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Author Topic: Longwire -160m-6  (Read 914 times)
ZS5SWT
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Posts: 2




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« on: June 17, 2006, 10:38:08 AM »

I have a longwire to go up onto my AH4 icom tuner.

I have read good results from 102" up to 257'mentioned on various postings .
My problem is that I mainly want the lower bands(160/80/40) to have the better preformance and space is not limited .From the tuner @ 8' ,the run of wire will take a 45 degree slant to nearby trees at about 65 '. the wire can then make its way back to the far end  about 8'off the ground. I have total lengh of +- 300 to 600 feet .(100 to 200m)
Any suggestions on the ideal lengh.
Regards Brad ZS5SWT
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KC4GS
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« Reply #1 on: June 17, 2006, 11:07:33 AM »

I am of the idea that the longer the better.  More wire, more signal picked up.  Of course you will have to use a tuner on it, and you will need a good ground close to the tuner.  Here it is the shorter the better.
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KB4QAA
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« Reply #2 on: June 17, 2006, 11:18:48 AM »

Well, if you are putting up a longwire, make it as long as you can.  

Remember the AH-4 restriction about not trying to tune up/xmit on 1/2 wavelength or even multiples thereof the antenna length.

Bill
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K0BG
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« Reply #3 on: June 17, 2006, 11:29:04 AM »

As pointed out, the AH-4 won't tune 1/2 wave lengths, or any multiple. The lengths to stay away from are listed in the manual (if you can call one sheet a manual).

And be aware, at loads over about 3K ohms, the output shunt capacitance is fixed. As the impedance goes over 3K, the input SWR also increases to about 2.5 at 5K ohms. Further, the RF voltage gets rather high (about 10KV), and normal insulators will not suffice, and you always run the risk of arcing over one of the relays. In other words, you need to follow Icom's suggestion.

Alan, KØBG
www.k0bg.com
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W8JI
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« Reply #4 on: June 17, 2006, 12:14:20 PM »

As you make a longwire longer a number of things happen.

First, the pattern becomes more directional along the general direction of the wire. Signal is focused along the wire's direction.

Second, the antenna becomes much lossier. At about 2 or 3 wavelengths loss actually goes up faster than the increased directivity would normally increase gain. This means at some point gain peaks and then beyond that length gain starts dropping off.

Third, the impedance stops going through large changes with frequency. The antenna tends to stabilize around 400-500 ohms and not change much with length.

Some of these things are good, some are bad. Longer is not always better, especially if you can't point the wire into the general direction you want to work.

As a general rule we don't want to make the longwire longer than 2 or 3 wavelengths, or shorter than 1/2 wave although other lengths will work. If you have unlimited room, you might want to install several different longwires in different directions or with different lengths.

73 Tom
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WA1RNE
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« Reply #5 on: June 17, 2006, 01:14:44 PM »

 FYI, the Icom AH4 is not designed for 160, but will tune 80-6 meters.


 The AT-180 tuner will run down to 1.9 Mc but not sure if this is low enough for you.


 Assuming your lower frequency tuning limit is 80 meters,  you could try multiples of 0.33 wavelength or ~120 degrees to avoid feeding a voltage point (very high Z) or a current point which migh be too low an impedance for the tuner.


 For 80 and 40, you could use approx. 445 feet and the tuner should be happy.


  73,  Chris
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W9OY
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« Reply #6 on: June 17, 2006, 02:24:13 PM »

What about the counterpoise?    

You might find it better to pick a spot about 25ft from the base of the tree and plant a 4x4 and use this as a common point to run some (20-30) nice long (maybe 100ft) radials.  Then run up several different near vertical pieces of wire into the tree, a 1/4 wave for 80, a 1/2 wave for 40 and an inverted-L for 160.  Feed each one seperately through a coax switch.  Use the radials as a common counterpoise for all 3 wires.  You will need some kind of parallel network for the 40M wire, but the others you should be able to tune to resonance by pruning.    

