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Author Topic: Lobe pattern for kite antenna long wire  (Read 1949 times)
2WOHMS
Member

Posts: 8




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« on: January 28, 2013, 01:11:51 PM »

Hello gentlemen, I'm after some advice on the lobe pattern that I would obtain on my kite antenna for 20, 17 and 15m

The kite antenna wire is 40.3 metres in length, terminates into a 9:1 balun and the rig does my final tuning via built in ATU.

My contacts on 20,17 and 15 are sporadic to say the least, 40 and 80 seem OK, not yet worked the evening shift on 160 though.

The take off angle for the wire is very much wind strength dependent but is generally 50 - 80 degrees from horizontal and I'm fairly sure that on 20/17 and 15 the angle is next to useless.
If I sloped the wire via some pulling loop to  30 deg or less, would I see a worthwhile improvement on 20/17/15 ?

Any advice would be most appreciated.
Thanking you in anticipation
Eugene  2W0HMS
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WB6BYU
Member

Posts: 13231




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« Reply #1 on: January 28, 2013, 01:35:48 PM »

Yes, it may very well be too long for the higher bands.

I'm sure the data for radiation patterns from various wire lengths are available online
somewhere, but I have these numbers handy for the approximate angle of maximum
radiation relative to broadside for a 40m wire:

80m  0 degrees
40m  50 degrees
20m  60 degrees
15m  63 degrees
10m  68 degrees

So if your wire is 20 to 30 degrees above the horizon or less, maximum radiation will
be at low angles.  If the wire rises too much, then maximum radiation goes straight
into the Earth, or off into space.

One problem with this is that the radiation pattern is quite directional:  because the
pattern forms a cone around the antenna, only in the direction of the wire (both
ends) will you get low angle radiation.  You'll have some higher lobes off to the
side from that a bit, but not much in other directions.

And those patterns assume a straight wire, which isn't usually the case for kites
that I have flown in any sort of wind.  Actual patterns will be more complicated.


This is why long wire antennas work much better when installed horizontally than
a sloping or inverted vee configuration.
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2WOHMS
Member

Posts: 8




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« Reply #2 on: January 28, 2013, 02:43:49 PM »

Many thanks for you input.
I'm not too bothered about the directional aspect - I work the kite from a beach and any DX is just fine for the log, I just want more QSO's. on more bands
I'm relieved that to some degree (excuse the pun) the situation can be improved by altering the line angle, any thoughts  on what realistic improvement could be achieved ?

I assume that the pattern of 0 degrees for 80 M  is parallel to ground, and 160 also requires a line angle near as vertical as possible, am I correct ?
Tnx   2W0HMS
 
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WB6BYU
Member

Posts: 13231




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« Reply #3 on: January 28, 2013, 03:02:08 PM »

160m isn't as critical:  your antenna is 1/4 wave, so most of the radiation will
be from the bottom portion.  (You may want to eliminate the 9 : 1 transformer,
however, as the impedance will probably be 30 - 50 ohms without it.)  It's just
too short on 160m to have much directivity.

On 80m keeping it more vertical would be good for DX, while sloping will be
better for more local work.  Again, the wire is only 1/2 wave, so the current
is in phase throughout the wire length.

Once a wire gets to about 3/4 wavelength there is more than one portion with
high current, and the currents are out of phase in adjacent half wave segments.
With the wire being a full wave on 40m, for example, the radiation from the upper
half is out of phase with that from the lower half, which puts a null on the horizon.
That's the root cause of problems with the wire being too long.

The simplest solution is to use a shorter wire on the higher bands: 6m to 7m is
a good upper limit on 10m for a vertical, up to twice that for 20m.  You can probably
got a bit more than that, since the antenna usually will be sloping.

You might run the kit up 20 - 40m or so on a string, then attach the antenna wire
to the string and let it hang down to the ground (perhaps with a second string
to take the strain if the kite pulls too hard.  That gets the kite up high enough to
have reliable winds without needing the wire to be too long.  (I never trust my wire
to fly the kite - the string is stronger.)
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W5WSS
Member

Posts: 1723




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« Reply #4 on: January 28, 2013, 05:02:42 PM »

Yes use shorter length wire. let the wire and balloon pull against a dead end of 1/4 wave radials.

I did exactly this at a summer cottage and preferred the quarter wave length pulled tight and mostly vertical.

I made up some 1/4 wave lengths for all the bands and could quickly change the antenna wire,but one could choose anywhere from 1/4 wave to 5/8 wave with the addition of a wide range tuner for all but the quarter wave.

The quarter wave and elevated tuned radials 2 per band worked really well and I did not need a tuner.

Dead ending the far end of the radials with non conductive anchors to hold the radials taught while the balloon pulls.

I eventually opted for a tree limb.

Use a wander lead and earthing rod to bypass the antenna wire to the rod when expecting thunderstorms.

Long DX Contacts were easy and very numerous.

73
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WB6BYU
Member

Posts: 13231




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« Reply #5 on: January 28, 2013, 05:15:25 PM »

Quote from: W5WSS

Use a wander lead and earthing rod to bypass the antenna wire to the rod when expecting thunderstorms.



Good advice to ALWAYS have a static ground on the antenna wire, even when
you are using it and no storms are in sight.  You can get a pretty good static
charge built up.  A large wire-wound resistor - say 10K at 10W - from your antenna
wire to ground, or the use of a tuner with a shunt coil, can save you some surprises.
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2WOHMS
Member

Posts: 8




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« Reply #6 on: January 29, 2013, 12:12:12 AM »

May thanks to each of you for your sage advice
I should ahve
Quote from: W5WSS

Use a wander lead and earthing rod to bypass the antenna wire to the rod when expecting thunderstorms.



