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Author Topic: 43ft multiband vertical  (Read 18430 times)
N2EY
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Posts: 3913




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« Reply #15 on: November 17, 2008, 08:31:52 AM »

ad4u WRITES: "What is the basis of the Love Affair some HAMs have with 43 foot verticals? Is 43 feet the magic length for verticals, or did the laws of physics change, or did advertising hype finally overcome all reason?"

43 feet is about 5/8 wave on 20 meters. That's the longest you can make a vertical before the pattern breaks up into lots of high-angle lobes.

---

I see several problems with the installation described.

First, on the bands above 20 meters (17, 15, 12, 10) the 43 footer is radiating a considerable amount of RF at high angles, where it is pretty much wasted.

Second, on the bands below 20 meters, its base impedance is low and reactive, and made even worse by the 4:1 "balun" (which should really be an unun).

Third, the SWR on the coax and the operation of the "balun" into a reactive load increase the losses.

--

IMHO, a 43 foot vertical can be a good DX antenna for 20, 30, 40, and 80/75 meters. Maybe even 160. IF all of the following conditions are met:

1) Good ground system (lots of radials)

2) Not installed near RF-absorbers like buildings full of structural steel, plumbing, wiring, ductwork and metal siding.

3) A low-loss matching network is installed *at the base of the antenna (the feedpoint)* and adjusted for each band.

73 de Jim, N2EY
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W5DXP
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« Reply #16 on: November 17, 2008, 09:47:01 AM »

> ES1TU wrote: What am I doing wrong?

I'm confused about using a 4:1 BALUN (BALanced to UNbalanced) device between unbalanced coax and an unbalanced monopole with radials. If your radial system is tied to your coax braid, that will short out one of your 4:1 BALUN windings. Or did you mean to say "4:1 UNUN"?

Without the balun, the SWR on the coax would be about 10:1. You might try the antenna without the BALUN if your autotuner will achieve a match.
--
73, Cecil, w5dxp.com
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W5DXP
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« Reply #17 on: November 17, 2008, 11:15:39 AM »

>  K0OD wrote: Yep, high dipoles are very effective but they have nulls: Bad on transmit but can be useful on receive. Best to be able two select between two dipoles in different directions.

My 20m rotatable dipole doesn't have any nulls. :-)
--
73, Cecil, w5dxp.com
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WA1RNE
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« Reply #18 on: November 17, 2008, 11:38:33 AM »


 Taking 80 meters as an example, a 43 foot vertical presents a horrible feed impedance for a 4:1 balun and 50 ohm feedline - around 10 -j300 ohms, a predominantly reactive load.

 It's been stated numerous times on this and other forums: baluns are designed to work with resistive loads that are a match for their design impedance.

 Not to imply that you believe this, but baluns are not designed as "magic" impedance matching devices that somehow automatically compensate for reactive loads. Unfortunately, baluns are being misused this way in some applications which at the end of the day, amounts to a lot of frustration to the user who, like yourself is trying to figure out why they can't obtain a decent match to a transmission line and the antenna isn't working to expectations.

 
 Assuming the radials are sufficiently long for 80 meters, I would chuck the 4:1 balun and feed this antenna at the base with either an autotuner or a manually tuned network.


 ...WA1RNE
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K6GC
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« Reply #19 on: November 17, 2008, 01:37:13 PM »

A 5/8 wave vertical will produce the lowest angles of radiation and strongest ground wave.  This is why Class 1A clear channel AM Broadcast stations have specified 100 degrees of electrical length (height) for many years.

As a dipole goes higher, it produces more low angle radiation.

Sooooo.....

How high and how long can you build your dipole ?

On some band it will almost certainly be less than 1/2 wave high, and on that band going down to 160 meters a vertical is a valid consideration you may wish to apply.

That being said, there are verticals and ground planes.  Even if you can only get your radials up 10' - high enough that people don't hit their heads when they walk under them,  The ground plane will almost always outperform a ground mounted vertical.  There are several reasons for this I won't go into here.

At my QTH I was able to get my dipole up 45' and so I have invested in a vertical for 160 80 & 40 meters.  When I lived in Santa Rosa it was on my roof for an unobstructed view at the horizon and it was an absolutely dynamite antenna compared to my dipole on 40 80 and 160.

Of course, my dipole is not very high and I don't have a beam.  So "dynamite" is an easy achievment.

Now then I just want to say one more thing that is slightly off topic.  Your super duper 100dB beam that squirts that lovely RF out in a half power beamwidth the size of a pencil has a pattern shaped like a tear drop.  That's because as the signal approaches the antipode all angles point to the target.  Often for this reason a vertical with 0dB can outperform the finest beams in this one particular application.  I have heard it argued that more than 10dB in a beam is getting close to all the gain that is useful.  I won't go into this except to say, "look it up."

TR, WB6TMY
http://www.radions.net/spamfltr.htm
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VK1OD
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« Reply #20 on: November 17, 2008, 01:54:47 PM »


ES1TU,

You have mentioned a 4:1 balun, but what type of balun is it? Is it a current balun or a voltage balun?