Same tree, same amount of wire, likely better performance, and no worry about RF in the shack.  You will also be able to tune the 80M on 30M with good results using your tuner.  This will get you excellent performance on 160, 80, 40, and 30.  You can use the 160 inv-L as a long wire on the higher bands if you want.  130ft is about 2 wavelengths on 20, 2.5 on 17 and 3 wavelengths on 15 etc.


73  W9OY
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ZS5SWT
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« Reply #7 on: June 17, 2006, 02:38:50 PM »

Thanks to all that have responded.I am using the AH-4 tuner from Icom .
I have used multiple faned dipoles for 40/80 before , have thought of using two feeds off the tuner at a slight angle offset. Of the two wire lenghths , one being  half of the first.This could get around the 1/2 wavelength problems associated with the tuner.I am certainly no expert so am always thinking of ideas.
 There are just so many "theories on the long wire antenna situation that one can go round in circles.

I look forward to any further suggestions.REGARDS BRAD
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K0ZN
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« Reply #8 on: June 17, 2006, 04:07:32 PM »


Hi.

If you can find one of the older ARRL Antenna Books (from early to late 1960's) they have a better and more detailed section and commentary on true long wire antennas. Properly installed they are good antennas, but directional. The longer the antenna, the greater the directivity effects.

You will need to figure out where and what you need for signal coverage and direction before installing a particular type of antenna.

Good luck....

73,  K0ZN
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KA5N
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« Reply #9 on: June 17, 2006, 06:34:18 PM »

If you have all that room, have you considered a horizontal loop?  Easier to match to, multiband coverage, works well fairly close to the ground.  Less noise since it is a loop, etc.
Allen
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K4SAV
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« Reply #10 on: June 19, 2006, 06:58:02 AM »

..." There are just so many "theories on the long wire antenna situation that one can go round in circles."...

--------------
That's because it is a complicated antenna.

You can do like most do, just put it up and see what happens, or you can try to figure out what is going to happen.  It's then, that you discover it's complicated.

If you feed it with a single wire with no ground system, then you will have a lot of RF in the shack, as much as on the antenna. You, your equipment, and your house wiring will be the other half of the antenna. This is very likely to be a problem unless you are running QRP.  It will also be very noisy on receive.

If you install a ground system outside, and feed it with a single wire against ground, it will operate like a long wire on the high bands, and on 80 and 160 it will operate approximately like a vertical in one direction and in other directions it will act like a low dipole except with a null overhead.  Gain will be low on these bands. This option usually requires a remote tuner.

If you feed it like an end fed zepp, which requires a quarter wave matching section at the end, it will look like a long wire on the band where the matching section is a quarter wave. On other high bands it will basically have a long wire pattern but with lower gain. The ARRL antenna book has more information on this option. In all cases there will be a considerable amount of RF coming down the feedline to your radio unless you install a good ground system and decouple to it.  Removing this feedline common mode current can get complicated.

A long wire pattern has very narrow lobes.  You have to point the antenna toward the ONE direction you want.  It will operate poorly in all other directions. If you have several of these and can select them, then it can become a general purpose antenna. Of course if you have several of these, a better option would be to configure them as a set of vee-beams.

Also the impedance of a long wire changes rapidly with frequency, requiring frequent readjustment of the tuner.

Jerry, K4SAV
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WB6BYU
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« Reply #11 on: June 19, 2006, 01:24:52 PM »

Are you more interested in local or DX contacts?

For local working on 80 or 160m I'd try to put a point
of maximum current about at the top of the antenna.  For
DX it should be in the sloping part or closer to the
feedpoint.

For efficiency you want the wire length to be at least
1/4 wavelength on 160m.

Especially when the wire is sloping, performance will drop
off on the higher bands as the wire gets longer.  It would
be best in that regard if the wire could continue horizontally
from the top of the tree rather than sloping back down
to the ground.

I'd probably shoot for something just under a half wave
on 160 - maybe 220 feet.
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