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Author Topic: Multiband vertical - wire or tube?  (Read 4173 times)
WK5H
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« on: October 14, 2010, 07:32:53 AM »

I've been scratching my head on this one.

I've seen a few 43' verticals, the majority of them being aluminum, and the reviews are decent on most.

There's one 43' vertical which is basically a fiberglass pole with the radiating element being a wire running through the middle, and the fiberglass pole is the support.

But, my question is this...

Radials and compromises completely aside, what's the performance difference going to be between a 43' wire and a 43' aluminum antenna?

I have though about running a 43' wire straight up, and using my 4:1 unun to make my own multiband vertical, but wasn't sure if I was missing something.
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N3OX
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« Reply #1 on: October 14, 2010, 09:01:01 AM »

If you're going to do 4:1 UNUN feed, the fatter tubing vertical will have less extreme variations in impedance, and it actually will make the system work better.  A #14 wire vertical is as high as 15:1 200 ohm SWR over some of the 5-30MHz range... a 1.5" uniform tubing vertical is better than 7:1 SWR with respect to 200 ohms.

In both cases, things get bad on 80 and 160.   

If you're thinking of a tree-suspended vertical, I would probably recommend that you build a fat cage of wires.  You could do the same thing around a fiberglass pole. 

I used a #14 wire vertical on a fiberglass pole once, but I used base matching networks.

http://www.n3ox.net/projects/lowbandvert/

I would recommend considering at least the 80m coil for your vertical... the 4:1 UNUN and coax with tuner in the shack causes much more serious losses in the coax than the mismatch does on other bands...
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Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WX7G
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« Reply #2 on: October 14, 2010, 09:10:42 AM »

N3OX is correct. The highest 200 ohm VSWR above the first resonant frequency is 50:1 for a #16 wire version and 25:1 for a 1.5" tubing version.
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K3AN
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« Reply #3 on: October 14, 2010, 09:33:21 AM »

If you just intend to run 100 Watts, consider tuning the vertical with a remote autotuner, installed at the base. You'll have low feedline SWR on all bands. SGC, MFJ and others make such tuners. However, autotuners rated for higher power are VERY expensive.
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WK5H
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« Reply #4 on: October 14, 2010, 11:09:52 AM »

Thanks for the responses!

I'm guessing that the more surface area of the tubing allows for more RF to be radiated than the #14 wire?

This just makes me wonder how the DX Engineering 43ft vertical is able to obtain 160M - 10M.....  I'm not saying it can't; there are some really positive reviews on the antenna.  Just trying to understand the reasons as to why it would work but a wire wouldn't.
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N7DM
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« Reply #5 on: October 14, 2010, 11:34:27 AM »

If you can fashion a 'spreader', top and bottom, and create TWO vertical wire elements [shorted together at the top and bottom], you will have [in effect] a Two Element Cage antenna. That means 'fatter'...which translates to ELECTRICALLY longer than the same length of Weeny Wire. I'm guessing something like a metal clothes hanger, top and bottom, would do the trick. My last venture in this area was a 80 meter vertical, mounted on one of my 60 foot PVC masts. I used two foot spreaders and had the pair of elements straddle a set of mast guys. The thing was 58 feet high, and bridged out at Zero Reactance {resonance} on the low end of 80. That is around NINE feet shorter than the Cook Book says.... due to the 'fat' effect.

dm
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WB6BYU
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« Reply #6 on: October 14, 2010, 12:16:07 PM »

Quote from: KC5DEB
I'm guessing that the more surface area of the tubing allows for more RF to be radiated than the #14 wire?

This just makes me wonder how the DX Engineering 43ft vertical is able to obtain 160M - 10M.....  I'm not saying it can't; there are some really positive reviews on the antenna.  Just trying to understand the reasons as to why it would work but a wire wouldn't.

No, a wire or a fat antenna will radiate the same amount of RF.

The difference, as N3OX pointed out, is that IF you are feeding the antenna through a 4 : 1 UN-UN and a length
of coax to a tuner in the shack, the SWR on the coax is lower on SOME bands because the fat antenna has
a lower impedance.  This reduces the coax losses somewhat (and might make the tuner more efficient, depending
on the coax length.)

If you put the tuner right at the antenna feedpoint there is little difference between the two antennas:  the
tubing will have a SLIGHTLY higher efficiency due to less conductor loss, but not enough to notice.


So, really, an end-fed wire will work just as well in many cases.  The practical difference has to do with
feedline losses rather than the antenna itself.

As far as working 80m or 160m when tuned remotely though a long length of coax, that should be attributed
more to Marketing than to Engineering anyway.  If you wind a loading coil at the base of the antenna to
provide a better match on 80m or 160m, a simple vertical wire will outperform the tubing antenna that is
relying on a tuner in the shack.


