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Author Topic: Vertical-Dipole Feed Line(s)?  (Read 5904 times)
K7RNO
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Posts: 279




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« on: July 18, 2013, 12:25:06 PM »

After overcoming some of my option paralysis...

1. One of my plans is to build a multi-band half-wave vertical dipole (MHVD). I am thinking of the ZS6BKW version of the G5RV. 93.8' long/tall, with 39.6' of 450 ohm ladder line.

As I understand from the ARRL Antenna Book, I need to run the feed line horizontal for quite a bit (there is no answer on how far), which I think I can manage somehow with a sky hook.

My main problem at the moment is the fact that I cannot reach my rig (with ATU) with just the ladder line because of the geometry of it all, and that I have to extend the feed line with coax. From literature I learned that I should have a tuner at the end of the ladder line, which is not feasible. What can I do to give this a chance of working at its best?

2. A second option would be a dedicated HVD for 20m, with an all-coax feed line. I will again be able to run that horizontal for a bit and then down to the ATU/rig. Will I need (or should I have) any kind of matching network with this kind of setup? What precisely? I do not have any measuring instruments available other than what my KX3 offers.

From previous study of this forum I also learned that I may be getting all kinds of answers, from no balun to this balun to a unun to nothing...and they cannot all be right. So, what will it really be?

Thank you for your expert, confirmed, proven advice (and as much supporting info to it as you can give)  Smiley

73,
Arno
« Last Edit: July 18, 2013, 12:28:53 PM by K7RNO » Logged

73,
aRNO
NAQCC #6870, SKCC #11131
WX7G
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Posts: 6136




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« Reply #1 on: July 18, 2013, 01:02:25 PM »

If you have the height for a 93.8' vertical dipole you have the height to mount the same antenna as an inverted vee. The inverted-vee will work much better for two reasons:

1. The vertical dipole will exhibit high angle lobes above 14 MHz
2. The vertical dipole vertically polarized signal will experience higher ground loss in the far field (10 dB vs almost 0 dB). I can check this with EZNEC.

The one advantage to the vertical configuration is an omni-directional azimuth pattern (no nulls as the inverted-vee has).

The recommended distance for bringing the feedline away a right angles from a dipole is 1/2 wavelength. The cost of not doing this is radiation pattern skew, which isn't the end of the world. This can be modeled with NEC.  

You might consider a multiband trap dipole such as the Hy-Gain DP-5BDQ fed with coaxial cable. Note that this is not designed for the WARC bands but will work then using a tuner.
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WB6BYU
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Posts: 13342




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« Reply #2 on: July 18, 2013, 01:33:08 PM »

Quote from: K7RNO

1. One of my plans[/b] is to build a multi-band half-wave vertical dipole (MHVD). I am thinking of the ZS6BKW version of the G5RV. 93.8' long/tall, with 39.6' of 450 ohm ladder line.



Probably not the best antenna choice for a vertical dipole because maximum radiation
is not perpendicular to the wire on 20m and higher frequencies.  You don't want it to be any
longer than an Extended Double-Zepp (2 x 5/8 wave) on the highest frequency where you
want reasonable performance.  (And probably not less than  1/4 on the lowest frequency
to maintain efficiency, which sets a practical limit of about 2.5 : 1 on the frequency range
of any such antenna.)



Quote

My main problem at the moment is the fact that I cannot reach my rig (with ATU) with just the ladder line because of the geometry of it all, and that I have to extend the feed line with coax. From literature I learned that I should have a tuner at the end of the ladder line, which is not feasible. What can I do to give this a chance of working at its best?



The ZS6BKW is designed to be fed with coax to the specified length of open wire line,
at least on the bands where it is supposed to work.  That's the whole reason for that
particular combination of antenna and feedline lengths.


Quote

2. A second option would be a dedicated HVD for 20m, with an all-coax feed line. ... Will I need (or should I have) any kind of matching network with this kind of setup?



A half wave dipole fed with coax cable shouldn't need any additional matching.  Just adjust
the wire length for minimum SWR in the middle of the operating band.



Quote

From previous study of this forum I also learned that I may be getting all kinds of answers, from no balun to this balun to a unun to nothing...and they cannot all be right. So, what will it really be?



One reason you get so many different answers is because, in practice, any problems from
not using a balun, or using the wrong type, are often not readily noticeable, or not of
concern to the operator.

In my experience, for somewhere around 75% of the dipoles put up without a balun the
operator doesn't notice any problems (at least not ones that they ascribe to the lack of
a balun.)  So, at least, one isn't necessary in the sense that antennas often work
well enough without one.  Among those installations, however, may be cases where
the operator complains about a high noise level, interference to the home alarm system,
or the SWR changes when they plug another cable into the unused port of a switch or
change the coax length.  All of those symptoms might be solved by using an appropriate
balun.

