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Author Topic: 40M vertical wire  (Read 2652 times)
KA1J
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Posts: 168




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« on: April 02, 2013, 02:34:23 PM »

Looking for a better option than a 40M quarter wave vertical wire for 40M & 15M.

My antennae are constructed of CAT cable. I have 60 radials 130' long on a salt marsh, 350' of coax running to an Ameritron remote coax switch which lets me select a 130' inverted L, a 66' inverted L. a 33' vertical, a 30M 1/4 wave (don't recall the length) and a butternut HF9V in the middle of the radial plate. With this arrangement I do not need a tuner and just switch to whichever antenna fits the band I'm on. All the wires are mostly vertical and held up by ropes strung up over the tree tops.

the 130' Inv-L works on 10M, 15M, 12M and 160M,
the 66' Inv-L works on 12M, 17M and 80M
The 40M works on 15M & 40M
The 30M 1/4 wave only works on 30M
The Butternut works on all but 160M

The 33' (40M) antenna came down in the snow and I've been using the butternut but it's not as good as the 33' vertical on either 40M or 15M, the 160 Inv-L works better on 15M than the Butternut does.

Here's the question, using the radial plate that I have, is there another length I might consider for 40M that will also work well on 15M? The 80M ant gives me a 1:2.7 SWR on 15M and 1:4.2 on 40M. The 80M Inv-L gives me 1:4.1 SWR on 40M so I can't use that though I get a 1:2 SWR on 15M.  The only wire antenna I have for 40 that has a nice SWR is the 33' one that I need to replace.

I don't have an antenna modelling program to try different lengths of an end fed wire that is ground mounted for 40 & 15M that will be OK without a tuner.

Suggestions?

Thanks,

Gary
KA1J
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WB6BYU
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Posts: 13028




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« Reply #1 on: April 02, 2013, 05:19:21 PM »

Your SWR numbers will be easier to follow if you put them in the right
order:  it is always expressed as a ratio to 1.  So 2.4 : 1 rather than
1 : 2.4.


You can't do much better than a quarter wave, around 33'.  Adjust the
length for resonance in your favorite part of the band.

The 15m resonance may be a bit high, however.  That can be solved by
adding a "capacitance hat" of some sort about 12' up the wire.  Could
just be a stiff wire sticking out on two sides, or a Vee-shaped bent
piece of wire with both ends attached to the main wire.  Either should
be able to add enough capacitance to lower the 15m resonant
frequency without affecting the 40m resonance too much.


There are other lengths you could try for 40m, especially with the
addition of some matching components at the feedpoint, but with 3/4
wavelength on 15m the wire is already a bit long for good performance
on that band.  For that reason I wouldn't go any longer if you want to
use it on 15m.


My main concern about your numbers was how GOOD the SWR is on 40m
using the 80m inverted L.  I would expect a feedpoint impedance over
1000 ohms, for an SWR > 20 : 1.  The fact that it is lower would suggest
that the cable is lossy.  But when I use VK1OD's calculator for 2000
ohms through 350' of RG-213 on 40m, I get about 4.3 : 1 at the shack
end of the coax (and about 10% efficiency due to the high SWR) so that
actually is about right.

Shows that, just because a tuner can match it, it doesn't mean that the
antenna is very efficient!

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KB4QAA
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Posts: 2269




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« Reply #2 on: April 02, 2013, 05:21:47 PM »

There are only a few choices, which should be obvious and they are the related harmonics lengths.   1/8, 1/2, 5/8, 3/4.  of 40m.

You don't say why you won't just replace the fallen antenna. but from the above choices 1/8wl would be the easiest to install.  

Congratulation on your antenna farm it's definitely one to be proud of!

p.s.  You have have made a very simple question confusing by including so much extraneous information. Wink
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KA1J
Member

Posts: 168




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« Reply #3 on: April 02, 2013, 07:38:59 PM »

@ WB6BYU

"My main concern about your numbers was how GOOD the SWR is on 40m
using the 80m inverted L.  I would expect a feedpoint impedance over
1000 ohms, for an SWR > 20 : 1.  The fact that it is lower would suggest
that the cable is lossy.  But when I use VK1OD's calculator for 2000
ohms through 350' of RG-213 on 40m, I get about 4.3 : 1 at the shack
end of the coax (and about 10% efficiency due to the high SWR) so that
actually is about right."

