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Author Topic: Antenna for portable work (near sea coastline)  (Read 10151 times)
9A5BDP
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Posts: 224




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« on: February 21, 2011, 11:18:53 AM »

Hi there...

I want to prepare my portable kit for work during next summer. Please advise me on one matter..
Will be beter for me to use vertical 8m (26 ft) fishing rod antenna with ATU or multiband switched wire dipole in
inverted V configuration. My portable QTH will be placed some 150m ASL and aprox 2 km (or using old but trusty american units one and something miles) from Adriatic coast line. I will be using TX with 20w output (Collins manpack PRC515).
If you have some good ideas for another type of DIY antenna please make note for me..

Thanx in advance

73!
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KB4QAA
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Posts: 3342




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« Reply #1 on: February 21, 2011, 01:31:23 PM »

Antenna type doesn't matter.  Generally the closer to the water the better.

Enjoy your trip.
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.
2E0OZI
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Posts: 270




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« Reply #2 on: February 21, 2011, 02:36:56 PM »

I have heard of people doing really well with a vertical as you describe, on the beach, with an earth wire running into the sea!

I live only 10 minutes walk from a beach and soon enough as the weather improves I am going to get some type of portable opeartion going there from time to time for fun.
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Men can only be happy when they do not assume that the object of life is happiness.
George Orwell
KI6CQ
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Posts: 15




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« Reply #3 on: February 21, 2011, 02:44:22 PM »

In Southern California I go to the ocean, about 50-100m from the water, with the following:

  • * beach spike for Jackite pole
  • * Jackite plastic telescoping pole, 9m fully extended
  • * vertical driven element -- a 26 gauge wire tied to top of jackite pole, dangles down to center pin PL259
  • * autotuner with 2 ground radial wires
  • * 15m rg8x coax from autotuner to radio
  • * 15m computer serial cabe from autotuner to radio
  • * 10Ah 14V 20A LiFePO4 battery with battery monitor in small shielded box
  • * Icom 706-Mk2G


Everything but the pole and spike fits in a toolbox. The radio is mounted on a mobile mount inside the toolbox and a number of connections made to reduce the number of connections that need to be done on site.  The IC706Mk2G was chosen for the ability to use a remote head for control. This has worked for me on 40m-10m.  You will hear things right at the
ocean that you will not hear inland with the same setup. 

73 Paul KI6CQ
 
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WB6BYU
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Posts: 18516




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« Reply #4 on: February 21, 2011, 03:28:03 PM »

2km is too far away to get the enhancement from vertical polarization over salt water.
For best effect you should be within 10 to 20m of the water.

My guess is that you will have better results as you describe using dipoles or inverted vees.
My portable kit has dipole wires for all bands and a center insulator with coax cable (8m of
RG-174 coax.)  I attach any combination of wires that I want to use to the insulator and
string them up in the trees.

If you are on the side of a hill, by choosing the optimum height for your inverted vee you can
maximize low angle radiation in the direction down the hill.

If you have trees available that would allow you to get your antenna up higher than your
mast.  Sometimes a delta loop is convenient for this - string the top between two trees
as high as you can throw a rock.  The feedline connects at the bottom of the loop.  This
lets you get your antenna up higher for the same maximum length of feedline.
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9A5BDP
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Posts: 224




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« Reply #5 on: February 21, 2011, 11:06:36 PM »

Hi..
Last year I try inverted V configuration but performance was bad. I am thinkig that is main cause for this in using aluminium centre pole, maybe this pole was radiating also...hmm. This year I make plan to use something else. Trees in near surroundings do not exist, only partialy covered terrain with small bushes. Ground is rocky based with some sand and earth. My main sea direction is to side of Africa, other directions have 'hill' obstacles.
Last night one antenna catch my eyes..T2FD in vertical polarisation (mounted on fishing pole)...no radials needed..needing more advice about this configuration.
What kind of antenna is in the bag of goodies for DX IOTA activators?

Thanx for all for now..

73!
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WB6BYU
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Posts: 18516




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« Reply #6 on: February 22, 2011, 06:51:52 AM »

The T2FD tends to be an inefficient antenna, about 5 to 6dB down due to losses in the
terminating resistor (and much worse when the antenna is less than about 1/3 wavelength
long.)  Generally I would not recommend one unless the wide-band match with low SWR
is more important than signal strength.