So good practice is to use a 1 : 1 balun, preferably of the current type (rather than a
"voltage" balun).  This may take the form of a choke balun, using either ferrite cores
(for wide bandwith) or coiled coax (which has a fairly narrow bandwidth over which it
is effective).  On the other hand, if you don't have a balun handy and want to get on
the air, there's a good chance that you can get it to work well enough without one in
many cases.
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K7RNO
Member

Posts: 279




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« Reply #3 on: July 18, 2013, 03:05:39 PM »

Well, I was asking for it, wasn't I! Let me regroup...  Undecided

But thank you for the responses so far! Aren't antennas fascinating?   
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73,
aRNO
NAQCC #6870, SKCC #11131
K3VAT
Member

Posts: 731




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« Reply #4 on: July 18, 2013, 03:17:09 PM »

One final item ... I didn't see what were your operating goals with this antenna.  Is it primarily for general multiband operation such as working mainly around USA including the ragchewing with the 'locals'; or specifically designed to work certain bands more frequently maybe to a certain part of the world; or is it for all-out DX'ing really wanting to maximize your potential to accumulate DXCC Entities??

Each of the three above options will dictate which antenna option(s) will best serve you.  As WX7G mention, if you have a single support of nearly 100 feet you're well on your way to have a large number of options available to you and the inverted vee is certainly an attractive antenna, especially constructed in a trap version which I successfully used for 5BDXCC.

GL, 73, Rich, K3VAT
« Last Edit: July 18, 2013, 03:19:21 PM by K3VAT » Logged
K7RNO
Member

Posts: 279




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« Reply #5 on: July 18, 2013, 03:23:01 PM »

Rich, thank you for that additional suggestion.

To be honest, I am dreaming of DX but am still learning my transceiver with its myriad of features, and dealing with the fact that the max power is 10W (for CW, fortunately).

If I had to select specific bands, it would be 20 and 40m at the moment. This may change with more experience...
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73,
aRNO
NAQCC #6870, SKCC #11131
WB6BYU
Member

Posts: 13342




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« Reply #6 on: July 18, 2013, 03:36:57 PM »

A half wave dipole for either band isn't a bad antenna, whether installed vertically or
horizontally at reasonable height.  Generally, horizontal and up high is likely to be
somewhat better for DX, depending on your local soil conditions.  (That certainly
wouldn't be the case if they were hanging over the Great Salt Lake, for example.)

For a wire vertical, a quarter wave ground plane with two elevated radials is easy to
build and should give a good match to 50 ohm coax without a tuner.

An excellent starting point is to put up either that or a horizontal dipole, then put up
the other and switch between them to see which works best for you.
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K3VAT
Member

Posts: 731




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« Reply #7 on: July 18, 2013, 03:46:53 PM »

...
To be honest, I am dreaming of DX but am still learning my transceiver with its myriad of features, and dealing with the fact that the max power is 10W (for CW, fortunately).  If I had to select specific bands, it would be 20 and 40m at the moment. This may change with more experience...

Many consider 20M and 40M to be the best pair of bands for DX operation throughout the crazy sunspot cycle.  Whether we're at solar max or solar min or somewhere in between, these two bands are often the most consistent & reliable offering up worldwide propagation and supporting transcontinental QSOs, even with 10 watts!  I'm constantly amazed at the new JT-modes on 20M where the majority of ops seems to be running 5 to 10 watts and working some nice long haul DX (I'm talking about VK/ZLs from here on the east coast), often with wire antennas.  I'm commonly on 40M at sunrise, then switching over to 20M till mid-morning, then back to 20M late in the afternoon, and finally 40M after dark.  [I do take a peek at 17M and 12M now and then as was the case last evening when 4U1ITU was on 17M RTTY.]

You might want to consider starting with a 2 or 3 band antenna.  IMHO using two pairs of Unadilla traps you can construct yourself a fine 3 band inverted vee.  Then as you become more familiar with how your radio works, work a few thousand contacts and define your operating goals better, you can expand your antenna farm (as Dale has just mentioned a minute before my posting!).

GL, 73, Rich, K3VAT
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K7RNO
Member

Posts: 279




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« Reply #8 on: July 18, 2013, 05:36:04 PM »

I am honored by the confidence you have in me. Not sure if I will live long enough to accomplish all that but I would sure enjoy the journey.

BTW, I forgot to mention that these tall trees I am talking about are not in my backyard but in local parks. I cannot do anything other from home than receive. And don't ask me why  Lips sealed
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73,
aRNO
NAQCC #6870, SKCC #11131
N4JTE
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Posts: 1158




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« Reply #9 on: July 18, 2013, 06:21:22 PM »

Okay so you have gotten answers from many of us for an antenna you will probaly never build, in some park??.
If you wanted a better RECEIVE antenna then ask that question my friend!
Maybe I misread your final comment, if so sorry.
Bob
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K7RNO
Member

Posts: 279




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« Reply #10 on: July 18, 2013, 06:42:45 PM »

Okay so you have gotten answers from many of us for an antenna you will probaly never build, in some park??.
If you wanted a better RECEIVE antenna then ask that question my friend!
Maybe I misread your final comment, if so sorry.
Bob

I don't know where I lost you, Bob, but I may have miscommunicated. Yes, I will build a new antenna to transmit from Utah Lake State Park.
For receive at home, I am taken care of, thank you.