I can't use the 80M Inv-L for 40M, the SWR is 4.2. I don't have a tuner in line, I have two tuners but prefer to have resonant antennas rather than use a tuner at the shack to satisfy the rig but suffer great losses because of the mismatch. A tuner at the feedpoint would be excellent. Thanks for the idea of a bit of capacatence 12' up. I can try that but I'll need to use different wire, I'm using 8 strand CAT wire for everything. Something to try! The match on 15 is pretty good with the 40M vertical, I don't recall the 15M SWR using the 40M antenna but around 1.8 sounds right

@ KB4QAA

"There are only a few choices, which should be obvious and they are the related harmonics lengths.   1/8, 1/2, 5/8, 3/4.  of 40m.
You don't say why you won't just replace the fallen antenna. but from the above choices 1/8wl would be the easiest to install. 
Congratulation on your antenna farm it's definitely one to be proud of!
p.s.  You have have made a very simple question confusing by including so much extraneous information. "

Nothing simple is ever hard, it just seems that way. I was thinking about 5/8 but don't know how that would fly on 15M. That's part of what I hope the feedback here will answer to. I can just replace the antenna, I'll need to fire the spud gun over a new tree branch anyway, the old one came down over the winter. It strikes me that since I have to go through the effort, I have enough vertical real estate that to use something ground mounted for 40M that has gain over a 1/4 wave vertical wire would be worthwhile if it still allows me to use 15M. One of the advantages of having two or more antenna that are resonant on a given band is a small difference in directivity and switching to see which is loudest is a nice advantage over a single wire.

Thanks for the congrats on the antenna farm, I can't put up a tower and this seemed like the most efficient way to cover all the bands, especially 160M and do so with better signals than with the Butternut (which is a good antenna & I was able to get VK9CZ with it). As to the Extraneous information, perhaps the answer to the question is in knowing what I have & the values involved may relate to the data I supplied. I'm not an antenna whiz but sometimes the obscure is the area where the answer lies. It never hurts to ask.

Thanks for the replies!
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WB6BYU
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Posts: 13028




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« Reply #4 on: April 02, 2013, 09:34:54 PM »

I don't know what you are using for coax, but with 350' of RG-213 on
15m the SWR won't be any worse than 3 : 1 regardless of what you
connect to the far end - even open or shorted.  The coax loss in that
case is around 50% (though you might be using a lower loss coax.)

As you get much above 5/8 wave the performance will drop off on 15m
(that's about 29').  It doesn't fall off so fast, however, that even the
standard 43' verticals are still only about 1dB down on 15m.  For 40m
operation you can make it longer - there 5/8 wave is 90' or so.  But
such lengths don't match 50 ohm coax unless you provide some sort
of matching network for it.  The only reasonable lengths that are going
to give a low SWR without additional matching are 1/4 and 3/4 wave.

If you want to experiment you could try a 3/4 wave wire for 40m with
a 15m 1/4 wave wire connected in parallel at the base:  that allows
you to vary the designs for each band. 

If you want to try a 5/8 wave antenna on 40m, try 82' with a 18uH
coil in series at the base and a 4 : 1 step-down autotransformer (UN-UN)
(adjust the coil to move the SWR curve across the band, and vary the
length of the wire to fine tune the SWR at resonance.)  The SWR on
that antenna will be high enough on 15m that you can add a second
1/4 wave wire (or another 5/8 wave - try 27.5' with 5.5uH loading coil).
You still have only one feedline, but can optimize the antenna for
both bands at the same time, which you can't do as easily using a
single piece of wire.
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W5WSS
Member

Posts: 1652




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« Reply #5 on: April 03, 2013, 01:37:08 PM »

I did an experiment with two antenna wire lengths that originated at the auto tuner one was connected to the tuner port 1 and the other longer antenna wire was connected to port 2.
They were both pushing against a tuned elevated radial system, that originated and located at the tuner.
The antenna wire each were dc isolated relative to each other but RF isolation was difficult especially via the internal RF switching within tuner.
The tuner would tune and either antenna wire would radiate but high induced current and voltage appeared at the other port and just was not something I liked.
Instead I opted for a single antenna wire that I chose to limit to a range of 1/4 wave to 5/8 wave then operated against the tuned elevated radial system.
I made up three quick change antenna wires where each would be responsible for a segment of the entire Hf spectrum.
I used a hoist and was able to change them fast like 3 minutes.
I liked the quick change system and it worked as expected.
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KA1J
Member

Posts: 168




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« Reply #6 on: April 03, 2013, 03:52:08 PM »

Interesting answers & a nice discussion. I am not an authority on antennas at all but I do enjoy getting advice and playing around with them. I love DX but can't have a really nice antenna system so I make do with the best I can with wire antennas. Originally I had the butternut attached to the radial plate with 10 130 radials on the ground and it worked pretty well (now there are 60). I then thought to see what would happen if I attached the center of the coax to a 66' wire to see the difference on 80M and the difference was striking, much more bandwidth as I expected but much better Rx & Tx reports doing an A-B test back to back. I then tried seeing if any other bands worked on the 80M quarter and found 17M & 12M had an acceptable SWR and worked better than the butternut. That was when I had the idea that perhaps if I had discrete antennas hooked to the radial plate and switched them from an antenna switch 10' away & had a separate coax to each wire, it might work well. I'm sure there's some interaction between the elements as they all go upward, angling away from each other. When I was done, the only antenna that worked on 20M was the butternut and 30M also required its own wire.

