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Author Topic: Field Day antennas  (Read 1643 times)
WB6BYU
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Posts: 13147




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« on: April 30, 2013, 12:04:51 PM »

It's that time of year to think about antennas for Field Day (unless, of course,
you are like me and think about them all year long...)

I thought I'd open a thread for a general discussion of the topic:  what has
worked for you in the past, what you'd like to try, suggestions for specific
situations, etc.

Please remember that everybody is in a different situation, so there is no one
single antenna that works for everyone.  This also means that, if you are asking
for suggestions, it is good to mention the constraints / operating conditions that
you expect to encounter:  types, location and heights of available supports;
distances and directions you want to cover; resources available to install the
antenna;  and other constraints such as cost, size, weight, transportability,
setup time, etc.


In my case, operating from Oregon means that we aim our antennas due East, and
most of our contacts are within about a +/-30 degree span at distances of 1000 miles
or more.  I DON'T want an omnidirectional antenna for maximum effectiveness:
a 3- to 4-element yagi is about right, up high enough to get significant radiation at angles
below 30 degrees,even on 40m and 80m.  (Closer stuff is easy enough to work off
the sides of the beam.)  This is a very different situation than a station in, say, Ohio
or Tennessee, where there are significant numbers of stations in most directions and
over shorter distances.

I'm currently looking at broadside arrays that can be hung from trees:  I haven't yet
determined whether we'll have regrowth firs in the 60 - 70' range or older ones that
will allow antennas much higher at our site.  (I can throw a rope to 60' but 120' will
require a pneumatic tennis ball launcher.)

In previous years I've used dipoles, yagis, a horizontal full-wave loop, and a 40m
doublet.  The doublet was something quick and simple just to get the CW station
on the air, and worked about as well as anything else.  This year I'm considering
a stacked pair of them.  I'm also looking at folding the sides forwards about 15 degrees
or so to improve performance on 15m.  I contribute my triband yagi to the SSB
station (they need all the help they can get) but also have some designs for wire
yagis and quads if the supports are suitable.


What are you planning to try this year?  Do you have a situation that you need
suggestions for?
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K9SRV
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Posts: 121




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« Reply #1 on: April 30, 2013, 12:51:57 PM »

just to toss an idea out to get this thing rolling, how about a 80 meter V Beam,pointed East,Fed with Ladder Line to a balanced tuner? Should work most bands and what would ideal would be to make a plan to then rotate it south and follow the sun.... Just my .02. If it is lame idea, feel free to point that out. I am here to learn, so giveaway. I would be esp. interested in hearing any new ideas using wire.I WILL say my 40 meter des works great for me, but I am in the Midwest.Anyone have an idea how to use that antenna with a reflector or director to send his signal East only, with gain?   John K9SRV
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WB6BYU
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Posts: 13147




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« Reply #2 on: April 30, 2013, 10:12:29 PM »

Quote from: K9SRV

...how about a 80 meter V Beam,pointed East,Fed with Ladder Line to a balanced tuner?



I still have the vee beam with 185' legs that we used a couple years.  We hung the feedpoint
from the highest support available and sloped the legs down to near ground level (exact height
depended on the length of rope on the end of the wire.)  This allowed us to rotate one or both
legs easily to vary the pattern.

While such an antenna is capable of some gain, the sloping wires aren't as effective as making
them horizontal, as the average gain suffers and ground loss increases due to the lower average
height.  In practice we didn't notice much difference when we rotated the pattern, so I left it
at about 120 degrees between the wires, allowing effective operation on 80m and 160m.  We
still seemed to make as many contacts on the higher bands in spite of the lower theoretical
gain.

With 185' legs it is capable of a bit of gain over a dipole on 80m, but not enough to make
up for the reduced average height:  an inverted vee works better unless you can get the
feedpoint up a half wavelength or so and the ends up close to that.  On 40m with the
feedpoint at 40' it works about as well as a horizontal dipole at the same height.  Also
the F/B ratio is almost non-existant.

It's one of a number of antennas that sound impressive but don't actually work very well.



Quote

...Anyone have an idea how to use that antenna with a reflector or director to send his signal East only, with gain? 



There are several common methods:  you can build an identical antenna with a carefully-
chosen length of shorted stub, or use a standard reflector wire (somewhat longer than
1/2 wave) behind each end of the antenna, with a rope connecting them to string them
in a line.

