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Author Topic: Considering an inverted V in a confined space  (Read 565 times)

KK4GMU

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Re: Considering an inverted V in a confined space
« Reply #15 on: January 07, 2022, 08:54:27 AM »


I have used PVC for antenna supports, but I generally
don’t think it is a good solution.  It is relatively heavy
and bendy.   Black ABS pipe is lighter and stiffer - stop
by your local store and try holding each type of pipe
horizontal from one end, and you will see what I mean.

ABS has a minimum size of 1 1/4 or 1 1/2 inch.  It will
bow, however, if you try to tighten the guy ropes too
tight.

Fiberglass is a better solution.  There are any number
of fiberglass fishing poles sold for this purpose, with
popular heights of 20’ to 33’.  (SpiderPole sells heavy
duty versions up to 80’.)  The top section is often
too wimpy to support an antenna, so don’t plan for
the full advertised height.

With a bit of creativity, you might
fit a 33’ dipole for 20m into that space, or even
a coil-loaded dipole for 40m (which could also
work 10m).  But, unless you feed tha antenna
with twinlead or ladderline instead of coax, the
performance won’t be very good on other bands.
(A 15m dipole probably wouldn’t be too bad on
17m or 12m, but will degrade much beyond that.)

One of the common options is a painter’s pole,
but make sure you can raise the top section
with the bottom section vertical.  The taller ones
use 8’ sections, which may require a ladder.

My favorite is in the window washing section of
Home Depot - the Unger 24’ telescopic pole,
UPC 61475-97298.  It is aluminum with a
triangular cross section, and has thumb locks
on the sections instead of twist locks.  There
are numerous other telescoping handles of
varying sizes - I also have a 15’ one for
changing light bulbs.  Probably the best
deal was a red and green 13’ pole designed
for stringing Christmas lights, that was on
super sale on 27 December.

[...with metal poles...] There can be some interaction right at the feedpoint
that can shift the tuning a bit.  You can always add
a foot or two of PVC between the top of the mast and
the feedpoint if you want.  (It is fine for short lengths.)
I sometimes use a wood spacer at the top to move
the feedpoint away from a metal mast a little bit,
but I don’t think it really makes much difference.

Some of the telescoping poles don’t make good
electrical contact between the sections, so they
don’t act like a long piece of metal.
Thanks!

I didn't see any black ABS at my local Lowes, but I did see some perfect looking telescopic painter's poles 12' long, which is the maximum height I'd feel comfortable with without attracting too much attention from my HOA.  The bottom section is fiberglass, and the top section is aluminum.  There is a medium duty for $20 and a heavy duty, thicker version for $40.  If the inverted V was the only thing attached, the medium duty would be fine.  But I'd probably go for the heavy duty one because I have a couple additional items to attach.  One is a wireless weather station at the top, and the other is an FM antenna I'd mount about midway.  The inverted V would be mounted a few inches below the weather station - about 11' high. Here is a great "what not to do with poles" post. https://www.dj0ip.de/spiderbeam/fiberglass-spiderpole/kill-my-pole/

Ideally both sections would be fiberglass.  So I'll have to deal with some RF squirrellyness with the feed point being near the aluminum, I guess.  But, I have time to look for additional alternatives and know a fair amount of experimentation is involved. 

What are your thoughts about the MFJ-993B "Intellituner" that accommodates both balanced ladder line and coax along with a 10:1 balun, instead of the MFJ-939 that just accepts coax? https://www.gigaparts.com/mfj-993b.html  For $100 more, might the additional flexibility be worthwhile?  Or are there better, more cost-effective tuning options?

Thanks all for all the feedback.
« Last Edit: January 07, 2022, 09:06:29 AM by KK4GMU »
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KK4GMU

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Re: Considering an inverted V in a confined space
« Reply #16 on: January 07, 2022, 09:31:54 AM »

Pole from Lowes:  https://www.lowes.com/pd/Mr-LongArm-Pro-Lok-8-4-ft-to-23-2-ft-Telescoping-Threaded-Extension-Pole/4755038 

3-section; extends from 8'4" to 23' 2"; fiberglass lower section, aluminum upper.  Perhaps add a 1 foot long PVC at the top for mounting the feed line. 

Not yet sure whether to use coax or balanced ladder line.  The run would be about 20' from the feed point to the outside wall of the shack where it would connect to RG8 and run another 15' to the rig.
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WB6BYU

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Re: Considering an inverted V in a confined space
« Reply #17 on: January 07, 2022, 11:55:12 AM »

Quote from: KK4GMU

...3-section; extends from 8'4" to 23' 2";



The problem with an 9' minimum pole is that I can't reach the
top to extend the sections when the pole is vertical with the base
on the ground (unless I stand on a ladder).  That means I have
to extend it horizontally, then tip it up into place, unless there
is something convenient to stand on.

That's why I would look in the window washing section of the
store and see what you can find with a minimum length of 6'
or so instead.

Quote

...Not yet sure whether to use coax or balanced ladder line.  The run would be about 20' from the feed point to the outside wall of the shack where it would connect to RG8 and run another 15' to the rig.