This system enabled me to make 9 bands of DXCC but I still have a ways to go before Honor Roll so if I can improve on the existing wire system I'd like to do it. Since there is a downed 40M wire it's worth it to play around and see if I can get something up that will be better than the quarter & still work on 15. That 5/8 wave sounds interesting, I wonder what it would do to 15M? help or hurt?
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WN2C
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Posts: 429




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« Reply #7 on: April 03, 2013, 08:24:02 PM »

Gary, take a look at the H-Pole in the other thread.  It looks pretty interesting and may fit the bill for you.

Rick  wn2c - No antenna farm here
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WB3BEL
Member

Posts: 78




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« Reply #8 on: April 04, 2013, 06:35:37 AM »

Generally I don't like vertical antenna on the high bands like 15m.  For most people they are not as good an antenna as a horizontally polarized antenna up 1/2 wavelength.

But since you live at the salt marsh, I'd say you are probably the exception to the general rule.  What I would recommend is not using a low band antenna on a harmonic mode.  While it is fine for casual operating, and the VSWR might be low, often the pattern is poor for serious DXing.

So my first suggestion is to insert a high Q trap in a 40 or 80m wire vertical for the high band in which you have interest.  This is probably an easy reasonably low cost solution.

But what I would really recommend is a separate antenna for 15m if you can find the space.  But fortunately you don't need much space for a 15m vertical. 

What I would really recommend is a four square as close to the salt water as possible.  Sink pressure treated 4X4s at the four corners as a base and mount a crappie rod or bamboo pole on each 4X4.  Run a wire along the support.  It will only be a bit over 16ft tall.  8ft 4X4 with ~5 ft above ground + 11-12 ft fishrod It could be a few feet less if needed just use top loading.  This way you will get some gain and some directivity which can make all the difference if you have some trouble hearing due to QRN/QRM.  It might even make one of those LP+SP uber-rare DX CW 30+WPM multipath signals that are ringing like crazy become more decodeable.  Even a two element 15m vertical array would be obviously better than a single vertical or trying to make a 40m/15m combo compromise vertical.
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W5DXP
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Posts: 3546


WWW

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« Reply #9 on: April 04, 2013, 12:37:41 PM »

... often the pattern is poor for serious DXing.

Often true but one must remember that Louis Varney invented the G5RV specifically for the 20m cloverleaf pattern that a 1.5WL dipole exhibits which I found extremely useful for DX from AZ to Europe, Asia, South America, and New Zealand. Here's why:

http://www.midtel.net/~pmam/a20mh.gif
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73, Cecil, www.w5dxp.com
The purpose of an antenna tuner is to increase the current through the radiation resistance at the antenna to the maximum available magnitude resulting in a radiated power of I2(RRAD) from the antenna.
N4OGW
Member

Posts: 288




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« Reply #10 on: April 04, 2013, 01:07:46 PM »


What I would really recommend is a four square as close to the salt water as possible.  Sink pressure treated 4X4s at the four corners as a base and mount a crappie rod or bamboo pole on each 4X4.  Run a wire along the support.  It will only be a bit over 16ft tall.  8ft 4X4 with ~5 ft above ground + 11-12 ft fishrod It could be a few feet less if needed just use top loading.  This way you will get some gain and some directivity which can make all the difference if you have some trouble hearing due to QRN/QRM.  It might even make one of those LP+SP uber-rare DX CW 30+WPM multipath signals that are ringing like crazy become more decodeable.  Even a two element 15m vertical array would be obviously better than a single vertical or trying to make a 40m/15m combo compromise vertical.

Yes, if you really have a "salt marsh" at your qth, start building vertical arrays! They will work very well.

Tor
N4OGW
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WB3BEL
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Posts: 78




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« Reply #11 on: April 04, 2013, 01:18:17 PM »

Don't know what I was thinking...15m lambda/4 vertical is only a bit over 11 feet tall.  Guess I had 20m on the brain...

