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Author Topic: Portable QRP antenna ideas?  (Read 4261 times)
N5LXI
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Posts: 59


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« on: February 21, 2001, 12:54:04 AM »

I have a FT-817 -- which I love. What are good antenna ideas for portable operation, i.e. from a motel room. Would like to work 40-meters and perhaps higher frequencies.

Thanks! joel / N5LXI
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WB6BYU
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Posts: 13017




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« Reply #1 on: February 22, 2001, 04:33:03 PM »

If you are going to limit yourself to inside the motel room, that
doesn't leave many options.  I have tried a dipole across the room,
but with limited success.  I would suggest a table-top loop: try
http://www.qsl.net/7n3wvm/mag-loop.html

I've had good luck with a dipole kit used outdoors.  This has 25'
of RG-174 coax and dipole wires for all bands.  The center insulator
is attached to the coax, and has thumb nuts for attaching whatever
set of wires I want to set up in any particular situation.  (This was
developed for backpacking - you may want to use 50' of RG-58
instead, if weight and size are not limitations.)  This gives you lots
of possibilities - I've used the 40m dipole wires as full wave loops
on 10m, and, in one case, combined the 40 and 80m dipole wires
as an open wire feedline for a 20m dipole strung off the edge of
a 300' cliff.

The other standard approach is the end-fed wire and a tuner.  The
best ground connection I've found is an aluminum window frame,
but many of the newer buildings are going to vinyl windows.
You may be able to hang the wire down from the window, throw it
over the roof, or tie it between buildings.  #22 stranded, insulated
wire is good - try grey or black if you expect to operate mostly
in the evenings.
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WB2WIK
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Posts: 20542




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« Reply #2 on: February 27, 2001, 01:38:05 PM »

Dale has great suggestions.  If you prefer just buying something and not experimenting with homebrewing portable antennas, I've actually had pretty good luck with the B&W AP-10 portable clamp-on whip, which comes with loading coils for the HF bands and a wire counterpoise that can be adjusted to an effective length and thrown just about anywhere.  I've used this antenna, clamped to window frames of hotel/motel rooms all over the world, and been pretty surprised at how well it's worked.  Since I operate mostly CW, this does make "getting out" a bit easier...CW is at least 10 dB more effective than SSB, no matter how you slice it.  Problem with many hotel rooms, especially the big high-rises, is that often the windows don't open at all.  This is definitely true of most of the mammoth hotels in Las Vegas!  One reason I prefer the drive-up motel type accommodations...not only are they easier to get into and out of when you move around a lot, but they have windows that open!  Good hotel room DXing!  Steve WB2WIK/6
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KD5IVP
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Posts: 22




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« Reply #3 on: June 30, 2001, 11:10:44 PM »

I've run all sorts of minimalist antennas for QRP and always come back to
the 1/2 wave wire with a 1/4 wave counterpoise.  This settup nets great success in
hotel rooms as well as mountain tops.  I built a tiny (1/2 the size of an Altoids tin)
L- network from a polyvaricon cap out of a cheap transistor radio and a 39 cent coil form
with a ferrite tunning slug.  This will easily handle your 5 watts.  My 20 meter antenna
and conterpoise will reel up in one of those Radio Shack "portable short wave listening antenna"
reels.  Throw away the wire that comes on it and wind on 33 ft. of 24 ga. wire and another
17 ft. for the counterpoise.  Use the little suction cups you get with radar detectors, and
a close pin or two to stick the antenna wire around the hotel room.  I've only run a watt with my rigs.
Your 5 watts should be easy stuff!
Paul, KD5IVP
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VK2DMH
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Posts: 14




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« Reply #4 on: July 03, 2001, 09:26:27 AM »

Take a look at the Minibac antenna idea from Bonnie Crystal KQ6XA. http://www.qsl.net/kq6xa/antenna/

Bonnie is very active in three Yahoo groups that I subscribe to: HFPACK FT-817 and FT817 (no hyphen) where lots of testing and discussion occurs about low power and portable antennas. (Go to http://groups.yahoo.com, sign in and join. I sugest you ask for a digest of the messages to be sent to you once a day. There are also files and photos on the group sites.)
   There has also been a lot of info on working from hotel rooms. (Sorry I can't say which of the 3 groups it was in.) But the finding was that most big modern hotels have tiny particles of lead in their window glass, and that stops most radio waves from getting through... One of the tricks to get past this is to use an ATU and screw/clamp your antenna connection to the metal window frame itself, and the counterpoise to the ground/earth pin of the nearest powerplug.
   There is a whole heap of work going on on what works best, but if you have the space to erect it a dipole (coax feed) or a doublet (twin wire feed) will give the best signal. Bonnie's Minibac can be used as a doublet, an inverted L and several other configurations.
   There are a few small antennas available for the FT-817, the Watson ATX Walkabout portable 80m-6m http://www.wsplc.com/products.html, the Super Antennas MP-1 http://www.superantennas.com/ and a Canadian "Miracle Whip" http://www.miracleantenna.com/products.htm (which nobody has tried yet because it is so new). But concencus is that anything small is going to be pretty difficult to be heard on, remembering you are QRP in the first place.
   Those who have them swear by the LDG Electronics Z-11 auto=tuner,
http://www.ldgelectronics.com/z-11.html
or the Emtech ZM-2 http://emtech.steadynet.com/zmdesc.htm
-- the only problem is that you have to build these kits!
73 de vk2dmh, David Harvey
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N8MHD
Member

Posts: 11




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« Reply #5 on: July 13, 2001, 12:15:21 PM »

Looking at the KQ6XA minibac -- she says it's possible to connect the twin lead directly to a bnc connector, and plug it into an unbalanced transmitter output.  What's the effect of this?  It seems to me that if it worked, everyone would be doing it because it eliminates the loss from the balun.

Specifically, what happens if you connect twin lead directly to the output of a K1 with the auto antenna tuner?
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G4AON
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Posts: 516




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« Reply #6 on: August 05, 2001, 11:25:10 AM »

If you don't mind installing your antenna away from the hotel building (if that's possible), then a portable "fishing pole" mast might be a great help.

I've recently bought a DK9SQ 10 metre (33 foot) telescopic mast that's based on a fishing pole. The mast collapses down inside itself, is 1.25 metres (4 foot) long collapsed and weighs 1.5 Kg. You will need to support the mast in some way, maybe using three string "guys".

The "full size" dipole and ground plane antennas will always outperform the hand portable HF whip and window clip whip antennas.

No doubt you will need to pick hotels in the more rural areas to take advantage of working DX with reasonable sized antennas!

Dave, G4AON
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