Why do they get such good reviews?  On one hand, they aren't a BAD antenna (though the losses can be
high, especially on 80 and 160m.)  And, if you look through the reviews, you'll find that many hams are not
very critical about the antennas they buy - they wouldn't want to admit that they bought a real stinker,
would they?  You'll see rave reviews for a number of antennas that are worse than a dipole, and often
much worse.  Just because it gets great reviews doesn't mean you can't do as well with a simple wire
hanging from a branch.
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N3OX
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« Reply #7 on: October 14, 2010, 12:22:42 PM »

I'm guessing that the more surface area of the tubing allows for more RF to be radiated than the #14 wire?

No, that's not it.  Both will radiate almost all of the power you apply to them just fine.  It's all a matter of how much power you lose in the coax because you're running it with a bad mismatch.   The fatter the vertical, the less the mismatch, and in almost all cases, the less the mismatch, the less the loss in the coax.  

All of these 43 foot verticals are a compromise for simplicity:  you can always make them a little bit better by moving the matching system out to the base... because a short vertical presents an exceptionally horrible mismatch, on 80 and 160m, you can make them 10-20dB better by using a good loading coil at the base.

On the higher bands, if your UNUN is a beefy design and you use a pretty short length of big coax, like RG-8 or LMR-400, you wouldn't gain that much... on some bands you might only get 1dB, on others maybe up to 5-6dB in bad cases (long coax, thin coax).  

On any band, the fatness of the vertical matters, but it's only because the worst-case mismatches with thin wire are going to be worse, and that causes more loss in your feedline.

Quote
This just makes me wonder how the DX Engineering 43ft vertical is able to obtain 160M - 10M.....  I'm not saying it can't; there are some really positive reviews on the antenna.  Just trying to understand the reasons as to why it would work but a wire wouldn't.

 The fact of the matter is, even with fat tubing a 43 foot vertical used on 80m with tuner in the shack is pretty bad and used on 160m it's terrible... but the thing you have to remember is that "bad" and "terrible" are with respect to a well designed antenna, and no one has that for comparison.

The antenna works great vs. NO antenna.

My location is good for working DX on 160m.  Signals from Europe and the Carribean and Africa tend to be good in here.  Over three seasons, I worked 116 countries with twenty-five watts effective radiated power.  I have a small backyard and a short vertical, and it only radiates about 25% of the power that a 1/4 wave vertical would.   For the first few years I was on 160m, I only had a barefoot rig.

So I was radiating 25W.  And I worked 160m DXCC.  I can also work anything East of the Missisippi on CW with 5W... that's 1.25W radiated... and I've even worked a handful of Europeans who have good ears using that whopping 1.25W radiated power.

If you buy a 43 foot vertical and have 18dB coax loss, but you use a 1500W amplifier, you'll be radiating 25W too.  If you live in Maryland or anywhere on the East Coast like I do, that will be more than enough radiated power to get a basic DXCC on 160m.  If you live in the Midwest where it's much tougher, maybe not, but it will still out-perform a lot of other antennas.

So having an antenna that "works" is really relative.  A lot of people wouldn't even dream of running barefoot on 160m, so the 43 footer + UNUN + legal limit amplifier does about the same on 160m as me running barefoot to a 60 foot vertical with loading coil and postage-stamp radial system.

My antenna is a full size quarter wave on 80m. I probably radiate close to 75W or so, losing a tad to the small radial system.  I've worked Japan, Micronesia, Western Australia on long path, Madagascar, etc. etc...  again, this is with a barefoot FT-857D.    

The fact of the matter is, a lot of people use really awful transmitting antennas on the low bands and make up for it with an amplifier.  There's not really anything wrong with that, but it seems real silly to me, because you can build all the matching system you need out of house wire or 1/4" copper tubing!!!!

By the way, there's another thing... if you've never tried a perfectly straight-up vertical on receive on 80/160, the results can be SHOCKINGLY good.   The reason for that is that the big, deep null overhead knocks down all the thunderstorms and loud people in the pileups.   And you don't need good efficiency for reception.. signals are enormously loud on 80/160.

They're so loud that if your antenna is GOOD it's a liability.  I ALWAYS, ALWAYS use attenuation and turn the RF gain down if I receive on my transmitting vertical.  Otherwise, my front end gets hammered and I can't hear anything.  If you have a cheaper radio and you don't know to turn on the attenuator and turn down the RF gain (and turn off the noise blanker!) on 80m and 160m, all that nasty coax loss could let you hear way better!