Still think that the 4sq would be a good bet for you though. 
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KA1J
Member

Posts: 168




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« Reply #12 on: April 04, 2013, 06:53:24 PM »

Oh yes, I do have a Salt Marsh in my back yard. The water was so high thanks to Hurricane Sandy I went to transmit and it appeared to be an open wire so in the middle of the storm (at night) I went out to see what came down and everything was under sea water. Everything except the remote coax switch box...

I need to keep it simple. My best placement is surrounded by "Phragmites" & although these are the invasive kind and not protected as a native species, I'm not wanting to put my antennas in a field of waving 12' high marsh growth. It's amazing how much static there is from dry growth waving in the breeze. So my antenna need to be in the forest next to the marsh.

A 4 square would probably be wonderful but that would require an additional 350' of control line to get to it or, a separate coax egress from the house and another coax & shorter control line to meet the 4 square. It isn't going to happen here so I need to act or get off the stick. I have temporarily put back the 1/4 wave but at this point am looking at a 5/.8 wave for 40. My only hold back is the question of how it will work on 15M. If... I had another switch position on the 5 coax switch I could make something dedicated to 15M but as it is, I need to get 20M and the only way is a separate antenna & right now I use the butternut solely for 20M. No option for a dedicated 15M antenna...

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WB3BEL
Member

Posts: 78




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« Reply #13 on: April 05, 2013, 06:30:25 AM »

So I am not very clear about what you are saying about placement of your antenna.  If you can put it right near the salt water.  For example within 10 or so meters. Then the vertical on the high bands like 15m might be your best bet.

If it is more than 50m from the salt water and is therefore above some sandy soil, then almost guaranteed, you will be hands down better with a horizontally polarized antenna.  Even a simple dipole up 30 ft or so will have much better signal broadside to the elements.  I think that a 40m 5/8 wave antenna will not be a good performer on 15m.

But you can put two vertical wires on a single feedpoint and share the ground plane similar in concept to half of a fan dipole.  This can work quite well and is what I use most of the time on 80(1/4wire)/160(Tee Vert) fed from one coax sharing the same ground plane.  There is no switch just the two wires joined at the coax feed. The interaction is very minor and can be tweaked by tuning element lengths during construction.  The interaction will be much greater for 40m/15m however.

I don't know if you saw the Garden Beam antenna in QST a month or two ago.  This is a vertically polarized Yagi antenna.  If you could put something like this near the water's edge it would really play for you.

I experimented with an antenna that had a similar vertical yagi concept.  It had no boom like the Garden Beam but rather was made of some crappie poles that were anchored by 5 gallon paint buckets full of sand with PVC pipe and PVC Cross sticking 3 feet out of the top.  In this way you could move the antenna direction by moving the director and reflector around the radius of the driven element which was fixed.  Each element used three wires on three crappie poles.  One for each vertical element and two each for the elevated ground which were set in in the PVC cross.  The element spacing was fixed by having a rope connecting each bucket to the driven element bucket PVC tubing so you could estimate the distance without needing to drag out a measuring tape. The crappie poles are lightweight and collapsible.  You could find bamboo probably cheaper.  I wanted this to be portable for seaside testing.  3 empty buckets (Sand or stones local to operating location,) + 9 crappie poles + some wire = cheap performance DX antenna at the oceanside.  You could use PVC sand spikes like used by surf fishermen, but I found the bucket easier to move in the dark.  It comes with convenient handle.

This would be simpler than the four square and eliminate the phasing box and cabling.  It would have higher gain but have the disadvantage that you might have to go outside in the mosquito cloud or pouring rain at midnight to move the paint buckets and point your antenna to work a rare one.

This paint bucket vertical Yagi works pretty well for the high bands, but becomes unmanageable for the lower bands as the counterweight needed grows and the elements become unwieldy or require quying against the wind.

A small 2 ele Yagi or Moxon beam on a push up pole mounted to your house might be the best trade off for the higher bands.
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WB6BYU
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« Reply #14 on: April 05, 2013, 08:07:16 AM »

You should be able to connect a 15m 1/4 wave wire in parallel with any of the
antennas.  Connect it to the same feedpoint, run the wire a foot or so from the
other wire (or run it up to a branch in a slightly different direction) and prune
the wire length for low SWR on 15m.  It shouldn't mess up the SWR on the lower
bands.  (You could even stick a coax "T" fitting in line and plug it into the coax
at some point if you don't want to disrupt the other feedpoints.)

That would allow you to focus on optimizing the 40m wire for 40m performance.
A vertical wire longer than 34' or so is NOT going to work as well on 15m because
it will have too much high-angle radiation.  If you want to use such a wire on both
bands you'll need to add a trap or some other form of decoupling to isolate the upper
section.
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