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Author Topic: Arctic QRP antenna ideas?  (Read 2730 times)
VE3VID
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Posts: 145




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« on: November 04, 2012, 07:41:27 AM »

Hi and thanks for reading my post

I want to build an effective QRP antenna for a challenging environment.  I will be in the Canadian Arctic near the top of Baffin Island.  The only rig I can take is a 20m 5 watt PSK radio.  I can get a wire antenna up about 30ft off a balcony either sloped or strung over to another point about 100ft away.  Supports are a challenge, clearly.  For this reason I wonder if an end fed antenna would be best, or perhaps something with a counterpoise dangling at right-angle?  Something that will resonate well at 14070, and the tuner feeding twin lead can bring the impedance in line.

Any ideas would be really appreciated
cheers

David
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KB1GMX
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« Reply #1 on: November 04, 2012, 08:44:11 AM »

A wire for 20M is 31.5 feet (little over 9.6M) so supports are generally easy and a single support
that is 30ft high and sloping down can work.

I would suggest a 20M end fed half wave and a colapsable breem/crappy/fiberglass outrigger pole.
That antenna can be oriented vertical, horizontal, V (inverted or upright), or as an L easily.
That antenna is about 31ft long minus cable.

You didn't say high high the balcony is so if the pole is short say 20ft and it's high (2nd or third story)
you can let the end dangle when the pole is horizontal or 30-45 degrees up.

If you are really high 4th story or higher.. you can let the wire just dangle outside as far from
the building as possible.


Allison
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WB6BYU
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Posts: 13243




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« Reply #2 on: November 04, 2012, 09:02:30 AM »

One of the collapsible fiberglass fishing rods might make a useful support
for a vertical wire.  You may have to tape the joints to keep it from
collapsing on its own in the wind.

But my first question would be about the desired direction you want
to work:  some antennas are going to be directional (especially long
wires) and if you want to work stations in a specific area you will
want to consider the patterns.

My standard QRP antenna kit is a dipole.  I have a center insulator
on the end of the coax and add wires for whatever set of bands I
want to operate each time I set up.  For your purpose, an inverted
vee with the feedpoint on the balcony and the wires tied off to
whatever supports you can find is probably one of the simplest
approaches.  If you take a roll of Mason's Line or other stout string
you can tie them off at ground level and still keep the ends of the
wires at a reasonable height.  Actually one advantage of having
all the different wires available was that I could use them for
creative designs when situations allowed:  a 40m dipole wire could
be pressed into service as a full wave loop on 10m.

A 100' long wire will have maximum lobes roughly 35 degrees from the
ends of the wire (about 3 half waves long on 20m). There is a narrow
broadside lobe, but otherwise radiation will be better within 45 degrees
of the ends than otherwise.  The impedance will be high, so a small
L-network tuner will allow a good match, and a couple 1/4 wave radial
wires running off each side of the balcony and dropping down from
there will help reduce common mode current problems.  Actually you
can use shorter wires and just extend them with rope to the support,
allowing some room for adjusting the pattern and/or adapting to
different circumstances.

Another option might be a twinlead J-pole:  they are much more common
on 2m, but the first one I built was for 15m and it worked well.  That
gives you the ability to use an end-fed antenna with coax feed.


In the end, what will probably give you the best results is to have a
number of options available.  I'd suggest at least having a dipole plus
a length of strong, flexible wire and a small tuner, along with enough
rope to handle a number of situations.

I operated my Argonaut from several logging camps in Alaska many
years ago - not quite as extreme as where you are, but I never knew
when I might get shipped out to another camp, and had to be
adaptable.  (Supports were also a problem, as all the trees had
usually been logged around the camps.)  For multi-band use I
usually ended up with long wires, and just made contacts with
wherever the pattern happened to point.  But longer antennas
aren't as attractive when you have the potential for snow and
ice loading:  an inverted vee made with Teflon-insulated wire
may survive better in such cases.  (With a loop antenna you
can run current through the wire to melt the ice.)

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K3VAT
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Posts: 709




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« Reply #3 on: November 04, 2012, 10:59:33 AM »

I want to build an effective QRP antenna for a challenging environment.  ...
...
Any ideas would be really appreciated.  cheers David

...
My standard QRP antenna kit is a dipole.  I have a center insulator
on the end of the coax and add wires for whatever set of bands I
want to operate each time I set up.  For your purpose, an inverted
vee with the feedpoint on the balcony and the wires tied off to
whatever supports you can find is probably one of the simplest
approaches. 

