Dipole advise WTD
JEFF UK
I want to put up a receiving dipole for 0 - 30 mhz SWL.
I have a roll of 75 ohm tv coax.
Loads of stranded 2.5mm copper insulated electrical cable.
Questions;
What length should i cut the dipole for general 0 - 30 mhz listening ?
I will need to fold both ends to fit into my narrow garden .. is this ok ?
Do i need any form of earthling to the coax feed ?
Do i need a balun.. if so which and how do i build one ?
Thank you.
All advise appreciated
Jeff
RHF
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JEFF UK,
The Dipole Antenna is usually used as a Frequency Specific and
when properly installed Directional Antenna. The Dipole is great
if you are an Amateur/HAM who is Transmitting and Receiving on a
HAM Band and its multiples: 160M > 80M > 40 > 20 > 10M. If you
are a Shortwave Listener "SWL" that is looking to catch all
signals from all directions. The the Dipole would not be your
Antenna of choice.
In the same space your better SWL Antenna is the WINDOM Antenna.
Looks like an Off-Center Fed Dipole Antenna and offers more
broad band characteristic then the Dipole.
READ - Windom -vice- Dipole which is the better SWL Antenna ? ? ?
http://groups.yahoo.com/group/SWL-AM-FM-Antenna/message/80
FWIW - Think of the WINDOM Antenna as an OFF-Center (36%/64%) Feed
Dipole that is more Broad Banded (not as frequency specific and
resonant) and more omni-directional (not as bi-directional) as the
common Dipole Antenna.
IMHO - For a SWL Antenna the WINDOM Antenna is the better "All Band"
'All Directions' Antenna choice over the common Dipole Antenna.
READ - Off-Center Fed Random Wire Antenna - Hey It's a Windom !
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1677
READ - The 'right' Matching Transformer for your 'type' of Windom Antenna
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1596
This Message takes about "Sizing" of your Windom Antenna.
TIP #1 - The 'basic' Flat Top Windom for Shortwave Listening:
For Shortwave Listing I 'like' the Dipole 'configured' type
Windom with a 300 Ohm Twin Lead or 450 Ohm Ladder Line Vertical
Feed-in-Line. If you have between 65 to 80 Feet of 'available'
Space for your Antenna try:
* Cut the Long-Arm of the Windom Antenna for the 49 Meter SW Band
= Long-Arm's Length = 38.5 Feet
= Long-Arm (38.5) / Total Length (62.7) = 61.5%
* Cut the Short-Arm of the Windom Antenna for the 31 Meter SW Band
= Short-Arm's Length = 24.1 Feet
= Short-Arm (24.1) / Total Length (62.7) = 38.5%
Total Length of this Windom Antenna would be 62.7 Feet.
- Mount/Rig the Antenna at a Height of 24-26 Feet.
- Run the Ladder Line Straight Down Vertically to the Ground.
- Install a Ground Rod at this point in the Ground 'directly'
under the Ladder Line.
- Mount your Balun 'directly' on the Ground Rod.
- Run/Route your Coax Cable from the 'junction' of the Ground
Rod and Ladder Line and to your Radios/Receivers.
- Connect the Ground Rod/Wire; Ladder Line and Coax Cable to
the Balun.
TIP #2 - The Folded "Half-Square" Windom for Shortwave Listening:
The above Windom Antenna is "To Big" for your 'avaiable space'
consider Folding it at the ends into a Half-Square Windom.
Here is the 'simple' HOW TO:
- The Long-Arm's Length = 38.5 Feet is Bent from the Horizontal
at 19.25 Feet from the Off-Center Feed-Point and goes Vertically
Down for 19.25 Feet.
- The Short-Arm's Length = 24.1 Feet is Bent from the Horizontal
at 12.1 Feet from the Off-Center Feed-Point and goes Vertically
Down for 12 Feet.
- Mount/Rig the Antenna at a Height of 20-25 Feet.
- Run the Ladder Line Straight Down Vertically to the Ground.
- Install a Ground Rod at this point in the Ground 'directly'
under the Ladder Line.
- Mount your Balun 'directly' on the Ground Rod.
- Run/Route your Coax Cable from the 'junction' of the Ground
Rod and Ladder Line and to your Radios/Receivers.
- Connect the Ground Rod/Wire; Ladder Line and Coax Cable to
the Balun.
READ - Need an Off-Center Fed SWL Antenna consider a Windom type design
http://groups.yahoo.com/group/Shortwave-SWL-Antenna/message/1582
READ - History of the Windom Antenna from the Scottish Ham Portal
http://www.scotham.net
ENJOY - Broadcast Band Listening and Shortwave Listening :o)
iane ~ RHF
.
Some Say: On A Clear Day You Can See Forever.
http://groups.yahoo.com/group/SWL-AM-FM-Antenna/message/502
I BELIEVE: On A Clear Night...
You Can Hear Forever and Beyond - The BEYOND !
.
.
starman
Dipoles are not the preferred antenna for wideband coverage (0-30 Mhz).
Consider a properly grounded inverted-L antenna such as the one
discribed on the following website.
http://www.anarc.org/naswa/badx/antennas/low-noise_antenna.html
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J999w
9.8mhz), cut your wire to length ( length in ft = 468/mhz ), forget the balun
just solder it up, and try it out. get it up as high as you can.
There's no better method to learn about antennas than building them and seeing
what works and what doesn't.
:^]
GL,
jw
k9rzz
milwaukee