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Author Topic: 160M Antenna Coil-HOW?  (Read 3493 times)
KU2US
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Posts: 74




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« on: November 30, 2007, 09:23:22 PM »

I would like to do 160 meters. Its a challenge and fun. I am lot size restricted and would like to know how to wind a coil on each side, for a 160 meter dipole as to shorten it physically to fit in my yard. Any set formula or guidelines would be most appreciated. I have about 100 feet of yard length to play with.. Thanks in advance..Ken  KU2US   dentron1@yahoo.com
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N6AJR
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« Reply #1 on: November 30, 2007, 09:29:28 PM »

I ended up with a gap voyager for 40/80/160 duties, and decent low band vert and only requires 3 "radials" of 56 feet . and it works pretty good to boot.
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AC5E
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Posts: 3585




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« Reply #2 on: December 01, 2007, 04:49:25 AM »

I will second the GAP Voyager. Before Katrina I had one, and worked 65 countries on 160 without trying very hard. Never home near sunrise/sunset - so I took what I could get.  

No it's not a great 160M antenna: like all compromise antennas it has a restricted bandwidth so you should order it from GAP with the capacitor for the 160M band segment you intend to operate: and it is very flexible.

Scary flexible if you are trying to man it up yourself. Not so bad if you have a couple of friends pulling on the  guy ropes - yes you will need guy ropes - and it does surprisingly well on 160, 75, and 40. A lot better than the loaded dipoles I compared it to. The Voyager does not do so well from 40 on up, though.

And when you deal with GAP - keeping a smile in your voice works a lot better than gall.

73  Pete Allen  AC5E
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KZ1X
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« Reply #3 on: December 01, 2007, 05:55:40 AM »

The question you ask, how to wind a coil to shorten the legs of the dipole, has to be answered in context.  First, I can't recommend to most people using a dipole on top band.  The average ham can't easily get a 160 dipole high enough off the ground for it to radiate where you want.  I have 100' tall supports and my old full-size 160 dipole wasn't worth a darn.  Next, with the extreme size limitations you have, the heavily-loaded dipole you'd create with big coils will be, um, well, not all that effective.  Too much loss.  That is not to mention the mechanical challenge of building such a load inductor to withstand the physical stresses.

Other options abound, however, and some other posts talk about one.  

In a ~100' run, for another example, you could build a traveling-wave type antenna, such as that described by Ted N9NB back in the 80s in a HR article.    It's inefficient (comparatively speaking) but has the right pattern, and you can always make up for an inefficient antenna with a good pattern.

What sort of supports do you have?  How high are they?
What sort of clear area do you have to work in?  Don't skimp on details, remember, you have only text to work with here and you need to paint a picture of your entire setup using only words.  With this information, some other suggestions can be made that could result in a great experience.
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AC5E
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« Reply #4 on: December 01, 2007, 07:45:29 AM »

With somewhat more time let me add to my previous comments. To make it as simple as possible and possibly simpler than it really should be, 160 Meters is close to the "electron gyro" frequency. For most of North America, horizontally polarized signals get trapped by the Earth's magnetic field.

That field tilts toward the ground, and the further North you go the more the field is tilted. Therefore, for most of this area, horizontally polarized 160 M signals tend toward "one hop" propagation and then bore into the ground instead of being reflected.

I'm just a few miles from the Gulf of Mexico but even here a dipole is not a bad 160 antenna for a limited area ragchew group who want to keep on talking after sunset when 75 goes long. But I had better luck talking to the ham up the state with a vertically polarized 160 antenna than any dipole.

Conditions are different elsewhere. Dipoles do really well in the Indonesian archipelago; in much of South America; and so on. A couple of broadcast engineers I talk to who specialize in tropical band antennas systems were amazed at the difference in propagation characteristics between here and there

Bottom line - even a very compact vertical will outplay a dipole over most of North America.

73  Pete Allen  AC5E
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N3OX
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Posts: 8847


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« Reply #5 on: December 01, 2007, 08:10:32 AM »

If you want to try it anyway, download the programs

ADDALOAD

and

SOLNOID3

from here:

http://www.zerobeat.net/G4FGQ/page3.html#S301%22

ADDALOAD will tell you the coil value in microhenries you need to resonate your antenna.  ADDALOAD assumes you're trying to resonate a HALF of a dipole... that is, the wire length you're inputting is one half of the length you can fit in your yard.  You tell it the frequency you want and the physical location of the loading coil as a fraction of the length you input (0.5, mid-loading) is a good compromise between efficiency and coil size.

SOLNOID3 will tell you the inductance of a coil with certain physical dimensions and I've found it useful to build loading coils.  You have to put in a guess if you're shooting for a particular inductance value.  You should shoot for a coil that's 1 to 2 times as long as its diameter.

To get you started, I think you need about 47 turns #14 wire on a 4" form spaced evenly over 4" in the middle of each leg of a 100 foot dipole to get it on 160m.... that one might be a little heavy, by the time you add a coil form you'll be pushing a pound...

Anyway, I agree with comments that a low dipole won't be great... I'd consider an inverted L myself, of course it needs good radials... but I think an inverted L that has the same top height as your proposed dipole will beat that dipole, domestic or DX.  