This would be my approach.

...
I would suggest a 20M end fed half wave and a colapsable breem/crappy/fiberglass outrigger pole.
...

I would avoid any type of end fed antenna; I know, they're some good reviews here on eHam.net, but are in fact no competition to a dipole.  Properly installed, the dipole, especially one resonant on your favorite band presents very little difficulty for matching.

...  I'd suggest at least having a dipole plus a length of strong, flexible wire and a small tuner, along with enough rope to handle a number of situations. ...

Sound advice.  Your rope should be Dacron cord or something similar:  3/32 or 1/8 is plenty, even with those 75 mph winds blowing off the Arctic cap.

GL, 73, Rich, K3VAT
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WX7G
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« Reply #4 on: November 04, 2012, 03:20:43 PM »

Keep it simple.

As WB6BYU says I suggest an inverted-V. Run the ends of the insulated line extensions (fishing line for example) to whatever there is or to the ground. Simple and effective. Feed it directly with coax or through a 1:1 balun if you care about such things.
« Last Edit: November 04, 2012, 03:23:10 PM by WX7G » Logged
VE3VID
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Posts: 145




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« Reply #5 on: November 04, 2012, 03:24:50 PM »

Thanks everybody for those replies.

The supports are the biggest problem, and getting the feedline outside.  There is only one balcony, 30ft above ground.  About 100ft away is an exterior staircase almost as high as the balcony.  Nothing else.  This is why I was asking about end fed.

I have about 20ft of 300 ohm twin lead that will fit through the balcony door to the antenna, a roll of 150lb Dacron, and a tuner with balun feed points.  What about an off center fed dipole?  3 x half waves (46ft) horizontal to the other support, and a half wave on the short leg just dangling down from the feed point?

Will be happy to make some contacts from VY0 to anyone who can copy my signal  Smiley
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WB6BYU
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« Reply #6 on: November 04, 2012, 05:24:54 PM »

Quote from: VE3VID

The supports are the biggest problem, and getting the feedline outside.  There is only one balcony, 30ft above ground.  About 100ft away is an exterior staircase almost as high as the balcony.  Nothing else.  This is why I was asking about end fed.




If you put the feedpoint of a dipole / inverted vee on the balcony (perhaps supported
off the edge on a length of pipe) and anchor the support ropes on the ends of the wires
some 60' away in each direction, it should work pretty well even without any other
supports.

End fed wires can be quirky.  I've often used them, sometimes with good results, but
they aren't quite as convenient as they might seem.  I've often needed one or more
quarter wave radials at the feedpoint and/or at the rig to tame the RF in the shack
(even running QRP).  But you can certainly try one:  the length will determine the
radiation pattern.  You can run the end of the wire directly to the output terminal
on a tuner (with a couple quarter wave radials attached to the ground lug) or you
can use about 13.5' of the twinlead as a Zepp feed (which works best when the
antenna is a multiple of 1/2 wave long.)  This isn't ideal, but sometimes I've gotten
it to work when other options didn't.



Quote

I have about 20ft of 300 ohm twin lead that will fit through the balcony door to the antenna, a roll of 150lb Dacron, and a tuner with balun feed points.  What about an off center fed dipole?  3 x half waves (46ft) horizontal to the other support, and a half wave on the short leg just dangling down from the feed point?


3/2 wave and 1/2 wave isn't a particularly good combination.

You could try 3/4 wave (51') in one direction and a 1/4 wave radial (17')hanging
down (or tied out to a stake as suggested above.)  That gives you a low
feedpoint impedance that will work with coax feed.  Whether that is any better
than a dipole depends on the relative directions:  the 3/4 and 1/4 wave antenna
will have maximum roughly 45 degrees to the direction of the wire (as will a
full wave wire when end-fed) while the standard dipole will have maximum
radiation broadside to the antenna.

You can use a short length of 300 ohm twinlead to get through the door
and splice it onto coax at each end.  Or you can use copper sheets or
tape where you have even less clearance.


Again, my recommendation would be to have a dipole handy that you can string
off the balcony to get you started, as well as additional materials (wire, rope,
feedline) to get more creative as circumstances permit.

