[QRP] Usable, accessible portable antenna?

[Bob Nielsen]

On Sat, Apr 10, 2004 at 11:23:50PM -0700, Daniel Reynolds wrote:

> I live in an apartment. What I've been trying lately is an 85 foot end fed long
> wire with a 15 foot counterpoise attached directly to the balun which is hooked
> up right to the output of my K2 (which has the tuner option included). If the
> IC-703 tuner can handle most SWR's, the Balun will further improve its ability.
> Most baluns can be had for around $30 or more. I've been using 22 gauge wire
> for temporary antennas strung from my 2nd story balcony and tied off to a fence
> 85 feet away (the counterpoise just droops over the balcony).


A balun is intended for use between a balanced antennas and an
unbalanced transmitter output.  With an unbalanced antenna like your
end-fed wire, it won't help the match and could introduce additional
loss into the system.  A K2 or IC-703 tuner should be able to match it
over a wide range of frequencies (you may encounter problems at some
frequencies, however).

When I lived in AZ, I had a ~60 foot length of wire which I ran through
a window and under the roof overhang.  It worked fairly well with my
DSW-40 and ZM-1 Z-match tuner.  On 20 meters, however, it was lousy. 
Where I live now, I don't have any restrictions and have put up a
multiband vertical, which of course is a big improvement.  I bought a
MP-1 for travelling, but haven't had an opportunity to use it yet.


 
> The key for compromise antennas like the Buddipole is to get a low SWR by
> tuning the antenna, NOT by using an antenna tuner in your radio. The tuner in
> the radio only makes the transmitter happy - it doesn't make the antenna more
> efficient.
> 
> However, using the same tuner into a less-of-a-compromise antenna like a long
> wire actually has a positive effect since it enables the radio to transfer more
> power into a mismatched load (Although - I'm sure those who are more technical
> will set me straight if I need correction).

That is because solid-state radios will reduce the output power when
they see a large (typically > 2:1) mismatch.  Back when I had tube
transmitters this wasn't a problem.


> 
> If you have a good idea of your surroundings, or if you have another ham who is
> experienced with stealth antennas, you will hopefully be able to determine just
> how high you can get a wire. The higher you can get it (for example, 30-40 feet
> up), the better chance you will have of getting your QRP signal off the
> continent on bands like 20-15m. If you run a random length wire along a wooden
> fence line which is less than 10 feet tall - it may tune up on all the bands,
> but your contacts will be relegated to primarily stateside contacts on bands
> like 20-15m, and states in your region on 80-30m. That's because the closer
> your wire is to the ground, the more of the signal that goes up (instead of out
> ward and low to the horizon).


Before I put up my vertical, I strung a temporary wire antenna which
was about 100 ft. long, L-shaped.  It was just above the peak of my
roof (about 16 feet) I fed it at the corner of the "L" with coax (about
20 ft).  The internal tuner of my TS-570 wouldn't match it on some
bands, so I used an external tuner.  I was able to quite a bit of DX at
QRP levels with this arrangement.

Darrell, if there is any way you can get an external antenna installed
(even stealth), it would probably be an improvement over the outbacker
(which is fine for portable use, however).

73, Bob N7XY

-- 
Bob Nielsen, N7XY                          n7xy (at) n7xy.net
Bainbridge Island, WA                      http://www.n7xy.net