Dan

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
KB4QAA
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Posts: 2450




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« Reply #6 on: December 01, 2007, 09:29:01 AM »

Read W4RNL, LB Cebik's article on choosing your first 160M antennna.  He has a treasure trove of antenna knowledge.

http://www.cebik.com/wire/160new.html

Bill
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W5DXP
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Posts: 3639


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« Reply #7 on: December 01, 2007, 01:29:38 PM »

The VF of a 6" dia., 4 TPI coil on 160m would be about 0.02. Whatever number of degrees you want the coil to occupy, wind it accordingly.
--
73, Cecil, w5dxp.com
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WA1RNE
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Posts: 828




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« Reply #8 on: December 01, 2007, 02:23:31 PM »


 You didn't say what the height is of available supports for a dipole. If it's in the 30-50 foot range, the antenna will be good for local contacts, for all the reasons indicated by others.

 The ARRL provides details online for designing practical loaded dipoles. Just use the chart at figure 2; http://www.arrl.org/tis/info/HTML/limited_space/limited1.html

 i.e. To design a dipole for 160 that's 50% of full size, or about 130 feet, a loading coil could be inserted at approx. 35% of length on each side or about 22.75'. Each coil would need about 734 ohms of inductive reactance, or about 65uH. Then you will need to design the coils: choose a diameter, form type (PVC, etc.) calculate the number of turns, etc. to obtain the required inductance.
 

 However, if you're looking for DX, as others have also said, a vertical is the way to go - especially on this band. Your best bet would be a top loaded T antenna as this requires no loading coils and keeps losses to a minimum. For a short vertical 40' tall, the horizontal part of the "T" would be about 47' long strung between 2 trees or other supports. The feedpoint runs about 23-25 ohms, so an L network or 1:2 balun will be required to match it to 50 ohms line. You will of course need a good radial system otherwise ground losses will be high and efficiency will be very low.

As they say, good DX antennas on this band ain't easy, but with the right calculations a good primary support system for the vertical and some patience you can pull it off.
 
 ...WA1RNE
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W8JI
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« Reply #9 on: December 03, 2007, 05:30:49 AM »

I work 160 all the time. I have for over 44 years!

I have dozens of antennas spread over a hundred acres, and I have lived on city lots. I have known dozens of people who work DX.

Don't believe anything that implies 160 or any band or any antenna is a "light switch" that either works or does not.

I've worked, and I know others who have worked, sucessfully many long distance contacts with a low dipole. W2EQS (sk), in the 1960's, was second place for DXCC on 160 with a 50 foot high dipole. Now my tall 220 foot vertical with 100 radials is maybe 1 S unit ahead of my high dipole for DX most of the time, but it certainly doesn't mean the dipole won't work! For most closer contacts they are equal.

The popular GAP is a VERY POOR antenna for 160. It is on par with a good mobile antenna for radiating efficiency. I had a Gap here, and walking out to my truck and using my mobile antenna produced about the same signal level.

It was 20 dB down from my normal vertical, a 100 foot tower. This proves even a very poor antenna can make people happy and provide contacts.

A Butternut is actually a better vertical.

A coil loaded dipole will work and almost certainly be much better than a Gap at any distance, but it will have disadvantages. You will have bandwidth problems, it will be narrow. You will likely have moisture problems or electrical or mechanical problems with the loading coils.

On the other hand if you are in an urban environment the dipole will probably hear much better than a vertical.

If I was in your position I would probably think of an Inverted L, a dipole fed with ladder line, or an end fed Zepp. I would install whatever ground system I could and feed any of three against ground for 160, and use them on other bands.

At one point I had a 130 foot vertical with 100 radials in a rich black wet soil. I had a friend who lived in the city and he had an 80 meter end fed zepp that was 50 feet high. When he fed that zepp as a end fed on 160 by tying the feedline wires together, he was within a few dB of me at any distance.  

You will get a lot of well intentioned advice, but the fact is you really need to make a choice based on your particular lot. A coil loaded dipole will absolutely work. So will a Gap. But whatever you choose has to fit your lot, and you probably should choose something with reasonable efficiency to start with. Virtually any vertical except the resistor loaded broadband models would be better than a GAP, but the gap still might make you happy.

73 Tom  
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WA3SKN
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Posts: 5526




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« Reply #10 on: December 03, 2007, 10:37:23 AM »

Just about EVERYBODY has a compromise antenna on 160!
Verticals need radials.  Dipoles need height.
Have you considered a linearly loaded Loop?
As for coils, there was an old "rule of thumb" that used twice the wire (about 1/2wavelength on 160 = 80 meters, or 240 ft of wire), space wound (one wire spacing between turns), with the length and diameter of the coil about equal.  Mount these in the center of each leg of the dipole.  Then, adjust the ends for resonance.  I haven't built any for 160... so you are on your own here!
Simple fact... have lots of wire, you will be using it!
Good Luck!

-Mike.

ps: I would try a loop design first!
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KC8ODH
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« Reply #11 on: January 08, 2008, 06:27:33 AM »

look up kc8qgj 1\2 wave 160m dipole with coil
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