If it is a voltage balun, can you explain what it is doing?

Owen
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N2EY
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« Reply #21 on: November 17, 2008, 02:19:53 PM »

WA1RNE writes: "Taking 80 meters as an example, a 43 foot vertical presents a horrible feed impedance for a 4:1 balun and 50 ohm feedline - around 10 -j300 ohms, a predominantly reactive load.

It's been stated numerous times on this and other forums: baluns are designed to work with resistive loads that are a match for their design impedance.

Not to imply that you believe this, but baluns are not designed as "magic" impedance matching devices that somehow automatically compensate for reactive loads."

So true it bears repeating.

And even if the "balun" were a magic device that would do a 4:1 transformation and somehow eliminate the huge reactive part, the result on 80 would be to transform that 10-j300 ohms to 2.5 ohms. That's a 20:1 mismatch to 50 ohm coax - at the load end.

I suspect that most of the other bands would be equally poor matches.

Where a 4:1 UNUN would work is 20 meters - if a suitable capacitor were put in series with the antenna to cancel out the antenna reactance - because the resistive part of the feedpoint Z on 20 is about 200 ohms.

WA1RNE: "Unfortunately, baluns are being misused this way in some applications which at the end of the day, amounts to a lot of frustration to the user who, like yourself is trying to figure out why they can't obtain a decent match to a transmission line and the antenna isn't working to expectations."

There's also the point made by W5DXP that depending on the balun and its connections, one of the windings may be being shorted out.

WA1RNE: "Assuming the radials are sufficiently long for 80 meters, I would chuck the 4:1 balun and feed this antenna at the base with either an autotuner or a manually tuned network."

I agree 100%. Such an antenna should work very well on 80/75, 40, 30 and 20 meters.

73 de Jim, N2EY
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W8JI
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« Reply #22 on: November 17, 2008, 04:26:15 PM »

Let me try to work some sense into this barrage of information.

The vertical you have is critical for the type of balun you use. You either need a good current balun, or you need a modified voltage balun. You can NOT use a regular voltage balun or most of your power will excite the shield of the coax.

Let me explain why......

A regular voltage balun has the shield connected to a center tap on a bifilar winding. If you ground one of the output terminals and tie the other to the vertical, you run a 50/50 chance of doing one of two things:

1.) You will connect the center conductor of the coax directly to earth at the antenna, and this will excite the cable shield. the vertyical will be tied to the other hot flying lead of the balun, but there won't be much voltage there.

2.) You will, if it is reversed, tie the center of the coax directly to the vertical BUT the winding going to ground will be parallel to the feedpoint and trying to excite the shield of the coax and ground.

This is why you cannot use a voltage balun.

If you change the voltage balun wiring so it is an UN UN, by grounding one flying lead of the winding, connecting the other to the vertical, and connecting the coax center to the center tap, then it will work. The shield of the cable has to be grounded.

Now here is an additional problem. The feedpoint has a high impedance and is mostly reactive an most bands. This means you do not want a core like most real good baluns use. You want a core that handles high flux levels without losses. That would be perhaps a 43 material all the way down to a ui 10 iron core. It would have to tolerate very high flux density. You want a very low loss tangent at 30 MHz and lower.

This is NOT the tyoe of core you usually find in baluns built to be good baluns for specific impedances.

Secondly, it is a fact that a 43 foot vertical is no magic. Even AM broadcast stations avoid 5/8th wave verticals (225 degree). Instead they stay down around 100-120 degrees (below 3/8th wave).  There is a myth that 5/8th wave has gain, but Fresnel losses in the earth offset any gain. This does not mean on 20 meters the vertical won't work, it does mean you would probably be much better with a trap antenna that is 1/4 wave long or something 1/2 wave or less.

In the USA, BC stations stopped installing 5/8th wave verticals back in the 30's because of fringe coverage problems. You will still have the Fresnel losses of any vertical at HF.

Finally, you will have feedline losses in the system that are significant on 80 meters. The antenna should work OK but it would not be near as good as if you matched it at the base. It should be OK on 40 meters however.

None of what I am saying means your vertical will not work or make you happy, but something is clearly wrong with what you have now. I suspect it is in the balun since these antennas are critical for what you use. If you have a really good current balun it would be OK, but you would be better off with an UN UN that is designed to handle very high reactance.

You can NOT use a current balun unless you modify it into an un un. Again the core type is also a bit different because of the high reactance.

It will work.

