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Author Topic: Multi band ballanced antenna system, Questions  (Read 1837 times)
K3JVB
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« Reply #15 on: August 11, 2008, 06:52:28 PM »

..point being, I used the coax to bring it through a Stucco wall. And past a slew of pipes, and wires in the basement, to the shack.
73
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N5YPJ
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Posts: 643




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« Reply #16 on: August 12, 2008, 06:50:50 AM »

If the antenna is allowing you to make decent contacts and is designed within good engineering practices which it sounds like it is from your description, I wouldn't mess with it.

Here I use a 1:1 balun with 8 ft of coax going into the shack and 96 ft of 450 ohm ladder line feeding a 102 ft dipole. Some frequencies are difficult to tune but do tune with patience. This is not my primary antenna but it does get used a few times a week and good stateside contacts are made.

I would like to point out though a dipole configured as an inverted vee and being used on multiple bands has strong tendencies to radiate at higher take off angles as the frequency goes higher and in some cases becomes useless.
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W5DXP
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« Reply #17 on: August 12, 2008, 08:09:58 AM »

> KC8BYF wrote: Wish my antenna could go up higher to accommodate the 100 ft. length of 450 ohm line.

There's an easy way to "coil" ladder-line using a non-conductive messenger line. Let's assume you want to "coil" 100 feet of ladder-line into a linear distance of 50 feet. Spiral the ladder-line down the messenger line at the rate of two feet of ladder-line per one foot of messenger line. That would be one turn per foot with a diameter of about six inches. Tie a knot in the messenger line every foot and use a black plastic tie-wrap at every knot. That's what I do and it's extremely easy.

If spiral turns of ladder-line are kept at least six inches apart, ladder-line can certainly be "coiled".
--
73, Cecil, w5dxp.com
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My antenna says, "What makes me happy is when the tuner is adjusted for maximum available current through my radiation resistance!" 73, Cecil, w5dxp.com
KZ1X
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Posts: 3333




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« Reply #18 on: August 12, 2008, 11:40:44 AM »

KC8BYF says:
"I would ultimately like to have a remotely tuned balanced tuner at the base of the tower. However, this introduces too many "points of failure" possibilities."

KZ1X asks:
It does? What would they be?

Answer:
mainly component failure would be the biggest concern here at my installation.

) bad kids in the neighborhood

>>> Who would pull down the wires before they did anything else.

) power supply

>>> Power supply is your shack 12V supply, no problem there

) cables to remote unit

>>> there is only one cable needed, the coaxial feedline you need anyway, which should be buried

) inside "switching apparatus"

>>> there is none; a simple, passive power inserter allows you to phantom the DC power to the remote tuner (such as the MFJ-927; see the QST product review due out any day now)

) stepper motors

>>> there are no stepper motors, and even if there were, stepper motors are VERY reliable ... you need to look at how remote autocouplers work, using latching relays

) indicators for stepper motors

>>> None are needed; remote autocouplers are fully automatic and the rewards of their effort shows up as a 1;1 match onto your 50 ohm coax

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N1LO
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« Reply #19 on: August 12, 2008, 01:33:00 PM »

Tinkering is the fun part! Sometimes I enjoy the building/inventing part more than operating on the air.

Keep in mind that perfect is the enemy of good enough.

What you have now is darn near perfect. Sounds like you're so jazzed up by your success that you want another project to build.

Definitely get EZNEC, and buy it so you can model more than a dipole. You can play 'what if' to your heart's content.

I also vote for a horizontal loop. I like 270 ft for 80-10. Check out the patterns yourself and see if you don't agree that it's a lot better than a 135' doublet.

Try moving the feedpoint of your doublet off center to 45' from then end (45' & 90' legs). This should take a lot of stress off of your tuner by limiting impedance extremes.

Build a switchable 1:1/4:1 current balun and use the ratio that best suits each band (www.qsl.net/n1lo/build.htm)

Keep tinkering and having fun!

GL,

Mark
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AA4PB
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« Reply #20 on: August 12, 2008, 03:33:42 PM »

I agree with K8AC on the "points of failure". I've had an SG-230 outside for nearly 20 years with only one failure and SGC fixed that for free. Before the SGC I had a military surplus tuner out there and never had a problem. I only replaced it because it was slow (motors driving capacitors and inductors).
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Bob  AA4PB
Garrisonville, VA
N5YPJ
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Posts: 643




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« Reply #21 on: August 12, 2008, 04:51:19 PM »

I can't recommend an MFJ-993B auto tuner for remote use. An 80 cent component in mine got zapped and it cost me about $80 including S&H X2 to get it repaired. In the shack it's a good unit.
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N8NSN
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« Reply #22 on: August 15, 2008, 07:25:42 AM »

W5DXP and N1LO... A thank you of special consideration...

Thanks to both of you per your suggestion to try my hand with EZNEC !  I found a free down load for the newest version (5.1) and have been really enjoying the program.  Thus far, I have only the trial version and it is limited to only 20 segments total on any design.  This makes it rather difficult to really get accurate results on the system unless the antenna is kept very short and very simple.  It is a good tool to learn the "system" with, however.  Now I am VERY interested in purchasing the pro series of the EZNEC which opens up the gates to using 20,000 segments !  Wow !

1 thing I didn't like, thus far, with EZNEC is that there doesn't seem to be any "automatically set" perimeters for certain types of feed lines, such as, 300, 450, 600 or 800 ohm parallel lines... For parallel feeders a person has to apply their own "sources" in the circuit as individually placed wires.  This requires quite accurate critical spacing of the wires at their set distances and lengths to accomplish the desired feed line impedance ...etc.  It would be much simpler if the "feed line" category were inclusive of parallel feeders one could select and designate a length and impedance and go from there.  Perhaps, the "non-free" (pro versions) of the program has such a feature.  Or maybe I just haven't discovered a way to accomplish this task in a user friendly way.

I did manage to accurately place this 135' doublet into the trial version accurately as only 20 segments would allow over the past few days learning the system.  Now, I understand a LOT more about why this antenna works.  The "plotting" of the antenna and it's gain characteristics are quite satisfactory for a multi-band single antenna system.  The whole concern on "what bal-un to use" was very much a waste of my faculties.  The 4:1 bal-un is quite satisfactory for the application here at this location...for now.  I am not getting any "saturation" problems with only running 100 watts.  Ultimately if this antenna survives my experimentation fetish; I will, most likely, eventually work a remotely tuned balanced coupler into the system for optimal efficiency.

Working with EZNEC has satisfied my thirst for "tinkering".  As well, EZNEC has added "method to my madness"  Cheesy\\

73 !

KC8BYF jimmie
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