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Author Topic: Home Brew Questiom  (Read 2931 times)
NI0Z
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« on: July 03, 2012, 01:59:49 PM »

This is just a theoretical question for which I assume the answer is it wont work because the wires would interfere with each other.

If I person took a bunch of PVC conduit and cut it to workable lengths for 40,30,20,17,15,12,10,6, and two meters and ran the wire for each band up it's respective tube and bound all the PVC pipes together to fashion a multi and vertical with radial plate and radials, would it make a better vertical than say a G5RV that uses one strand of wire to try and accomodate multiple bands?  

If one was only using one band at a time would the wires couple with each other and cause loss of resonance for any given wire?  I am thinking about how the multiband HeX beams work and wondering if a vertical could be created in a similar way and how much space between the wires would be needed?

Thanks in advance for entertaining this question!
« Last Edit: July 03, 2012, 02:11:32 PM by NI0Z » Logged

N2EY
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« Reply #1 on: July 03, 2012, 02:16:44 PM »

What you're describing is a vertical made from a bunch of parallel elements. Not a new idea - I built one from an article in a 1950s QST, and it wasn't a new idea then.

The main problem with parallel-element verticals and dipoles is that the elements interact. The closer they are, the worse the interaction. Which means you can have a real fun time trying to get them all adjusted correctly.

Doesn't mean it can't work. But unless you're very, very lucky, you won't be able to just cut the wires to formula length and have it work right on the first go.

---

Over the years I have found that amateur radio antennas involve no more than 10% electrical engineering and no less than 90% mechanical engineering. In many cases the ratio is more like 5%/95%.

What this means is that the major challenge is building the thing mechanically, not electrically. A quarter wave vertical for 40 meters is about 33 feet long - how will a 33 foot PVC pipe be fabricated and how well will it stand up? And that's just one problem!

73 de Jim, N2EY
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KQ6Q
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« Reply #2 on: July 03, 2012, 02:23:02 PM »

Actually, having PVC tubes of 1/4 wave bound together in a bundle is kind of a cool idea - the various lengths reinforce each other, so the length between the for 40 meters and the next longest, 30 meter section would be the only one unsupported. Use thicker wall tubing for the section for 40 meters. If you left the top ends uncapped, it could make a really cool sound when the wind blows! While this concept sounds like fun, a trap vertical would really be a lot more practical and less work!
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NI0Z
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« Reply #3 on: July 03, 2012, 02:46:24 PM »

I wouldn't actually use PVC, heheh, would look like and organ pipe antenna!

Actually I was sort of thinking about one tall mast and at the top having a plate like you see on some wind chimes and the wires would all hang down at their various lengths in a circle.  They would hang from string cut so they are all at proper height and feed to the bottom plate terminals which would have the connector and radial plate.

So, theoretically speaking they could hang around the mass on a circular plate almost like a radial plate to give them a little distance from each other.  The wires would have a plastic coat like they do on my hex to serve as minimal isolation.  Isolation would really be achieve by separation of distance.  There could be some guide plates down the pole which would also have guy holes to hold the mass up.  The wires/string could run through holes in the plate to help maintain separation in strong winds.

Thinking about it, one could even hang it from a tree by tossing up a rope over a branch like i do with a g5RV and hoisting this up in the trees and letting it hang.  Let gravity do the work and just secure it to a ground plate.

I was thinking quarter wave on all the long elements and maybe half and even full on the shorter ones.

So we would assume 33 foot mass for this design.  BTW, I have never made my own antenna yet, so I am newer than new to this and curious.  Not saying its practical.

Let's say we overcome coupling, would this perform better than the average vertical if a person got it all setup just right?



« Last Edit: July 03, 2012, 03:31:11 PM by NI0Z » Logged

K7KBN
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« Reply #4 on: July 03, 2012, 05:09:33 PM »

If you really want to know how well it will work, build it, test it (taking voluminous notes), and let us know!  You might come up with a nifty idea or two along the way.
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73
Pat K7KBN
CWO4 USNR Ret.
WB6BYU
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« Reply #5 on: July 03, 2012, 07:57:44 PM »

Quote from: NI0Z

I was thinking quarter wave on all the long elements and maybe half and even full on the shorter ones.



Not if you want a low SWR at the feedpoint.  Half and full wave elements have a high impedance,
roughly 2000 ohms or so.  That's not a good match to your coax.  If you want to use something
longer than 1/4 wave, the next step up is 3/4 wave.  (Though you may be able to use 5/8 wave
with a series loading coil at the base of each such wire before you connect them together at
the feedpoint.)



Quote

Let's say we overcome coupling, would this perform better than the average vertical if a person got it all setup just right?