Good advice to ALWAYS have a static ground on the antenna wire, even when
you are using it and no storms are in sight.  You can get a pretty good static
charge built up.  A large wire-wound resistor - say 10K at 10W - from your antenna
wire to ground, or the use of a tuner with a shunt coil, can save you some surprises.

Thanks, I'm using a 1 Megaohm @ 5 Watt non inductive resistor to ground for prevention of nasty surprises.
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2WOHMS
Member

Posts: 8




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« Reply #7 on: January 29, 2013, 12:20:08 AM »

160m isn't as critical:  your antenna is 1/4 wave, so most of the radiation will
be from the bottom portion.  (You may want to eliminate the 9 : 1 transformer,
however, as the impedance will probably be 30 - 50 ohms without it.)  It's just
too short on 160m to have much directivity.

On 80m keeping it more vertical would be good for DX, while sloping will be
better for more local work.  Again, the wire is only 1/2 wave, so the current
is in phase throughout the wire length.

Once a wire gets to about 3/4 wavelength there is more than one portion with
high current, and the currents are out of phase in adjacent half wave segments.
With the wire being a full wave on 40m, for example, the radiation from the upper
half is out of phase with that from the lower half, which puts a null on the horizon.
That's the root cause of problems with the wire being too long.

The simplest solution is to use a shorter wire on the higher bands: 6m to 7m is
a good upper limit on 10m for a vertical, up to twice that for 20m.  You can probably
got a bit more than that, since the antenna usually will be sloping.

You might run the kit up 20 - 40m or so on a string, then attach the antenna wire
to the string and let it hang down to the ground (perhaps with a second string
to take the strain if the kite pulls too hard.  That gets the kite up high enough to
have reliable winds without needing the wire to be too long.  (I never trust my wire
to fly the kite - the string is stronger.)

Thanks again, I'm lucky to have a reply from someone with kite experience (no disrespect intended to other valuable contributors)
Interesting about taking the balun out of circuit on 160, I'll give it a try.
You mention at the end of the first paragraph "It's just too short on 160m to have directivity".Could you clarify ?
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2WOHMS
Member

Posts: 8




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« Reply #8 on: January 29, 2013, 12:22:06 AM »

Yes use shorter length wire. let the wire and balloon pull against a dead end of 1/4 wave radials.

I did exactly this at a summer cottage and preferred the quarter wave length pulled tight and mostly vertical.

I made up some 1/4 wave lengths for all the bands and could quickly change the antenna wire,but one could choose anywhere from 1/4 wave to 5/8 wave with the addition of a wide range tuner for all but the quarter wave.

The quarter wave and elevated tuned radials 2 per band worked really well and I did not need a tuner.

Dead ending the far end of the radials with non conductive anchors to hold the radials taught while the balloon pulls.

I eventually opted for a tree limb.

Tnx, I'll try what you've done

Use a wander lead and earthing rod to bypass the antenna wire to the rod when expecting thunderstorms.

Long DX Contacts were easy and very numerous.

73
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N8BOA
Member

Posts: 90




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« Reply #9 on: January 29, 2013, 04:05:21 AM »

I have pondered what to fly many times since I tried a balloon during FD years ago with not so good results. With longer may not be better in mind. You need to get the radiating put of the antenna up were the kite is. If it has the lift capacity try lifting some twin lead or light weight ladder line with ½ wave wire of the lowest freq you will operate at the end of one of the ends. Yes the old zep antenna or as the VHFs call them J-pole
Have fun
Be safe stay away from those power lines
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WB6BYU
Member

Posts: 13231




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« Reply #10 on: January 29, 2013, 12:39:41 PM »

Height is important for VHF, local work on 10m, or for horizontally polarized
antennas.  It isn't as important (and, in fact, can be counter productive) for
vertically polarized antennas over salt water ground, as it introduces more
nulls into the vertical radiation pattern.  So choice of antenna will depend
to a large part on where you are operating:  working DX on 20m may
require a high horizontal antenna over land, but a low vertical over salt
water.

Using a Zepp feed / J-pole isn't a bad approach, at least for one band at
a time.  you can use a half wave wire radiator, a quarter wave of twinlead
for the matching section, then regular coax from there to the ground:  the
coax may be heavy enough to limit how high the kit can pull up the antenna,
which may be a good thing:  it certainly is easier than trying to keep the kite
at the right height so the wire doesn't pull off of the tuner.  You would want
to keep the kite high enough so the matching section doesn't lay on the
ground.

In practice you need to keep the kit up at some minimum height where the
breeze is steady, which is why i prefer to tie the antenna to the string some
distance down from the kite.

Certainly one method is to have a spool of bare wire, let out as much as you
want to use, and connect it to the tuner with a wander lead if you are
planning to operate multiple bands with a single antenna.  Otherwise there
are a number of options that just use the kit as a "sky hook" to hold it up,
such as Bruce's original Inverted Vee (vertical half rhombic), vertical loops,
ground planes, colinear arrays made with folded wires, etc.  A common
problem is the weight (and wind resistance) of the feedline if you try to
elevate the feedpoint much above the ground.
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N8BOA
Member

Posts: 90




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« Reply #11 on: January 30, 2013, 08:37:49 AM »

wrote "a quarter wave of twinlead for the matching section," a 3/4 wave or any odd mult should match to
Or KISS use a tuner but you will have feed line radiation when outside of the 1/4
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