You put up a 43 foot vertical that radiates 1% of your applied power, it's going to be a DX machine compared to, say, a 30 foot high dipole.  You'll hear lots of stuff and you'll be able to squeak out enough radiation using your big amplifier to work much of it.
« Last Edit: October 14, 2010, 12:28:02 PM by Dan » Logged

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

Monkey/silicon cyborg, beeping at rocks since 1995.
KI4Z
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« Reply #8 on: October 14, 2010, 09:10:37 PM »

WOW!!  I had no idea that 160M had any DX capability.  All I ever noticed in the few times I listened on 160M was electric noise.  40M and higher were my bands of choice, although occasionally would get on 80 for some quick CW contest multipliers.  I'll definitely give 160M a chance after hearing N3OX's comments! 

'73  mark
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K3GM
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« Reply #9 on: October 15, 2010, 04:26:05 AM »

If you can fashion a 'spreader', top and bottom, and create TWO vertical wire elements [shorted together at the top and bottom], you will have [in effect] a Two Element Cage antenna. That means 'fatter'...which translates to ELECTRICALLY longer than the same length of Weeny Wire. I'm guessing something like a metal clothes hanger, top and bottom, would do the trick.........

You can make spreaders out of PVC "crosses" and a four pieces of pipe 8"-10" in length.  Some years ago. I fabricated a four band vertical in this fashion.  I used monofilament line to replace the shorter wires in order to join everything at the top.  Tuning is a bit tricky and it helps greatly to have an antenna analyzer.
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WW5AA
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« Reply #10 on: October 17, 2010, 04:30:26 AM »

"WOW!!  I had no idea that 160M had any DX capability.  All I ever noticed in the few times I listened on 160M was electric noise."

160M is a great DX band, but as with anything else you have to have a good antenna. With my simple doublet I work lots of DX. The key on 160M and 80M is a good RX antenna. It helps to use CW when band conditions are poor. The best part is that in most cases the poor ops and lids stay on the upper bands!

de Lindy
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W0BTU
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« Reply #11 on: October 17, 2010, 05:00:23 PM »

... By the way, there's another thing... if you've never tried a perfectly straight-up vertical on receive on 80/160, the results can be SHOCKINGLY good.   The reason for that is that the big, deep null overhead knocks down all the thunderstorms and loud people in the pileups.   And you don't need good efficiency for reception.. signals are enormously loud on 80/160.

They're so loud that if your antenna is GOOD it's a liability.  I ALWAYS, ALWAYS use attenuation and turn the RF gain down if I receive on my transmitting vertical.  Otherwise, my front end gets hammered and I can't hear anything.  If you have a cheaper radio and you don't know to turn on the attenuator and turn down the RF gain (and turn off the noise blanker!) on 80m and 160m, all that nasty coax loss could let you hear way better!

You put up a 43 foot vertical that radiates 1% of your applied power, it's going to be a DX machine compared to, say, a 30 foot high dipole.  You'll hear lots of stuff and you'll be able to squeak out enough radiation using your big amplifier to work much of it.

Hi Dan,

The vertical you're speaking of doesn't work better for RX on 160 than your flag, does it? I can see how you're saying that the vertical can reject high-angle signals. But I've compared verticals and Beverages at more than one station, and the vertical was not a good antenna for receiving, anytime. For transmitting, a vertical is a "DX machine", but not for receiving. What ought to be "shockingly good" is a separate RX antenna, and not a vertical.

I just looked at your aerial photo on your site. Any chance you can put that flag antenna on the other side of the house? It might be picking up unwanted signals and noise being re-radiated from that vertical, as close as it is.
« Last Edit: October 17, 2010, 05:08:32 PM by Mike Waters » Logged

N3OX
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« Reply #12 on: October 17, 2010, 08:01:28 PM »

The vertical you're speaking of doesn't work better for RX on 160 than your flag, does it?

Not usually, but every once and a while.  Usually they're close with the advantage to the flag.  A flag isn't actually predicted to be that much better than a vertical anyway... if you use the "receiving directivity factor" that W8JI uses to assess RX antennas, a flag is only a few dB better than a vertical when noise is uniformly distributed!  'Course out here on the East Coast, a lot of times I have to contend with storms and QRM from the continent when I'm trying to hear out over the ocean.  Then the flag is killer.  The noise is most definitely not distributed from every direction, and then my 20dB F/B helps.  

Quote
I can see how you're saying that the vertical can reject high-angle signals.

And that's the thing...the flag has a lot of high angle response coming from incomplete cancellation of the horizontal wires. I've been thinking of phasing a pair of short vertical dipoles  on a short boom to give me a "less high angle pickup" equivalent to the flag.  The flag just has worse elevation pattern, at least off the front and sides, than a vertical does.  So if there are thunderstorms, say, in the Carolinas, sometimes the vertical wins.    Not by much and usually on nights when I can't really hear anything anyway... but sometimes it matters.