It would perform about the same as any other quarter wave vertical.

One approach you could take would be to make the 40m element from aluminum tubing so it is
self-supporting, then add the top and center plates to hold the rest of the wires.

If you look at the Hy-Gain Hy-Tower Junior, it looks very similar to what you propose, though somewhat
complicated by trying to squeeze 80m on the same support.


But I wouldn't bother adding the 2m and 6m elements - they want more height above
ground.  It would help for talking around town on 10m as well, but it doesn't matter as
much for ionospheric propagation.
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K3GM
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« Reply #6 on: July 03, 2012, 08:14:50 PM »

I had a lot of fun some time ago with a 4 wire vertical. I got a handful of small diameter PVC "crosses" and a length of pipe and constructed a series of spreaders about 12" across, drilled a hole thru each end of the spreaders, and passed a wire cut for each band thru the holes. I spaced the spreaders vertically about 5' apart and used mason's twine to connect the shorter wires to the upper spreaders, so the finished antenna looked very similar to a cage dipole. The top was hung from a high tree limb.  Gathering the 4 wires just above the grass, I soldering them into an SO-239 bulkhead connector and fed them directly with RG-8 which was coiled with 8 turns right at the feedpoint.  I laid a couple dozen radial wires out on the grass.  At the time, it cost less than twenty-five bucks to construct.  Tuning was a bit tricky, and an antenna analyzer help a great deal.
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NI0Z
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« Reply #7 on: July 03, 2012, 08:15:09 PM »

Thanks for answering my questions!

I do plan on starting to dig into Antennas more.  I have a GAP vertical dipole and a G5RV both in the backyard and a hex on the roof.  The Vertical dipoles only offers me the advantage of having 40M and a small portion of 80.  The Hex is two full SUnits better on 20-10 so there is little point in keeping the vertical.  It's a nice vertical, so I'll sell it and then I will keep the G5RV for my second receiver antenna since I won't need to Xmit on it.  The G5RV receives pretty well, so not too much of a loss on the vertical.  I did hit Japan a few times with the vertical though.

I am just looking at options I can build that will beat my G5RV as a second Receive and possible Xmit.  The G5RV causes some nasty RFI on Xmit.

I am looking at helical loops as well.  K8NDS I think has some nice plans for a loop.  I think Antennas will be fun for me!

I don't have VHF or UHF on my base station yet, that's only mobile right now, hence my considerations for those as well.  I do have an a SWR analyzer as well, so I am equipped to play.
« Last Edit: July 03, 2012, 08:23:54 PM by NI0Z » Logged

K0ZN
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« Reply #8 on: July 03, 2012, 09:33:15 PM »


 Fun to see another ham getting addicted to antennas and experimenting with them !  It is a lot of fun and they all have
"personalities" to some degree. One of the things you will run into is that some antennas, while looking good, and theoretically good.... DON'T work
very well ! ....and the reverse....some rather ugly and seemingly compromised antennas (due to real estate limitiation, etc.) end up working
significantly better than they would be expected to. A pretty good rule of thumb: if build some antenna and it is working very well....that is lots of
good reports, you hear well, etc., DON'T try to "improve it" !  Murphy's Law seems to always get into that one!  If it ain't broke, don't fix it! Sometimes
that means living with a little more SWR than you would choose.

 Your idea of the multi wire vertical or fan dipole...same thing in a dipole has been around for years. It can be a very efficient antenna.

 I have played with these and the spread between the wires is a BIG deal.  Currently, my homebrew vertical is a homebrew vertical element ( aluminum
tubing) with a single 20 M trap in it. I have a single wire element for 17 M, which I stood off 8" from the "main" antenna with some home brew PVC spacers.
 When I added the 17 M (1/4 wave) of wire I had to make it longer than the theoretical formula showed.....apparently because I was getting capacitive
reactance from the "main" antenna, which kind of surprised me. I figured it would add inductive reactance on 17 M. You always learn something. The
17 M wire element comes off the base at a 45 deg. angle to the first stand off insulator, then vertically. Works very well and, again, somewhat to my
surprise, the SWR was very decent.....no need to trim it. The addition of the 17 M wire on the side had absolutely Zero impact on the 20/40 bands.
I suspect that is because of the 8" of separation..... just a guess.

Keep in mind, that if you have a bunch of 1/4 wave elements, all fed at the same point,
the feedpoint impedance, be it "good or bad", will not impact how well a full size 1/4 radiator works.  i.e. The antenna will radiate FINE.....you just may have
some swr to deal with via a Tuner. Personally, I would rather just stick a Tuner in line than spend hours "tweaking" a bunch of separate elements. Close DOES
count if you have a Tuner between the antenna and transmitter. The SWR would likely be low ( under 3 ) in the worst case, so kind of a non event unless
you just can't stand the thought of using a Tuner. Note that HyGain/MFJ makes a multi wire vertical and the wires on it are significantly stood off from the
main antenna pole element....   I am sure to avoid/reduce interaction.

