Heathkit box + more

[Stephen C. Finch]

Martin,

IMO using a balun is always advisable when transmitting from a dipole.  If
the dipole is flat, then the theoretical impedance is 72 ohms.  If the legs
slope, the impedance will decrease with 90 to 120 degrees between the legs
giving 50- ohms or so.  So for impedance matching, no balun would be
necessary.

However, if a coax is attached directly to a dipole, it is more common than
not that currents will flow in the outer jacket to the coax due to the
mismatch between the dipole and the antenna.  These currents several affect
the antenna pattern and cause the SWR to go "haywire." This is primarily due
to the fact that a dipole is a balanced antenna and the coax is an
unbalanced transmission line.  Thus the balun  ("bal"anced to "un" balanced)
will transform the balanced dipole to the unbalanced coax.

There are two types of baluns - current and voltage.  I prefer the current
baluns as they are constructed to eliminate the outer-shield currents.  Two
good books are very insightful into this topic:  "Reflections II" by M.
Walter Maxwell and "Building and Using Baluns and Ununs" by Jerry Sevik.
Both are terrific additions to a ham's library.  I especially like
Reflections II as it describes and debunks many antenna, transmissions line,
and antenna tuner myths.

Steve Finch
AIØW

-----Original Message-----
From: Heathkit Owners and Collectors List [mailto:HEATH at LISTSERV.TEMPE.GOV]
On Behalf Of George R. Griesbach W5GRG
Sent: Saturday, December 25, 2004 8:01 PM
To: HEATH at LISTSERV.TEMPE.GOV
Subject: FS: Heathkit box + more

 I was rummaging around in a shop I frequent and found a large Heathkit box
approx 24x24x12h. No Heathkit inside, but there was a complete G scale Emmit
Kelly Circus Train set by Bachman, steam locomotive+tender+ 3 cars+ track
and PS and misc acc.  I set it up under my tree, runs great. I will put it
all back in the box and sell all for $150.00+ shipping from 78013.
I also have some other Heathkit stuff on my website FS.
pics
http://www.comforttexas.net/gallery
Thank You
George R. Griesbach W5GRG
505 River Oaks Rd.
Comfort, Texas 78013
w5grg at comforttexas.net
http://www.comforttexas.net/w5grg
---
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