And do consider that direction you would want to work relative to the far
support:  broadside would call for a different approach than off the end
or at an angle.
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KB1GMX
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Posts: 772




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« Reply #7 on: November 04, 2012, 07:08:03 PM »

K3VAT <<I would avoid any type of end fed antenna; I know, they're some good reviews here on eHam.net, but are in fact no competition to a dipole.>>

Ah, its the same antenna..  The only difference is the feed point.  Both are resonant antennas
and both are half wave.  I did specify an end fed half wave.   If you use the PAR/LNR design
you do not need any additional matching network.   I happen to use a PAR EF40/20/10,
and an EF40, never had RF issues at power level up to 100W for the 40 and up to 50W SSB for
the 40/20/10.   I use the 40/20/10 here with one end supported by a 30ft tower to a tree
(flat top) and my other one is the one I drag to everywhere including two field days.  If the
PAR/LNR price puts you off its a very easily home made.   AA5TB has multiple write ups on this at
http://www.aa5tb.com/efha_wrk.html.

One note.. the wire must be a electrical half wave and not just nearly a half wave (resonant)
or the end result is a random length long wire with random results usually including RF issues.

There are other non resonant designs (26, 43, 88ft long)  for end fed wires out there that might
present problems like needing a counterpoise and lower effective gain.  I tend to not suggest them.
They are popular for multiband use at high power where one wire is it and compromise is tolerable.

I'd also vote for a standard half wave center fed but for a few reasons.  One if you have a single
point mount where you support the coax.   Remember it is best to have the coax leave the
antenna perpendicular for at least a quarter wave.   If you bring the coax back to the point of
origin  of one  of the support points it is then parallel to the one leg of the antenna, not good.
If you are under the antenna great.  If you are not that means at least 16ft of additional coax
to haul around.  Also it is much harder to hang a centerfed half wave dipole vertically and
meet the requirement of keeping the coax away and not parallel.  As a V fed at the balcony
and the ends tied off on the ground far enough apart may work.  However its signal is blocked
on one side by the building and likely a metal one or containing metal or foil.

A twinlead Jpole for 20m is the same antenna save for its roughly 49ft long and its still an
end fed half wave with a transmission line stub transformer match.  Not recommended for
size alone.

Long wires work but the main issue is needing an adjustable tuner to match them and maybe
a ground/counterpoise to work against.  Advantage is they are multiband, usually.  Disadvantage
more stuff and long.  Since you are doing 20M PSK31 this approach may not be any advantage.

The breem/crappy/fiberglass outrigger pole is the collapsible fiberglass pole that is often use for
portable work.   What works nice is if a end fed half wave wire can be run up the center and
the pole is long enough.  I have one that's 20ft I use for 10M (wire is about 16.4ft) and
the match box is at the end.  Shrinks to less than 4ft in minutes.  For longer wires there are longer versions or it can hang off the end as a sideways L.

Whatever you do try it or several at home and get used to how they tune and what you need
to make the selected antenna work at the site.  Bring rope or 5/50 (paracord) as it's handy for
this kind of field work.


Allison
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G4AON
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Posts: 529




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« Reply #8 on: November 05, 2012, 02:50:30 AM »

I operate 20m overseas at least a couple of times a year, in the early days I used a dipole but found it mediocre for most medium to long distance contacts as I couldn't get it any higher than about 20 feet, the resultant take off angle was quite high.

These days I use a ground plane mounted on a balcony, they only need 2 radials and are easy enough to make. The DX and medium distance performance will be better than a dipole at a similar height and it will be omni directional.

I use a fishing pole for a support, but I understand fibreglass and below zero temperatures don't mix... So you might need to make something from aluminium, perhaps an old CB half wave vertical could be altered to give a 16 foot 6 inch (approx) vertical and use a couple of 16 foot 6 inch wire radials. Would you need to pre-tune the antenna at home and it should just "go together and work" on site.

A quick look on EZNec gives a take off angle around 33 degrees for a horizontal dipole up about 30 feet, and 14 degrees for a ground plane with the base at 30 feet.

73 Dave

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K8AG
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Posts: 351




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« Reply #9 on: November 05, 2012, 11:52:18 AM »

I have an article in the current QRP Quarterly about constructing a 20M and a 3-band 40/30/20 meter antenna out of cheap Radio Shack speaker wire.  For 20 meters simply unzip a quarter wave, tie a knot as a center insulator.  You could dangle one hale and string the other out to your support.

Use the remaining zip cord as feed.