By the way, never trust e-Ham reviews for critical information. They are mostly worthless for really learning how things work, like eBay feedback is. :-)

73 Tom











 
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K9WJL
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Posts: 183




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« Reply #23 on: November 17, 2008, 04:50:25 PM »

I've got a set up similar to yours. I've added about 50-55 new entities with this antenna.
 Know this, The guys preceeding my response are correct, The antenna isn't resonant or efficient anywhere. The 6m- 160m advertisement IS BS. I have a world class VHF contester living about 150 miles away from me, and he couldn't hear this thing on 6m.
 BUT, If you want an antenna you can use in a limited space, dosen't look like an oil well or a funky aluminum cactus and you don't mind putting down alot of radials, The Zero-Five is a pretty good antenna on 17, 20 and 40 meters.
 Here in Illinois, I don't have the coastal location alot of others have or the beams, but sometimes I really am first call in the pileups but sometimes I call my fool head off and never have them come back to me at all.
 Best thing you can do, is dont follow Zero Five's advice about the Coax Tied into the Radial Plate.
 I took A/B field strength measurements, and my radiated signal DOUBLED after tying into the Plate. I have run 1500 watts into the system without any failure at all.
 Also, get yourself an amplifier and a tuner and be patient. The sunspots are coming.
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K0OD
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« Reply #24 on: November 17, 2008, 05:39:14 PM »

W8JI says: "Even AM broadcast stations avoid 5/8th wave verticals (225 degree). Instead they stay down around 100-120 degrees (below 3/8th wave). There is a myth that 5/8th wave has gain, but Fresnel losses in the earth offset any gain."


Tom, why do commercial AM stations use verticals slightly longer than 1/4 wave? Should hams be building 100-120 degree verticals?

Heard a ham last night raving about "the gain" of 5/8 wave verticals. Of course he didn't have one. My experience with two 5/8 wave verticals on 20 is that both were mediocre DX performers and terrible close-in.  
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NA0AA
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« Reply #25 on: November 17, 2008, 06:03:07 PM »

I don't have the 43' vertical, although I am considering one for installation at a part-time QTH where dipole supports are not very good and a single stick, if painted, would be very easy to conceal.

I'm told that 41' is actually a better length, electrically.

What I do have is a 31' tall stick, which is a 12 ga wire inside an MFJ fiberglass fishing pole, fed at the base with an SGC SG-230 antenna coupler and a few radials [not enough and not radial enough, but this thing sits on my property line....].

I compare this to my a fan dipole for 80/40 at about 35', a 20 meter dipole at about 20', a 10 meter dipole at 20'

the vertical is almost always a better antenna on 20 and up, and sometimes on 40 depending on the skip.  

The vertical is deaf on 80 compared to the dipole.

I want to suggest using an antenna coupler at the base of the vertical rather than a balun with a tuner in the shack - MFJ makes two models suitable for this, besides the SGC units.  I'm sure that a clever fellow could easily whomp up a manual or remote tune coupler as well if you had a well stocked junk box.

The only downside is that the couplers are not rated for power - one SGC is good for 500 watts SSB but it's more than a grand!

The advantage is that you have a good match on your transmission line.
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WB6BYU
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« Reply #26 on: November 17, 2008, 09:23:13 PM »

In addition to the balun problem that Tom mentioned, you also have to
remember that the performance of a vertical at low radiation angles
is highly dependent on the ground conditions out to 100 wavelengths
or more from your antenna.  Since most hams are not going to lay out
enough 5 to 10km radial wires to make a difference, there is nothing
practically that you can do about this.  It means that a vertical antenna
that works very well in one location may not work nearly as well in
another.

By contrast, horizontal antennas are more predictable because the
phase shift and amplitude of the ground reflections change less with
soil characteristics.   Over poor soil a low dipole will work relatively
better than a vertical compared to very good soil, and it isn't uncommon
to find that a dipole or inverted vee supported by the top of the vertical
will actually do better.  But that is highly specific to your own soil
conditions and not the design of the antenna.
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VK1OD
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« Reply #27 on: November 17, 2008, 09:58:56 PM »


I asked the question about the balun type, and no information seems to be forthcoming.

Many people have modelled and waxed on in previous threads by this OP, but I didn't see any discussion about the balun type.

My view is that a voltage balun will have undesirable side effects of driving the outside of the coax from the antenna base.

My view of an effective current balun is that it will not drive the coax outer, but depending on the load impedance, may be lossy.

My guess for the motivation for the balun is a similar commercial product that uses a 4:1 balun, though the online product documentation does not identify whether the balun is a current balun or a voltage balun.

Owen
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ES1TU
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« Reply #28 on: November 18, 2008, 01:33:40 AM »

vk1od, w8ji:

I dont know if it's a current or voltage balun (I believe that I will gain lots of experience and knowledge in months to come). The balun came along with the vertical itself. I will open the balun box and make some pictures of my installation tomorrow morning (local time).

ES1TU
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W8JI
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« Reply #29 on: November 18, 2008, 06:08:01 AM »

I think from reading all your posts you have a Zero five vertical. I would think that vertical comes with an acceptable balun. Maybe it does not.

VK1OD has something about losses on his site:

http://www.vk1od.net/multibandunloadedvertical/index.htm

I haven't read the instructions but someone said the instructions have the coax shield floating. I wouldn't know why!!

73 Tom

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