Hmmm...  I happen to have a model of a 40m version right here at a height of 60 feet: 
with 70' reflector wires (#12) spaced 25' behind each end of the antenna, it gives a
fairly clean pattern (all stray lobes down about 15dB or so) with 12.55dBi gain, which is
nearly 3dB better than the EDZ itself without the reflector.  My design also added a 130'
wire spaced 45' behind the antenna (and centered on it) to act as a reflector on 80m. 
The main lobe is rather narrow, with a 3dB beamwidth of only 36 degrees (down 9dB at
+/- 30 degrees) which is just barely wide enough to cover the East coast from here,
and would be even more limited from your location if you want to cover NY to FL.

A handy tool is the NS6T azimuthal map, available online here: 

http://ns6t.net/azimuth/azimuth.html

I printed one up based on our Field Day location then overlaid it with pattern plots
from EZNEC to get a good idea of the expected coverage area of various antennas.
I also had a plot of a dipole at the same height, and it was surprising how many
case there were (G5RV, OCFD, etc.) where the dipole gave as good or better
performance when you averaged it over the desired coverage area, especially
on the higher bands where the pattern breaks up into multiple lobes.
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K9SRV
Member

Posts: 121




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« Reply #3 on: May 01, 2013, 07:18:13 AM »

Wow, looks like the wrong guy responded... Grin  You seem to have put much more effort and thought into the antennas than I have.... you bring up some good points, but I wonder how much better the v beam would perform if the legs were completely horizontal....  john
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W1JKA
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Posts: 1621




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« Reply #4 on: May 01, 2013, 08:23:17 AM »

 Great topic: I'm always interested in what the other boys are using and results from their FD antennas.I mostly operate QRP/CW portable so mostly everyday is basically a field day for me.For the past 4 years I have built and experimented with all the basic wire antenna types and configurations. My priorities are quick set up,directional ability,light weight/small size,no tuning or SWR meters and good performance on 40,30 and 20M,the only bands I'm interested in. For the past year I have settled on MY own "ultimate" FD/portable antenna which best suits my needs in the New England environment for the following reasons.It is the simple inverted Vee with the legs also in a sloping Vee and a 28 ft. length of light 8X coax with a simple CVC plumbing tee for the center connector and wing nut conections for my 3 sets of radiator wires.The radiators are precut and tuned at the home QTH for each band to a 1.5:1 SWR at a 12-15 ft. height,in the field this gives me a SWR range between 1.2:1up to 3:1 depending on different ground conditions with no negative effect on my QRP rigs.Mast or center supports are no problem,plenty of trees and 20 ft.deadfall fir or spruce saplings for a a quick tripod mast lashed together at top with an old military web belt I carry for just such a purpose.For a while I carried a Cabela's 16 ft. crappie pole around for a center mast it was a PITA and found it was not needed.Antenna is easily rotated for direction on interest by moviing the sloping Vee legs.Mostly I use it mono band but sometimes use it as a type of fan Vee for two bands with no interaction problems.With this set up I get my fill of CONUS stations on 20m during the day and the usual morning/nite grey line DX on 30M.Works for me.
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EI2HEB
Member

Posts: 53




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« Reply #5 on: May 02, 2013, 01:54:04 AM »

Hi all,

Just to share what I use on Field Days.
First of all, the local radio club, the North Cork Radio Group (www.ei1nc.com) organizes field days and events all year round, with an average of once monthly. So, like the OP, I am thinking of portable antenna's all year round as well.

As a beginner in the hobby I had to make choices of what I need at first, and build my arsenal as time goes by.
I built a 1/4-wave vertical with ground radials for 40 meter, tuned it to be at 7.170, and used this at first for 15m (with tuner) and 40m.
The drawback was the time to setup the antenna (about an hour) and that it will take a minimum of 3 people to do so, especially in high winds.

This year I added a MFJ993BRT tuner at the feedpoint of this vertical, this allowed me to tune any band. Not surprisingly we got some great results on 20m, where this would be close to a half-wave!

I still keep and use this antenna, despite the difficult setup and time.

Secondary antenna I have is a short aluminium push-up mast of about 3 meter height. On top a Chameleon V2, extended with a Chameleon MIL whip. Used two telescopic MFJ rods as a GP. With a Tuner it will rune from 10 to 20m. But it seems that best results of this antenna are 15m.
The drawback of this antenna is that the Chameleon is a "compromise" antenna. The great benefit of this antenna is its quick setup time; mast and antenna operational in about 10 minutes!!