I don't know that you will gain much if the ladder line is that short,
especially with a relatively long piece of coax on it.  My preference
is to bring the ladder line all the way in to the tuner.

That's because the ladder line will transform the antenna impedance
(it won't match the impedance of the antenna on any band), then
the coax will transform it even more.  With the wrong combination
of lengths, a 50 ohm antenna impedance can end up as around 1 or
2 ohms at the tuner, which isn't good for efficiency, even if the tuner
can manage to match it.  The same antenna fed with ladder line the
whole way will be somewhere between 50 ohms and 4000 ohms -
still might be outside the matching range of your tuner with some
lengths, but it avoids the very low resistances.

And that evaluation needs to be done for each band as the electrical
lengths change with frequency.

KL7CW

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Re: Considering an inverted V in a confined space
« Reply #18 on: January 07, 2022, 10:04:35 PM »

ABS pipe.  This is always in the plumbing section of the box stores and is black.  If you could make each leg of the inverted V about 11 feet long, it would be near resonance on 15 meters.  If you feed it with an ELECTRICAL half wave of ladder line, the 50 ohm Z of the V would be about 50 ohms at the end of the ladder line, even if the line is say 400 or 600 ohm Z.  With the velocity factor of the ladder line or transmitting twin lead (400 ohms ?) this would probably be roughly 20 feet of ladder line.  Thus very easy to match with the tuner on 15 meters, and probably not too awful on 17 and possibly other bands. A fiber glass pole might be a better option, strong, thin, non conductive, so you could even run the twin lead right down the pole.  This would change the Z, but a half wave line just repeats the Z at the other end.  This is just an idea to think about.  If you design the V and twin lead for 17 meters, this may be close enough to a half wave on 20 and 15 also for a tuner to reasonably match.  Be sure to locate the tuner at the end of the twin or ladder line.  If for some reason the tuner does not "like" the antenna on a particular band, just changing the length of the twin lead by a foot or two often will make it much easier to match.
   If you want to operate 40 or 80, you could just open the twin lead up part way up the pole, tie the conductors together, hook them to a wire which runs down either to ground level or perhaps the top rail of your metal fence, and feed this into a tuner or home brew network.  The metal top fence rail may make an adequate counterpoise/ground for the top loaded vertical, or you could feed the antenna against a few radials buried or laying on the ground.  We are hams, so try everything.  Sometimes "good ideas" do not work, and "bad ideas" happen to at least get you on the air.  Any of the ideas presented, are probably not efficient antennas, but some of the ideas submitted by various folks, may at least get you on the air.
             Rick  KL7CW
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KK4GMU

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Re: Considering an inverted V in a confined space
« Reply #19 on: January 12, 2022, 01:29:12 PM »

ABS pipe.  This is always in the plumbing section of the box stores and is black.  If you could make each leg of the inverted V about 11 feet long, it would be near resonance on 15 meters.  If you feed it with an ELECTRICAL half wave of ladder line, the 50 ohm Z of the V would be about 50 ohms at the end of the ladder line, even if the line is say 400 or 600 ohm Z.  With the velocity factor of the ladder line or transmitting twin lead (400 ohms ?) this would probably be roughly 20 feet of ladder line.  Thus very easy to match with the tuner on 15 meters, and probably not too awful on 17 and possibly other bands. A fiber glass pole might be a better option, strong, thin, non conductive, so you could even run the twin lead right down the pole.  This would change the Z, but a half wave line just repeats the Z at the other end.  This is just an idea to think about.  If you design the V and twin lead for 17 meters, this may be close enough to a half wave on 20 and 15 also for a tuner to reasonably match.  Be sure to locate the tuner at the end of the twin or ladder line.  If for some reason the tuner does not "like" the antenna on a particular band, just changing the length of the twin lead by a foot or two often will make it much easier to match.
   If you want to operate 40 or 80, you could just open the twin lead up part way up the pole, tie the conductors together, hook them to a wire which runs down either to ground level or perhaps the top rail of your metal fence, and feed this into a tuner or home brew network.  The metal top fence rail may make an adequate counterpoise/ground for the top loaded vertical, or you could feed the antenna against a few radials buried or laying on the ground.  We are hams, so try everything.  Sometimes "good ideas" do not work, and "bad ideas" happen to at least get you on the air.  Any of the ideas presented, are probably not efficient antennas, but some of the ideas submitted by various folks, may at least get you on the air.
             Rick  KL7CW
Thanks for your encouraging post.  The retractable pole I just installed is fiberglass on the bottom half and aluminum in the upper half.  I will use the traditional stand offs for the ladder line on the aluminum portion, unless there is a reason not to in which case I will make a couple of them out of pvc.
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KK4GMU

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Re: Considering an inverted V in a confined space
« Reply #20 on: January 14, 2022, 08:30:51 AM »

With all the great advice I've received on these antenna/HOA threads, I'll keep busy for months experimenting, learning and refining.  I appreciate all the comments.

I expect the antenna selection soon after consulting with a couple of local hams in the Marion [County] Emergency Radio Team (MERT) who also have local HOA experience.

My antenna research time is competing with my General study time :o so I may not be on the air till May ;D
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