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1-10 of 11 messages
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Fan -40-75-160????
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by WA3IRJ on November 2, 2005
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Hello all
As I stated in a prior post. I am home brewing a fan for 40-75-160.
I was going to use coils, on the end of the 75 meter wire...for 160m
But...I was also considering doing the 160m full size half wave.
This will give me some space issues. As the rear property offers just enough room for the 75 meter in an inverted V config.
But...How would it be, if I did the 160 meter in and in-V, and came down to the sides of the property, and ran the 160 meter ends along a 10 foot (wood) fence.
I guess it should be in opposite directions. The rest of the fan would be in the same configuration, except the ends would be about 12 feet from the ground.
This would be ceneter fed with 50ohm coax. The apex could be as high as 60 feet.
thoughts??
Kb3lxy
JohnB
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RE: Fan -40-75-160????
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by WB2WIK on November 3, 2005
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That will work fine. Having the ends so close to the ground on 160 will end-load the antenna almost assuredly, and if you cut the 160m wires "per the formula," I'll bet they turn out to be too long. No big deal, since you'll probably be able to reach them and trim them shorter as required.
Parallel dipoles usually have some interaction anyway, requiring site-tuning, so expect to spend an hour or more pruning and trimming. But the results will be worth it, and at 60' it should work pretty well.
WB2WIK/6
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RE: Fan -40-75-160????
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by K4SAV on November 3, 2005
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Building a fan antenna is a compromise game. The more elements you add, the lower the feedpoint impedance becomes at each resonant point. That means the SWR goes up and so does the ground loss if your antenna is low. Since your antennas will be low, ground loss will be significant, especially the 160 meter antenna that has half its length at 12 feet above ground.
Here are a couple of quick simulations to illustrate the point. Antenna 1 is a 160/80/40 fan like you described, and antenna 2 is the same antenna with the 160 meter portion removed. Coax loss is for 150 feet of RG213. Efficiency includes the coax loss plus ground loss.
_______________________Ant 1_____Ant 2
_____________________160/80/40____80/40
160M Res ohms_____________-_______19
160M SWR_________________-_______1.8
160M Gnd loss ohms_________-_______14
160M coax loss Db__________-_______0.5
160M Eff %________________-________23
80M Res ohms____________34________22
80M SWR________________1.75_____1.3
80M Gnd loss ohms________11________7
80M coax loss dB__________0.7______0.6
80M Eff %________________57________59
40M Res ohms____________18_______155
40M SWR ________________1.8______3.3
40M Gnd loss ohms_________2_______neg.
40M coax loss dB___________1_______1.4
40M Eff %_________________63________72
(I don't know how you make a decent table on this reflector. It deletes all your spaces and changes the character widths, and what you see is never what you get)
Notice the high feedpoint impedance for 40 meters on antenna 2. This will vary a lot depending upon exactly how close you have the wires. This high impedance creates most of the loss on 40 meters for antenna 2.
The elements all interact, especially as a function of how close the wires are, so you will have to prune them to resonance. Don't cut your wires too early, just fold them back onto the wire until you find the right lengths.
If you can find a way to get the portions of the 160 meter antenna higher, it will help a lot. The height is the reason that the efficiency on 160 is down to 23%.
Jerry, K4SAV
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RE: Fan -40-75-160????
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by WA3IRJ on November 3, 2005
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Thanks...
then there could be plan #2
Use two wires on the fan. One for 40 one for 75, with coils for 160. It will make 160 a little narrow..but with a decent tuner it may be workable.
That way, I can use it as a flat top. Or at least an
inverted v, and get the ends up 20-25 feet.
This may improve the impedence...picture. Some pruning as with any home brew, but it may radiate a little better. Small lots are hell! LOL
JohnB
kb3lxy
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RE: Fan -40-75-160????
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by WA3IRJ on November 3, 2005
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Thanks...
then there could be plan #2
Use two wires on the fan. One for 40 one for 75, with coils for 160. It will make 160 a little narrow..but with a decent tuner it may be workable.
That way, I can use it as a flat top. Or at least an
inverted v, and get the ends up 20-25 feet.
This may improve the impedence...picture. Some pruning as with any home brew, but it may radiate a little better. Small lots are hell! LOL
JohnB
kb3lxy
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RE: Fan -40-75-160????
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by K4SAV on November 4, 2005
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I see my table got messed up. The column lables are interchanged. I recompiled the table, and moved the 40M antenna so that it slopes to about 7 feet below the other wires to give a more reasonable result for 40M. I then readjusted wire lengths to bring both antennas back to the same resonant frequency. The numbers are slightly different from the first table.
________________________Ant2_____Ant 1
________________________80/40___160/80/40
160M Res ohms ____________-________16
160M SWR_________________-________2.1
160M Gnd loss ohms_________-________12
160M coax loss Db__________-________0.5
160M Eff %_________________-________22
80M Res ohms_____________43________26
80M SWR________________1.2________1.9
80M Gnd loss ohms_________10________7
80M coax loss dB_________0.6________0.7
80M Eff %________________67________62
40M Res ohms____________20________14
40M SWR_______________1.8________3.5
40M Gnd loss ohms________<.5________1
40M coax loss dB__________1________1.5
40M Eff %________________79________65
Jerry, K4SAV
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RE: Fan -40-75-160????
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by WA3IRJ on November 4, 2005
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No free lunch !
Would I just be better off cutting something off set, like a windom? And maybe the tuner will bring it more in line? And be more efficient?
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RE: Fan -40-75-160????
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by KE6VG on November 10, 2005
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Instead of loading coils on 160 you would still be better off bending the wire around or drooping the ends or something. Loading coils are a last resort. Been there done that.
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RE: Fan -40-75-160????
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by WB6BYU on November 11, 2005
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The simplest thing is to use a dipole for each band on a
common feedpoint. If you run the wires in different
directions (rather than keeping them all in one bundle)
then there is little interaction among the wires, and
they should work as well as a normal dipole. Spreading
them apart makes adjustment much easier.
If you don't have room for 160m, even after bending the
wires, then I'd suggest getting a pair of 40m traps and
using one wire for 40/160 and the other for 80m. Rather
than traps, you may find that a loading coil for 160m
is large enough that is acts pretty much like a trap
(depending on the distributed capacitance of the coil.)
But at least you can get the 40 and 75m wires up and
working while you decide how best to implement 160m.
A Windom won't work any better than a dipole, and likely
will need a tuner. And it still needs to be the same
length to cover the same bands.
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RE: Fan -40-75-160????
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by KB3LXY on November 29, 2005
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That is pretty much what I intended.
I have a Alpa delta DXCC. It is a 10-80 fan. It uses coils for 80 meter's on the same wire of the 40 meter.
I am going to do away with the 10-20 meter wires...add a full size 75 meter...and add wire behond the coils of the forty meter section..in an attemp to make it resonate on 160. My guess it will beed about 32 feet, at each end to get it in the right area. That will make it about 135 feet total length. Then trim from there. And spread the wire like a bow arrangement. I will have to go to an inverted V...100 degrees...and a 55-60 foot height, legs about 14 feet. I will let ya know if it woks...it should???
thanks
JohnB
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