73,  K0ZN
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G4AON
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« Reply #9 on: July 04, 2012, 12:26:35 AM »

All those bands with parallel wires will cause severe interaction. You can "mix" parallel wires on bands such as 40/20 and 20/10 without issue provided they are spaced apart by 6" or more. The closer the wires are spaced the more they interfere with each other. The higher frequency bands will not work well compared to a modest dipole at 30 foot or so, due to high take off angles.

By adding a trap or two in the parallel wires will give you 3 or 4 bands without too much trouble. There are some ideas and pictures on my web site at: www.astromag.co.uk/vertical/

A whole lot cheaper than buying a multi-band trap vertical.

73 Dave
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K3VAT
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« Reply #10 on: July 04, 2012, 05:18:25 AM »

All those bands with parallel wires will cause severe interaction. You can "mix" parallel wires on bands such as 40/20 and 20/10 without issue provided they are spaced apart by 6" or more. The closer the wires are spaced the more they interfere with each other. The higher frequency bands will not work well compared to a modest dipole at 30 foot or so, due to high take off angles.  By adding a trap or two in the parallel wires will give you 3 or 4 bands without too much trouble. There are some ideas and pictures on my web site at: www.astromag.co.uk/vertical/  A whole lot cheaper than buying a multi-band trap vertical.  73 Dave

Hi Dave,

I visited the webpage that you listed above (low cost fishing pole vertical) - IMO, the writeup is excellent and the photos are very informative - very well done!

I recommend that those interested in this topic (homebrew verticals) as well as parallel wire verticals & using traps in verticals & horizontals review and study this article.  It shows creative approaches involving inexpensive, homebrew materials to construct well-performing antennas.  I'm a big fan of use of traps and have used & currently use them in my dipoles.  Thanks Dave!

73, Rich, K3VAT
5BDXCC with wire
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KC4MOP
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« Reply #11 on: July 04, 2012, 05:30:25 AM »

I have pretty much solved my multiband problems. My A3S is dead in the water on a 60 foot pole I cannot access. The 40M option still works......strange.
I bought a JetStream JTV10 5/8 wave 10M vertical,,,,,,,,,,,nice!
I modified that monster HyGain 18HTJR to be just 40/15 Meters and ran a 5/8 wave wire 3 feet from the mast with PVC pipe for 17 Meters with an Ameritron antenna switch at the base. The 17M antenna has a separate feed line with a series coil to bring to resonance. 5/8 wave antennas are not resonant antennas BTW.
I have a full length dipole for 160M  and 80M @65 feet in the air fed by OWL for the lower bands. A good ole Dentron 3KA tuner in the shack.
Unfortunately this takes a little property to keep these antennas far enough from each other. But my problem is solved.

Fred
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K5KNE
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« Reply #12 on: July 04, 2012, 02:22:15 PM »

Don't make the problem harder than it really is. A resonant antenna on the working frequency or frequencies is best. A fan dipole (several wires for different bands) works O.K.
Your multi-band vertical is very similar, but you probably aren't going to get much return on your efforts.

Having every band may not be necessary either.  Put up a simple dipole for a band and try it.
Change it to be for another band and try that. Find the one you like best and use it.  Like you do with ice cream - you don't need to have every flavor they sell. Get the one you like and enjoy it.

Verticals offer some hidden challenges that simple dipoles don't. A friend once told me " A vertical antenna radiates equally poorly in all directions".  Without a very good ground radial system - this is very true.

Ham radio used to be an experimental hobby.  Today many hams are looking for a simple all band solution in their radios and antennas. Just try something, if it doesn't work - try something else something else.

73  Walter K5KNE
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KK4AXX
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« Reply #13 on: July 10, 2012, 12:02:41 PM »

A while back I built a 17M Vertical out of 3/4" & 1/2" copper pipe and a few fittings.  It works GREAT!  Then a friend gave me a 4BTV which I've 'rebuilt'.  The idea was to mount them to the same post and then feed both with the coax already feeding the 17.  Some said that it wouldn't work.  Others said it would.  A couple said to just give it a try.  I did & it works!  Yes, the addition did de-tune the great match on 17 a very little bit and I'm sure it isn't going to make my job any easier in getting all bands on the 4BTV functional, but none save 20M is too terribly far out and it will be worth the effort.

I don't have a clue about how hard it would be to tune all those bands, but what the heck, give it a try!
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