On 19 Mar 2006 19:01:25 -0800, "RHF"
wrote:

How...,

1. For a dipole skip the 4:1 balun - go straight to the coax
-R- Good advise for a Ham using the Dipole for a Specific
Amateur Radio Meter Band - But for a Shortwave Listener
(SWL) who is trying to use the Dipole as a general Antenna
for All-SWL-Band reception the 4:1 Balun gives them more
Listening-ability-across-the-Bands.
REMEMBER - This is a Three Band : 49 & 31 & 22 Meter
Bands Shortwave Listener (SWL) "Receive Only" Tri-Band
Dipole {Wire} Antenna built on a On-the-Fence
I believe you are mis-applying the balun. A dipole has an inherent
impedance of around 70 ohms - if using 50 ohm coax you could use a
1.5:1 or call it close enough and use a 1:1 balun (which I previously
mis-stated as an unun) - or just go direct to the coax. As to giving
'more listenability' on other bands, well that's probably about as
debated as the 9:1 balun with end-fed wires & inverted L antennas.
One thing the balun does do is provide isolation between the antenna
and feedline and this 'decoupling' can make for a quiter antenna
system.

2. or use a 1:1 unun.
-R- An UnUn with a Dipole ?
- - - Dipole to Twin Lead / Ladder Line = BalBal
- - - Dipole to Coax Cable = BalUn
OOPS! My faux pas, should read 1:1 balun for Dipole to 75 ohm coax
cable, 1.5:1 balun for Dipole to 50 ohm coax cable. Dipole to
twinlead could be direct or use a 1:1 isolation transformer.

3. If you were building a folded dipole the 4:1 balun
would be more appropriate.
-R- Again this is a Three Band : 49 & 31 & 22 Meter
Bands Shortwave Listener (SWL) "Receive Only"
Tri-Band Dipole {Wire} Antenna built on a On-the-Fence
The object of the 4:1 Balun is to intergrate the Signals
developed by the Three Dipole Antenna Elements into
the Single Coax Cable Feed-in-Line and provide better
Across-the-Shortwave-Bands frequency coverage.
The balun will not necessarily 'integrate the signals', in other than
a 1:1 configuration it transforms impedance and allows you to go from
balanced to unbalanced line. At some frequencies it may 'smooth out'
the impedance mismatch, however if you want to combine the signals a
triplexer would do the trick.

4. You can ground or not ground the dipole;
it is a balanced antenna so grounding is a
matter of lightning protection & providing a
path for the static electricity to drain
- a better path than draining to the radio.
-R- Lightning Protection and a Static Electricity
'drain' Path are always two good things to achieve
with any Shortwave Listener's (SWL) Antenna.
Agreed.

5. I guess the dipole that's 1 foot above the
ground is for 'ground wave' reception 8-}
-R- Wave Goodbye "How..."
Nope, not goodbye yet.......I'd like to rebut your rebuttal.......

FWIW - A Dipole On-the-Fence would not be my first
choice as a Shortwave Listener's (SWL) Antenna.
But what can you do - If the ONLY place that you can
build an Antenna is On-the-Fence ? ? ? and you don't
have the Money for a Wellbrook Loop Antenna ? ? ?
Plus someone has convinced you that the ONLY
Antenna that is worth having is a Dipole - because it
is a complete Antenna that does not require a ground
to work. - - - So now all you know is that you have to
build a Dipole Antenna and it's got to fit On-the-Fence [.]


right now i am beginning to feel a little di-pole-er - iane ~ RHF
.
RHF - Granted, a fence mounted antenna is the best some folks can do;
there are other options to the dipole such as an end-fed or a
fence-loop; the former requiring a ground the latter not. Might I
suggest to you the ARRL Antenna Book (not the end-all to antenna
knowledge but a good start; it has a section on coupling the antenna
to the feedline. They explain what I was trying to say in my original
response to you in a better fashion than I can. They even describe a
1:1 balun which is what I mis-stated as an unun. Though you (and many
participants here) are mainly interested in receive-only antennas; the
principles apply equally to antennas used for transmit and receive.
If you don't have a current copy of this ARRL publication see if you
can get your hands on a used one - the physics haven't changed from
year to year. What you have described will work, no doubt about it -
but wouldn't you like to explore ways to make things work better?

Howard