72, JP, K8AG
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K9JWV
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Posts: 5




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« Reply #10 on: November 06, 2012, 06:05:02 AM »

The original post wrote this:

I want to build an effective QRP antenna for a challenging environment.  I will be in the Canadian Arctic near the top of Baffin Island.  The only rig I can take is a 20m 5 watt PSK radio.  I can get a wire antenna up about 30ft off a balcony either sloped or strung over to another point about 100ft away.  Supports are a challenge, clearly.  For this reason I wonder if an end fed antenna would be best, or perhaps something with a counterpoise dangling at right-angle?  Something that will resonate well at 14070, and the tuner feeding twin lead can bring the impedance in line.

The majority of the replies forgot to understand the requirements:

- wire antenna off a 30 ft balcony that's sloped or strung over to another point 100 ft away
- it's friggin' COLD up there
- supports are a challenge!
Note: I'll save comments on that "twin lead" business till last.

The poster goes on to posit that an end-fed antenna would be the best, albeit something with a counterpoise might work!

THE antenna for his situation clearly is an end fed half wave, especially since he's operating at QRP levels! I say that 'cuz there is a small and efficient EFHW antenna tuner produced by Stu, KI6J, that will do the job of him and it's an inexpensive investment.

An EFHW antenna will perform exactly as a dipole (a dipole that's strung in the same direction and height) - there is NO difference in radiation patterns for either antenna.

An EFHW antenna that's cut very close to the recommended length will need little in the way of a counterpoise - if you want to tie a counterpoise on to the ground terminal of your tuner, fine...make it abouta foot long 'cuz that's all you'll need.

An EFHW antenna doesn't require running a lot of coax out to the center point (difficult to do if your faced with one tie point out some distance.

Erecting an inverted Vee antenna where one of the sides would be located close to the hotel building does not sound like an efficient way to use that sort of an antenna!

Aside notes:

EFHW antennas are seeing a resurgence in popularity due, mainly, to the myriad SOTA activators who use QRP rigs.

An EFHW, in my view, based on many SOTA activations while using the KI6J tuner, is the way to go for single band /p operations.

Regarding the mention of twin lead - I don't know if the original poster was thinking he needed to use twin lead or is that the only type of feedline he owns?!?!?!  If twin lead is all he owns then I guess he'd need a 6:1 balun (if 300 ohm) or a 9:1 balun (if 450 ohm) inserted at the end of the twinlead with a short length of coax from the balun output to the EFHW tuner.  If he has a short length of coax to run from inside the hotel room out to the balcony ---- it's Miller time!

Contact Stu, KI6J, as he might be able to construct a cobbled up balun/EFHW tuner combination for this operation - Stu is fairly creative.

72, Jim Rodenkirch K9JWV
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VE3VID
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Posts: 145




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« Reply #11 on: November 06, 2012, 03:22:59 PM »

Thank you all again for the fine input on this subject.

Though a vertical antenna sounds promising I am leery about keeping it mounted to the balcony rail in the high winds of an arctic winter.  I do have a tuner with balanced feed points.  A recent suggestion (which keeps things ++simple) would be a 300ohm twin lead folded dipole.  Since there is a lot of polar opinions (pun intended) about end-fed wires.  Twin lead would get out the building easier than coax;  its lighter so even if it dangled from a non supported feed point there would be less weight; antenna and feed line match at 280/300 ohms, low loss etc.

Opinions?

BTW - I am on Igloolik Island.  I wonder if its ever been activated under IOTA.  For now its -27c outside, home in a week.
David
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WB6BYU
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« Reply #12 on: November 06, 2012, 04:32:29 PM »

Twinlead is lighter than some types of coax, but has higher wind loading,
and the fluttering can cause physical stress on the wires if it doesn't have
good strain relief.

You would probably be better off using twinlead to feed a standard wire
dipole, as the wire would have lower wind loading and likely would survive
better than a twinlead folded dipole.  That also allows you to load the
antenna on other bands should you so choose.
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N8CMQ
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Posts: 355




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« Reply #13 on: November 06, 2012, 06:55:04 PM »

  If it were me, I would make a dipole and try to
get it vertical. Maybe get a loop around a vent pipe
for the upper support, and tie off the bottom as well.

  You should use coax for the antenna if possible.
But if you have to use ribbon twin-lead, you need
a matching transformer.
However, if you are going out the sliding door to the
antenna, chances are, the twin-lead SWR will be
too high.
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