These are the two protable setups I am currently using.

Plans are there for a collection of wire dipoles, which I am building now. And I have some thoughts on a more directional setup, something like a foldable Hexbeam, on a tall push-up mast.... but budgets need to be observed as well !!

I am sure that my collection of antennas will grow over time...

73,
EI2HEB - Edwin.
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WB6BYU
Member

Posts: 13147




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« Reply #6 on: May 02, 2013, 08:03:28 AM »

Quote from: K9SRV

I wonder how much better the v beam would perform if the legs were completely horizontal.... 



I used the same 185' wire lengths with the feedpoint and ends at 40' on 20m.  At the
optimum angle between the wires the gain was 12.5dBi, compared to 7.8dBi for a dipole
at the same height, 9.5dBi for a 40m doublet (2 half waves in phase), and 10.8dBi for
an EDZ (without a reflector.)

But the half power beamwidth for the vee beam was 20 degrees with a number of side
lobes and perhaps 3dB F/B ratio.  The beamwidth for the dipole was 84 degrees,
54 degrees for the two half waves in phase, and 39 degrees for the EDZ.

So the vee beam might be good for targeting New England, for example, but not as good
for a larger target area.

By contrast a Moxon at the same height gives about 11dBi gain, >20dB F/B, and a half
power beamwidth of 79 degrees, besides being much smaller!


So, as usual, choice of antenna will depend a lot on the supports and materials you have
available.  It is harder to rotate a horizontal vee beam, especially when it is in among
other trees (though it can be done with some creative use of ropes when it is in an open
space among trees.)  The beamwidth is narrow, but if all you have is wire and rope it
might not be a bad choice.  But you could hang wire quad or yagi elements from a rope
and get more gain with a wider beamwidth using less wire, though it isn't as good for
multiband operation.
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WB6BYU
Member

Posts: 13147




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« Reply #7 on: May 02, 2013, 08:10:51 AM »

Quote from: EI2HEB

I built a 1/4-wave vertical with ground radials for 40 meter, tuned it to be at 7.170, and used this at first for 15m (with tuner) and 40m.
The drawback was the time to setup the antenna (about an hour) and that it will take a minimum of 3 people to do so, especially in high winds.



Hmmm...  then perhaps the setup process and/or mechanical construction can be improved.

I use 4' sectional mast sections (military surplus) and it takes about that long to put a tri-band
yagi up at 28'.  I wanted to show I could do it myself one year, but another ham insisted on
helping.  It is, of course, easier to put up just the mast.

The secret that makes it easy is to use a sectional (or telescoping) radiator and to stack the
sections vertically, rather than trying to tilt up the completed assembly.  For example, I check
the various disposals and second-hand stores for old aluminium tent poles, about 2cm across,
typically in 32" lengths.  I use these for lightweight portable VHF masts, but they would also
work as a radiator.   I tie the guy ropes to the top section and stake them out to the approximate
locations, then carry the top section out until two of the guy ropes are tight:  at that point I
should be able to lean the mast against the pull of the two guy ropes to hold it up while I grab
the next section.

Then I pick up the mast while moving slightly close to the guy anchors, so the mast can keep
leaning slightly against the ropes, slip the next section on the bottom of the stack, and put it
down.  Yes, it's a bit easier if you have someone else to hand sections to you, but I've put
up 40' of the heavier mast sections by myself.  Takes some practice to get the feel of how far
you need to lean the mast against the guy ropes, but once you do it can go up pretty fast.
Once it is vertical you can adjust the guy ropes and move the base sideways to the desired
position.

When we put the beam on top we start by putting up just the mast and getting the guy ropes
all set out, then lower it, put the antenna on, and put it back up.  And hopefully we don't have
to lower it again because we forgot to connect the coax...
« Last Edit: May 02, 2013, 08:17:56 AM by WB6BYU » Logged
EI2HEB
Member

Posts: 53




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« Reply #8 on: May 02, 2013, 12:25:04 PM »


  I tie the guy ropes to the top section and stake them out to the approximate
locations, then carry the top section out until two of the guy ropes are tight:  at that point I
should be able to lean the mast against the pull of the two guy ropes to hold it up while I grab
the next section.