In rocky soil with poor conductivity a vertical antenna will usually perform poorly.  But
sometimes you just have to experiment with different antennas and see what works best
at your location - even a good antenna won't work well when propagation is poor.
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9A5BDP
Member

Posts: 224




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« Reply #7 on: February 22, 2011, 08:12:22 AM »

Reading on net what people saying about T2 antennas became clearly visible basic problem of that principle of operation..resistor and disipating wast of power on them.
So I must go to basics...rude and primitive but works...wire (switchable) dipole or perhaps G5RV antenna. On my planed QTH near sea I have dificulties to put antenna in inv V cofiguration because it is near inpossible to put one leg of inv V over local road...but with some inginuity maybe I gain success.
Making right choice for building portable antenna is dificult task for me because my portable qth is far away from my main qth and workshop that I have by home. One possible solution is to make several different antennas (vertical and horisontal wires) and to try what will be better in actual conditions.
If any of you ham gurus have some idea for portable antena please share thouts with me...

73!
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WB6BYU
Member

Posts: 18516




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« Reply #8 on: February 22, 2011, 09:06:29 AM »

Take a large spool of wire with you, with some extra rope, feedline and insulators.  Then you can
make many different types of antennas - even if the connections aren't soldered you can still see
how well they work.

This is one advantage of my dipole kit:  it has wires for 80, 40, 20, 15 and 10m, and I can use
them in other ways because they are not permanently attached to the coax.  For example I
have used one 40m wire (10m long) as a full wave loop for 10m (it required that I add 1 50cm
clip lead for SSB and two for CW.)  Another time I strung up the 20m dipole between two
rocks where the ground dropped nearly 100m between them, and made the 40 and 80m wires
into parallel-conductor feedline to reach to the radio.  I have had good results with full wave
loops, which can be arranged for either horizontal or vertical polarization, as well as various
long wires, end fed half waves, and even a 15m J-pole.  It all depends what best fits your
available space.
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KE5DFK
Member

Posts: 55




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« Reply #9 on: March 03, 2011, 08:54:44 AM »

I like to drive to NA092 and operate from the beach.  I run a home brew mobile antenna that found in an old QST article, this thing flat out works great parked within 20ft of the surf.  I have worked a good number of EU and Russian states with it. 
No reason why you could not ground mount it.  Link to the ARRL article        http://www.arrl.org/files/file/Technology/tis/info/pdf/0004033.pdf


What I prefer to use at the beach is my custom Hustler 4BVT.  Works even better than the above antenna.  Custom, well I drive a Jeep and everything has to fit inside my Jeep and 7ft poles will not fit, so I cut the long sections in half.  I contacted Hustler and told them what I wanted to do and if they had aluminum tubing that would fit inside the long sections of the antenna.  For $25 they cut me the tube I needed and even included 4 hose clamps that I would need to get the antenna back to the original length.  The entire antenna fits inside of a camping chair bag and added only 2 or 3 lbs to the original weight of the antenna.  I have a radial plate that I made but at the beach I don't use it.  NA092 has some of the most conductive soil anywhere.  It takes about 15mt to but back together and operational. 

It all depends on how portable you want to be.  For 20w antenna is everything.

Good Luck
Carlos
KE5DFK
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VE3WMB
Member

Posts: 332




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« Reply #10 on: March 10, 2011, 08:05:39 AM »

It is hard to beat an 88 ft doublet, center-fed with open-wire line, ladderline or even TV Twin lead to an autotuner. This is an Extended Double Zepp for 20m and will yield gain of about 9 dBi broadside on 20m.  You mention that the QTH is rocky so you want to stay away from vertical polarization. You will want to put the antenna up as a flattop at least 1/2 wavelength (on 20m) if you want the gain and a low radiation angle. Using an inverted vee will make the pattern more omni-directional and will kill the added gain. This antenna should match from 80m through to 10m with a decent auto-tuner.

http://www.tomochka.com/na7u/doublet/w4rnlbackup.html

If you can take advantage of sloping terrain and a clear shot at the ocean, putting the antenna part-way down the hill (as opposed to at the top) will further enhance the signals in the direction opposite to the hillside.

Michael VE3WMB

P.S. If you do manage to operate from the beach near the waterline then be sure to use a vertical.
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