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Author Topic: 20 Meter Hamstick Dipole - Vertical? Feed with Twin Lead?  (Read 3572 times)
KD0PCJ
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Posts: 18




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« on: October 03, 2012, 11:44:14 AM »

There are a lot of questions in "Elmers" related to "hamstick dipoles", but I have yet to find one addressing my collection of thoughts, thus please consider the following:  I live in covenant restricted neighborhood and my attic dipole is killing me with shack RF, although a very good performer.  I am planning a second outdoor antenna system using 30ft. of easily assembled/disassembled 4' aluminum military mast sections, and two 20M "hamstick" antennas mounted with a homebrew mount (I do mostly 20M).  How should I construct this to assure best performance (I have a Johnson Matchbox to tune with and a 400W linear I can use):  a)vertical or horizontal mount?  b) feed it by coax with balun or use twin lead?  c) how should I design the mount - both sticks isolated/insulated from mount?  d) the aluminum mast would be grounded -OK or not OK? e) If vertically mounted, do I have to have the feed line angle 45 degrees away from the antenna/lower element if coax or twin-lead fed?  Any other suggestions or modifications? The XYL is watching my costs, sadly.  Thanks for the collective wisdom of the Elmers group!  Mike, de K0IVY
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WB6BYU
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Posts: 13027




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« Reply #1 on: October 03, 2012, 12:37:32 PM »

Put the elements horizontally and feed it with coax.

Insulate both elements from the mast and use a good 1 : 1 current
balun at the feedpoint.

It doesn't hurt if the mast is grounded.

Carefully tune the elements by adjusting their length so that the point
of minimum SWR (not using a tuner) is near the center of your
favorite part of the band.  Then feel free to use a tuner to extend
the coverage across the whole band as desired.

Don't expect it to cover any other HF bands, even if you can match
it with a tuner.  The efficiency will be low, which means that much of
your power will be dissipated as heat.  In fact, when you run your
amp in such a situation, the points of greatest loss may make themselves
obvious rather quickly!
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K1WJ
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Posts: 451




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« Reply #2 on: October 03, 2012, 02:02:28 PM »

I had 2 MFJ Hamtenna 20m whips - used MFJ-347 dipole mount - up 27ft in the air - used plastic folgers coffee can with 7 turns of my coax (8x) - about 6 inches from feed point. This antenna would in general out perform a Hustler 4btv ground mounted with 32 ground radials by 2 s units day in day out. Used for 18 months - worked well considering it was only 16ft wingspan - 1/2 of a normal 20m wire dipole.

I have also used a single MFJ 20m hamtenna ground mounted - 2ft off the ground with a single 1/4w counterpoise (16.5ft+-) - held up on insulator side 2ft off the ground by tripod. Also had Folgers coax choke 7 turns.
Can see a 10m & 20m set up in AZ - pic on upper right - at QRZ.com - under my call K1WJ

Both antenna's (20m) had about 150 khz bandwidth below 2:1 swr - 73 David K1WJ
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KD0PCJ
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Posts: 18




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« Reply #3 on: October 03, 2012, 05:13:38 PM »

Reference the MFJ hamtenna dipole, what would be the max. wattage this configuration could handle?  I see that true "Hamstick" brand antennas are rated at something like 600W PEP, while others are 250W.  I'd like to feed up to 400W SSB if possible. Thanks. 
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W9GB
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Posts: 2599




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« Reply #4 on: October 03, 2012, 05:31:14 PM »

Quote from: KD0PCJ
I live in covenant restricted neighborhood and my attic dipole is killing me with shack RF, although a very good performer
SOME suggestions, with your current setup.

1. USE a CHOKE BALUN at your feed point to remove Common mode RF, which is a REAL problem in your type of situation (close proximity of antenna to radio shack and living situation).

2. I have found that usage of High Pass filters, like the old Drake units OR the current MFJ-704 originally used to reduce TV interference (TVI), significantly reduces interference and neighbor issues -- even from "clean" modern radios.
http://www.mfjenterprises.com/Product.php?productid=MFJ-704

Quote from: KD0PCJ
I'd like to feed up to 400W SSB, if possible. Thanks.
I would FORGET about high power (> 100 watts) with your current living / antenna situation.
Addition RF power compounds the interference (RFI, TVI) problem you have not adequately addressed yet.
IF you get an RF hating neighbor (fear of sterilization and health problems due to your radio hobby), then your life gets real complicated!!

Quote from: KD0PCJ
The XYL is watching my costs, sadly.
IF she is contributing to overall family income and/or health-care coverage -- that is part of marriage.  You made those decisions before this question.
« Last Edit: October 03, 2012, 05:43:20 PM by W9GB » Logged
WX7G
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Posts: 5920




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« Reply #5 on: October 03, 2012, 07:13:06 PM »

The manufacturer of Hamsticks, Lakeview, is out of business. The MFJ "HF STICK" will work and is rated for 250 watt PEP.

WB6BYU has told you the best way to orient, feed, and tune your antenna.
« Last Edit: October 03, 2012, 07:15:49 PM by WX7G » Logged
KD0PCJ
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Posts: 18




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« Reply #6 on: October 03, 2012, 08:16:55 PM »

Thanks.  Ref: W9GB's suggestions - I do have a vintage E.F. Johnson filter installed, although most references say it doesn't do much this day and age (came with my vintage equipment).  Question about the choke balun at the feed point:  I use twin lead to feed a 40M attic dipole which is tuned by a Johnson Matchbox. Does not using coax to feed the antenna change things, and if not, what type would you recommend.  Ferrite beads have been liberally utilized on house audio components with some success. Thanks.     
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W9GB
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Posts: 2599




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« Reply #7 on: October 03, 2012, 09:08:41 PM »

Mike -

I just pulled up Google Maps, to see where you lived -- then I started to laugh.
Your subdivision (and house) was still corn fields and dreams,
when I left Mercy Hospital and moved back to Illinois & Chicago in 1995.  
Scott Blvd. was the new eastern border, at that time.