Then I pick up the mast while moving slightly close to the guy anchors, so the mast can keep
leaning slightly against the ropes, slip the next section on the bottom of the stack, and put it
down. 


Very interesting technique; I will certainly practice this on a calm day, and see if this improves from the "tilt all technique" !
Thanks!
EI2HEB - Edwin.
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WB6BYU
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Posts: 13147




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« Reply #9 on: May 02, 2013, 08:28:17 PM »

The 4' sections are about the longest practical length for a person of reasonable height
to put it up standing on the ground.  A bit shorter would be better - a metre is probably
ideal.

If it is windy then try to arrange it so that the mast is downwind of the guy anchors so
the wind pushes against them rather than tipping the mast sideways.  (For maximum
strength once it is up, however, the ideal would be to have one guy straight into the wind.
But if we are pushing the guy ropes or anchors that much, we probably shouldn't be trying
to put up an antenna.)
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WB6BYU
Member

Posts: 13147




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« Reply #10 on: May 03, 2013, 01:00:49 PM »

Quote from: W1JKA

...the simple inverted Vee with the legs also in a sloping Vee and a 28 ft. length of light 8X coax with a simple CVC plumbing tee for the center connector and wing nut conections for my 3 sets of radiator wires...



My backpack portable antenna kit is very similar, with wires for 80, 40, 20, 15 and 10m:  it
predates the WARC bands.  I use 25' of RG-174 coax and a center insulator made from a slice
of radiator hose.  The ARES HF antenna kits I build use heavier materials, but the same
basic principles for 40 / 80 / 160m.

A single support (mast or rope over a tree) and the wire ends tied off with ropes to any
convenient bush or rock provides convenient operation without needing a tuner, while the
wires can be reconfigured in more creative ways when it fits the situation.

Actually a dipole isn't a bad antenna choice for Field Day in many cases, especially if it is
high enough in the air (not as important for those closer to the center of population.)  I used
to have to be on call during Field Day, so I operated 1E from my house with inverted vees for
40 and 80m and a rotatable dipole (the driven element from my triband yagi) for 20/15/10.
I worked 45 states one year using dipoles and QRP, in about 8 hours of operation.


But when I go out with the local club I like to do what I can to make use of the terrain, space
and supports available to maximize performance.  Many hams can only dream of having a
full-sized 80m dipole up high and in the clear, so I like them to have an opportunity to see
what it can do.  It also sets an example of how effective a full-sized antenna can be, as my
funky wires run rings around the shortened commercial "portable" antennas that others have
brought out to use.  I've got 24 hours to set up antennas beforehand, and plan to make the
most of it.

There are a couple different design philosophies:  antennas that work multiple bands, or
optimizing it for a specific band.  Until I get a good look at the site and we decide where the
various stations will be located I don't know what I have to work with.  For 80m a dipole up
high may be sufficient, or a delta loop with the feedpoint at the bottom if the space between
convenient tall trees is a bit short otherwise.  (That gets the main portion of the radiator higher
in the air for the same length of feedline.)  An 80m doublet can be used on 40m to get some
broadside gain, but I've also built 2- and 3-element wire quads for 40m that work well with tall
enough supports.  A full-wave 80m loop worked pretty well, with 4 lobes at right angles:  one
pointing East and the others up and down the West coast, thought the pattern tended to be
rather sharp on 15m and 10m.

At one site I had the opportunity to string some horizontal antennas over a road, and considered
various types of wire yagi and quad designs suspended from a single top rope.  While those tend
to be monoband antennas, several can be installed from a single rope "boom".  (In the end, due to
bad weather and having to hobble around on crutches, I tossed up a quick 40m doublet in a
nearby tree instead, and it worked quite well.)

Of course there have been some overly-ambitious projects that weren't worth the work that
went into them.  The 6-element log-delta loop array that we strung up in the dark Friday night
was a great example:  it sure looked impressive, but worked almost as well as a dipole.  And the
only redeeming function of the 600' long wire we tried was sending the really annoying guy to go
untie the other end when we took it down - he didn't know how long it was, or how far down the
hill into the bushes it went, and it kept him out of our hair for quite some time.

So now I'm looking at various 40/20m broadside arrays to see what sort of supports they would
require, and considering what I would use in case I need to be vertically polarized (to reduce the
RF interference among stations.)  But, who knows - I may end up with a dipole again, depending
where the Field Day Coordinator decides to place the CW station.
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