth a bunch of African mults
that we simply couldnt hear on the yagi when it was pointed to the USA.
Ken WM2C
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