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Author Topic: Do parallel dipole antennas work?  (Read 4452 times)
KJ6TSX
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Posts: 116




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« on: May 18, 2012, 08:24:09 PM »

I am looking at a Alpha delta parallel dipole antenna to be used for 80 to 10 meters. This unit has parallel lines with coils on each end.
What makes this antenna attractive to me is that it's total length is 80 feet. I can string that from one end of the house to a pole on the back fence with the high point being 35 feet above ground. Would I be better off with this or a off center dipole with about 30 feet at 7 feet above the ground.
Below is  a link to the website of the parallel dipole antenna. http://www.alphadeltacom.com/pg1.html
Thanks
George
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KF6A
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Posts: 214




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« Reply #1 on: May 18, 2012, 10:11:44 PM »

Quote from: KJ6TSX
Do parallel dipole antennas work?
Yes, they work fine as a dipole, although I am not a big fan of fan dipoles because you can do better in the same space.
 
Quote
........What makes this antenna attractive to me is that it's total length is 80 feet. I can string that from one end of the house to a pole on the back fence with the high point being 35 feet above ground. Would I be better off with this or a off center dipole with about 30 feet at 7 feet above the ground........
Either would probably work fine for what they are. I would, however, choose a different route. I would go with a ladder line fed 88' doublet and on 40m and up it is an antenna with gain over a dipole. If 88 feet wont fit just dangle the last four feet down at the ends. Of course the caveat is that you have to use a tuner but I'm a believer that all hams should own a tuner of some kind. Here's an interesting read for you. http://www.users.on.net/~bcr/files/backyard%20wire%20antennaes.pdf
« Last Edit: May 18, 2012, 10:14:33 PM by KF6A » Logged
NK6Q
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« Reply #2 on: May 18, 2012, 10:43:56 PM »

Looks like Alpha-Delta's version of the W3DZZ antenna:

http://www.users.icscotland.net/~len.paget/GM0ONX%20trap%20dipole.pdf

Bill in Pasadena, NK6Q
(working on my own homebrew W3DZZ)
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WX7G
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« Reply #3 on: May 19, 2012, 01:57:43 AM »

The Alpha Delta will work fine. You might need to use the autotuner in your transceiver (if you have one) to use the antenna on all the bands it is designed for.
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K5LXP
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« Reply #4 on: May 19, 2012, 05:57:12 AM »

I am not a big fan of fan dipoles because you can do better in the same space.

What could be "better" if it's the same size? 
 
Quote
I would go with a ladder line fed 88' doublet and on 40m and up it is an antenna with gain over a dipole.

But with gain lobes also comes nulls.  If you can't turn it, your nulls (quite deep and numerous depending on the band), it would seem half wave radiators would be "better" than a single long one that has a few nominal gain lobes and deep nulls.

I can't disagree that an 88' doublet fed with balanced line and matched with a tuner wouldn't be a good choice for a lot of situations, but if I could hang a fan dipole and get better azimuthal coverage and not have to dork with a tuner on every QSY, hands down the fan dipole wins.


Mark K5LXP
Albuquerque, NM
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WB6BYU
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« Reply #5 on: May 19, 2012, 07:30:29 AM »

The higher antenna is likely to work best.

The only magic of the 88' length is that it is as long as you can go and still have
broadside radiation on 20m.  The pattern breaks into multiple lobes on the higher
bands.  As you make it shorter the 80m efficiency drops somewhat.  In most cases
you won't notice much practical difference between, say, 80' and 100', although
the former may be a bit harder to match on 80m, and the lobes and nulls on the
higher bands might point in different directions.

The Alpha-Delta appears to simply be a set of parallel dipoles with inductive
loading for the lowest band(s).  I built a similar set of wires for 40 / 80 / 160m.
They work fine, though the bandwidth will be narrow on the lowest band.  If built
for a lowest frequency of 80m, I'd add the 80m loading coil to the 20m wire rather
than the 40m wire - that gives more design flexibility.  This also allowed me to
make the whole antenna only as long as the 40m dipole legs.


Whether an all-band doublet feed with ladder line is a better choice than multiple
dipoles on a single feedpoint depends on your preferences.  The latter allows for
direct coax feed on all bands without needing a tuner.  The former doesn't require
any adjustment of the antenna during construction and will work over most of the
HF range with an appropriate tuner. 

There are some situations where the preference may be clear:  in an inverted
vee configuration, the individual dipoles may be better on the higher bands,
depending on the slope of the wires.