Funny it is you who would ask  Grin

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73,
aRNO
NAQCC #6870, SKCC #11131
WB6BYU
Member

Posts: 13342




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« Reply #11 on: July 18, 2013, 08:55:08 PM »

The simplest approach is to build a dipole for one or both bands, then you can install it
horizontally, vertical, as a sloper or inverted vee, or however the available trees permit.
That gives you lots of opportunities to experiment.

Personally I've had good luck with dipoles for multiple bands on a common feedpoint, but
there are also several ways that you can make a single dipole work on both 20m and 40m,
including traps, manual disconnects, parallel feed, the ZS6BKW and/or G5RV, a doublet
fed with open wire line or twinlead, and some clever matching schemes.
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K5LXP
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Posts: 4507


WWW

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« Reply #12 on: July 19, 2013, 06:28:33 AM »

I think you're over analyzing this.  Coming up with a complicated and cumbersome antenna to deploy out in the field will not add any value to your operating.  When I operate while camping or hiking my antennas of choice are dipoles or end feds that I can launch into the trees quickly and don't have to mess around setting up or adjusting.  Compared to "gain" antennas like a G5RV, EDZ's or whatever, a dipole offers better omni coverage and you don't have to deal with a tuner.

As K3VAT offered, a simple 2 band trap or fan dipole and a hunk of coax is going to be a pretty good antenna.  If you're able to get it 100' up into the trees you'll have a better setup with that than most op's have at home.  To get much "better" than that will require a big step in effort and complexity which in your case I don't think is going to add a lot of value.


Mark K5LXP
Albuquerque, NM
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AC4RD
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Posts: 1235




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« Reply #13 on: July 19, 2013, 07:41:50 AM »

 I forgot to mention that these tall trees I am talking about are not in my backyard but in local parks.
[/quote]

Arno, I've got a suggestion, though it's a bit different from what you've heard so far.  I've done a lot of "back-yard portable" operating over the last few years.  Sometimes I'm using my existing HF antennas, sometimes I'm playing with new things--you were quite right when you said that experimenting with antennas is a world of fun.  Wink

I've had a lot of fun and worked a lot of DX with various homebrewed verticals, usually single-band, with elevated radials.  A few pieces of aluminum tubing from DX Engineering or your local hardware store can be turned into a vertical mounted on a tripod or fiberglass pole very easily.  Add 3-4 radials that you roll out when you set up the antenna, and roll back up when you're done, and you have the makings of a very good antenna!

And you CAN work DX with an antenna like that, I promise!  That ten watts of CW you mentioned is enough to work the world--and you'll have a bunch of fun doing it.  I think the single most fun I've had with radio in the last couple of years was working Australia on 5 watts, sitting outside with the dog and a barley-based beverage on a pretty spring evening. Smiley

There are probably a million plans for simple verticals on the web, but if you're interested and want specifics of my own portable temporary antennas, feel free to ping me off the forum.  73 GL!  --ken
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K7RNO
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Posts: 279




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« Reply #14 on: July 19, 2013, 09:03:16 AM »

If you're able to get it 100' up into the trees you'll have a better setup with that than most op's have at home. 

To utilize that branch 90' up in  the tree, I can only use a vertical antenna. At 90' up there I'd be in the thicket of all the other branches of the tree and cannot go horizontal or might not even get into an inverted V with an acceptable spread angle.

So, inverted V would have to be significantly lower, but I assume that would still be very good. A problem may be that I now need to spread out from there to the sides in order to meet the flat angle requirement and keep the ends sufficiently off the ground (in a public park). I might not have that real estate.

That, and the fact that an HVD shows to have a very favorable (i.e., low) radiation angle (see pp 2-11 and 9-10 of 22nd ed. Antenna Book), was what attracted me to that solution. BTW, being close to the lake, I would expect a high water table under the surface and therefore a very good ground. However, I am not sensing a lot of enthusiasm here and wonder why that is.

If you (you in general) now say "go ahead and try that HVD", then I am back to square one with my ingoing question on how to design the feed line: Ladder line > ? balun ? > coax > [ATU/TRX] ?

Of course, I could also use an existing MFJ 1979 1/4w whip for 20m, pull that up into the tree, add some elevated and sloping radials somehow and try that. That would be something inspired by Ken's post. Might it make a lot of sense?

Thank you again to all of you for being supportive and sharing your wealth of knowledge. It is highly appreciated and I am learning a lot.
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73,
aRNO
NAQCC #6870, SKCC #11131
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