Twin lead (300 ohm?) from the feed point, you should still be balanced into your tuner,
BUT a coaxial feed is probably a better solution in your situation.

Did you try to keep antenna away from metal (AC conductors parallel, etc.)??

w9gb
« Last Edit: October 03, 2012, 09:23:25 PM by W9GB » Logged
WB6BYU
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Posts: 13027




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« Reply #8 on: October 03, 2012, 09:40:01 PM »

Quote from: KD0PCJ

I use twin lead to feed a 40M attic dipole which is tuned by a Johnson Matchbox. Does not using coax to feed the antenna change things, and if not, what type would you recommend. 



Feeding a wire antenna with twinlead allows it to be used on several bands by just
adjusting a tuner in the shack.

However, that doesn't work well with a shortened / loaded antenna like a mobile whip.
The antenna is roughly 3' of wire, 1' of coil, and 4' of whip,  when the antenna isn't
resonant the coil looks like a big RF choke, leaving 3' of wire on either side of the
feedpoint to use on the other bands.  That's a far cry from a full-sized dipole which
would be 16' on the other bands.

Since the antenna will not work well on more than one band, there isn't much to
be gained by feeding it with twinlead.  (You still can do so if you want.)  With coax
feed, once the antenna is adjusted you can use much of the band without needing
an antenna tuner.

Depending on how far it is from the shack to the antenna, RG-58 will probably work,
but RG-8X would be a reasonable compromise among cost, loss, and power handling
capability.  RG-6 TV cable will work, though you might still need the tuner depending
on the length.
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KD0PCJ
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Posts: 18




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« Reply #9 on: October 04, 2012, 10:01:59 AM »

Thanks, Gents.  I will proceed with my plan to orient the MFJ-1620T's horizontally and coax feed it with 1:1 balun near the feed point.  At a shade over 30ft. high (~1/2 wave), I'm thinking (and hoping) I'll get more than a cloud burner. 

P.S.  I read an interesting article in Ham Universe about orienting these in a V pattern horizontally supposedly netting "mini-beam" performance.  From what I read, a dipole has its best propagation broadside anyway when at least 1/2 wave above ground. Folks put rotors on stick dipoles.  Hmm...I'll need convincing on the worth of that.   
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WX7G
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Posts: 5920




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« Reply #10 on: October 04, 2012, 11:13:57 AM »

Your dipole will exhibit good directivity and a rotator would be a nice addition.
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WB6BYU
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Posts: 13027




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« Reply #11 on: October 04, 2012, 11:28:49 AM »

Quote from: KD0PCJ

At a shade over 30ft. high (~1/2 wave), I'm thinking (and hoping) I'll get more than a cloud burner. 



You should get pretty good performance at that height.




Quote

P.S.  I read an interesting article in Ham Universe about orienting these in a V pattern horizontally supposedly netting "mini-beam" performance...
  


That's true - you can read such articles in Ham Universe, along with many others that
are just as contrary to the laws of physics.  But technical rigor is not a requirement to
publish an article on the Internet.

A vee beam can have gain when the legs are physically about 1 wavelength long, or longer.
That's not the case with your antenna, or with the one in the Ham Universe article.
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K8AC
Member

Posts: 1465




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« Reply #12 on: October 05, 2012, 06:12:08 PM »

I'm always puzzled over the infatuation with dipole or yagi antennas created with Hamsticks.  Why would you do that?  If you can get away with putting up the 30' mast, install an inverted vee cut for 20M at the top of the mast and feed it with 300 ohm TV feedline if you can still find it, or use the window-type ladder line if not.  Feed it with a balanced tuner or an imbalanced tuner with a ferrite balun at the output of the tuner.  You'll be amazed at how well it will work compared to the Hamsticks.  You can make the antenna out of very small gauge wire and it will be practically invisible. 

73, K8AC
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NR4C
Member

Posts: 306




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« Reply #13 on: October 09, 2012, 09:00:47 AM »

Save your self a bit of cash and get some wire (32ft) and put up a 20 meter dipole and follow WB6BYU's excellent suggestions on setting up and operating.  You'll need some line to tie the ends to something in the attic (for indoor use, even common 'mason twine' or 'chalk line' will work), the ends can droop or bend as needed to fit the space.   You can make a  center connector from a piece of plasatic "cutting board" from the kitchen.  I have used plastic toothbrush handles for this.  It always works better if you made it yourself.

Might even try to put it up outside, as #16-18 wire gets pretty small and hard to see, especially with trees in the background.

...bill  nr4c

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NO2A
Member

Posts: 758




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« Reply #14 on: October 09, 2012, 09:24:30 AM »

I'm always puzzled over the infatuation with dipole or yagi antennas created with Hamsticks.  Why would you do that?  If you can get away with putting up the 30' mast, install an inverted vee cut for 20M at the top of the mast and feed it with 300 ohm TV feedline if you can still find it, or use the window-type ladder line if not.  Feed it with a balanced tuner or an imbalanced tuner with a ferrite balun at the output of the tuner.  You'll be amazed at how well it will work compared to the Hamsticks.  You can make the antenna out of very small gauge wire and it will be practically invisible. 

73, K8AC
Not only is this a much better radiator,it usually eliminates any rf in the shack problems,due to it being a balanced antenna.
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