But in the end it really comes down to personal preference:  do you want to
spend time initially tuning the antenna for low SWR and not need a tuner, or put
up the antenna quickly and use the tuner each time you change bands?  I've
used both methods, and they both work.
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KJ6TSX
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« Reply #6 on: May 20, 2012, 07:34:21 PM »

Thanks for all the replies
I have been doing a lot of reading on antennas  Grin So I think what I am going to do is take down my ground plane antenna and install the Fan dipole. Currently my antenna mast is mounted to the side of my house with a support aprox 3 feet from the peak and on at the peak. I am using 1" water pipe for the mast, there is a 18 foot antenna on top of the mast. Been up all winter (No problems) I want to raise the mast to about 15 feet above the roof and make that the top on my fan dipole inverted V antenna. Now the question If I use water pipe that would weigh 32.5 LB not including the antenna wire. Do you think I can get away with lighter tubing such as 1 1/4 top fence rail? I would prefer not to guy this if possible. The wire element should act as a guy it will be anchored into the wind. No Ice here (California)
Here is a picture on my current setup... Yep that the Mrs. wondering what I am doing Now http://i1107.photobucket.com/albums/h396/gsalet/Antenna-house.jpg
Thanks
George
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KI4SDY
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« Reply #7 on: May 21, 2012, 05:43:26 AM »

If it was me, I would use lighter telescoping electrical conduit and go from the ground up for better stability. I would leave the vertical on top, then the dipole underneath with a switch box in the shack. That would give you the best of both worlds. You will notice that you can make more and better contacts switching back and forth. Aim the dipole broadside for the areas you want to contact most, like East/ West? The more antennas the better! Grin

You may get by with using the dipole as a guy in two directions, but I would at least cover the other two directions with guys as well. You can never tell when a wind storm may blow through!  Shocked
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KCJ9091
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« Reply #8 on: May 21, 2012, 06:04:36 AM »

I have a 20' section of top rail mounted a ground level with a house bracket at 8' with a A99 on it and another section ground mounted with a bracket at 10' with a 12' dual band fiberglass antenna on it.  Both sway in the wind a little but have survived light ice and 70 mph wind gust (not at the same time).
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KJ6TSX
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Posts: 116




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« Reply #9 on: May 23, 2012, 08:10:07 PM »

I called by local metal supplier and bought a piece of 1 1/4 stainless steel tubing .065 thick was sort of expensive but it was stronger and lighter than the same sized galvanized steel. Plus I live close to the ocean so steel rusts real quick. I am going to put the fan dipole up this weekend. I will let you know the results
George
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G4AON
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« Reply #10 on: May 24, 2012, 12:50:34 AM »

George in answer to your original question on do parallel dipoles work? Yes and no, if you use a combination where the other parallel wires are either high impedance or don't matter (wires for higher bands than the band you are using) then yes the combination works fine. On the other hand, if you tried to make an antenna for close spaced bands then it is not likely to be successful.

I currently have an 80/40 trapped dipole which uses parallel tuned circuits for the traps resonant on 7 MHz, it is about 108 feet long. In parallel with it, spaced off about 8 inches, is a 20m dipole. The apex of the antenna is at 31 feet and on 20m the dipole works better than a single band 20m ground plane with the feed point 10 feet off the ground (with 4 radials). On 80 and 40 the 20m dipole has no effect, except perhaps to slightly increase bandwidth due to "fatter" wire at the feed point.

The spacers for the 20m dipole are lengths of 1/4" fibreglass tube from an eBay kite supplier, I used 5 spacers on each side of the dipole with the ends tied off using thin plastic rope to the main dipole (you need an insulator on the end, otherwise the rope will de-tune the dipole when wet/icy. They are fixed to the wires with self amalgamating tape.

There is nothing special about the commerical version, except it's much more expensive than making your own!

I have some ideas about home made parallel and trapped verticals on my web site (www.astromag.co.uk/vertical) which could be doubled up to form a dipole...

73 Dave
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KJ6TSX
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« Reply #11 on: May 27, 2012, 03:00:35 PM »

Well I got the new antenna up, works much better on 20 - 80 meters  and OK on 10 meters but 17, 15,12 it doesn't work so well. On 17 meters I hear myself over the radio speakers. IT was so bad I couldn't complete the contract. My SWR is 1.6:1.  I got it down to 1:1 with a tuner but still have the same problem. I have about about 12 loops of coax in a tight circle about 12 inches in diameter to act as a choke approximately 6 feet from the rig.
I figure I am making a dumb mistake any Suggestions would be appreciated
Thanks
George
« Last Edit: May 27, 2012, 03:33:37 PM by KJ6TSX » Logged
KE4YOG
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Posts: 182




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« Reply #12 on: May 27, 2012, 03:14:03 PM »

I am runnig a double length G5RV now. It is doing good with my tuner. I am a fan of manual tuners. I will be putting up another antenna at  90 dgrees from the other. Then I can simply switch from one to the other with the tuner.  Not perfect but it should help with some nulls.
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W4VR
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« Reply #13 on: May 28, 2012, 08:53:30 AM »

These parallel wire dipoles have been in the ARRL handbook for decades.  I've never tried one but if you build your own I believe you have to play with the wire lengths to make them work on individual bands.  Once you've done that the antenna should work pretty well with low swr.
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