Quote
But I've compared verticals and Beverages at more than one station, and the vertical was not a good antenna for receiving, anytime. For transmitting, a vertical is a "DX machine", but not for receiving.

I've tried to test as best I can here, listening in stereo on two rigs with the levels equalized, and then swapping rigs.  I don't have a phase-locked diversity RX or even identical radios... that's why I swapped RX's, to help control for that ...  I think I even tried swapping which ear I had on which antenna just in case I have a better DXing ear.  The flag is a little bit, but not a lot, better in those tests.  
'Course if I try to listen on the vertical without attenuating it 20dB or more, it tears apart my front end.  But it's not bad with heavy attenuation.

It takes some pretty critical listening to determine that the flag is really better.  It's never the case on a quiet night that I can hear things on the flag that I can't hear on the vertical... and honestly, if I found that, I'd think something was wrong just because the predicted advantage is subtle.  The advantage is there, but it's small on a quiet night.  On a noisy night when there are thunderstorms far enough off the back, it's no contest.  Sometimes I feel like the flag is a perfect shield of silence when I'm on 80m in the spring pointing toward EU or Africa.

Quote
I just looked at your aerial photo on your site. Any chance you can put that flag antenna on the other side of the house? It might be picking up unwanted signals and noise being re-radiated from that vertical, as close as it is.

I float my vertical when I'm receiving, so it's a floating eighth wavelength on 160 and a floating 1/4 wavelength on 80m.   That makes for very good decoupling.  I've checked it with and without detuning and I can toggle people off the back 10dB or more by switching the wire on and off the loading coil on 160...  you're right that keeping your TX antenna from re-radiating is critical. But that's fairly easy to do when you've only got 60 feet of conductor and can just lift it from ground.

Quote
What ought to be "shockingly good" is a separate RX antenna, and not a vertical.

I calculated the RDF at 10 degrees takeoff angle for a 60 foot vertical like mine vs. a 30 foot high 160m dipole.  The RDF of the vertical at 10 degrees elevation is about +3dB.  The RDF for the dipole is about  -6dB.    So there's a 9dB RDF advantage going from a low dipole to a vertical.  That's about the same improvement as the best and worst antennas on W8JI's RDF chart at http://www.w8ji.com/receiving.htm.  Tom's chart is calculated for 20 degrees... a 30 foot 160m dipole clocks in at just about 0dB for 20 degree RDF over medium earth in EZNEC, so the vertical is about 5dB better in that case.   K7TJR has an inverted vee in his comparison chart and the conclusion is similar... 0.6dB RDF for the inv. vee at 120 feet:

http://www.k7tjr.com/rx1comparison.htm

All the RDF calculations assume you don't have nearfield coupling with noisy junk, and I think it's probably going to be the case that it's hard to decouple a transmitting vertical from the house, etc ... but if you don't have decoupling issues, a single vertical isn't terrible, and you have to get pretty elaborate to get the same improvement over a vertical that you get from going from a dipole to a vertical.  A flag isn't nearly elaborate enough to get the same improvement again Grin  I'm glad I have it, and it works.  But it's a subtle improvement over the vertical if I do a really critical, level-equalized listening test.  The next planned antenna (pair of short vertical dipoles) should give me an extra 2dB, but it's a project for later... I think I need active dipoles.  

I think in a lot of situations a dedicated receiving antenna can be easier to decouple from house noise, which isn't captured by any discussion of directivity.   And antennas with deep nulls can be critical in the suburbs: in that case RDF doesn't mean much compared to null depth and steerability.  And, of course, my transmitting vertical basically kicks my receiver's teeth in... the internal attenuator is OK in a pinch but it helps if I use a little extra.  But if I hold all other variables constant, the flag seems to be a tad better, but not a lot better, which is pretty much what's predicted.

Good Beverages should be much less subtle...  
« Last Edit: October 17, 2010, 08:04:48 PM by Dan » Logged

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

Monkey/silicon cyborg, beeping at rocks since 1995.
W0BTU
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« Reply #13 on: October 17, 2010, 08:17:16 PM »

Very good, Dan!

Have you ever tried a K9AY loop? I haven't but from all I have read about it, it is superior to the flag and similar antennas.

An alternative would be a remote RX location. But you knew that. Smiley
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W0BTU
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« Reply #14 on: October 17, 2010, 08:43:17 PM »

... Good Beverages should be much less subtle...  

There you go! You said it! Beverages are very forgiving, and it has been said that "they want to work". I agree. It's pretty hard to put up a bad Beverage.

But other RX antennas work as well as, or better than, a Beverage, such as an array of short phased verticals or the K9AY loop. Of course, they are more complex, but they take up a heck of lot less room.
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