Re: 40-meter Loop

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From: David D. Meacham (ddm@datatamers.com)
Date: Fri Nov 29 1996 - 12:43:34 EST


Hi Bob,

My only antenna for 40 meters is a 40-meter Delta Loop. Its a
great antenna for DX (low angle of radiation) IF you feed it so the
polarization is vertical. The apex on mine is about 37 feet above ground.
The horizontal portion is 7 feet above ground. Overall length about 143
feet. It needs only one support in this configuration. Feed it in a lower
corner, or, as I do, 1/4-wavelength down from the apex. Feed impedance is
about 115 Ohms. Use open-wire line to a balanced tuner. I use 72-Ohm
transmitting Twinlead an electrical 1/2-wavelength long to the tuner.
If fed in a corner you can use 1/4-wavelength of 75-Ohm coax, then any
length of 50-Ohm coax to shack (this scheme for one band only).

Another, slightly better configuration is to invert the delta so the
horizontal portion is high in the air and the point is near the ground.
Radiation angle is lower still. Feed at a corner high in the air, or even
better, 1/4-wavelength UP from the point near the ground. For this one
use ONLY balanced line (open wire, Twinlead, etc.). Impedance will be a
little higher, say 125 Ohms. Needs two support points. Cud be like:
      * * * *
   * * * *
  * *---*-------------------------*----* *
  * * \ / * *
    * * \ / * *
       * \ / *
       * \ / *
       * \ / *
       * \ / *
       * \/ *
       * *
_______*_______________________________________________*___________________
 

 Anyway, you get the idea!

If you want two bands you could nest the 30-meter loop inside the 40 and
feed them separately.

With a balanced tuner you can easily cover the whole 40-meter band.

If you use the 1/4-wave 75-Ohm transformer of coax be sure to cut the
coax shorter than an electrical 1/4 wave by the velocity factor of the
coax (about 0.66 times electrical length in space).

Max lobe is broadside (bidirectional). Off the sides, signal is about 3dB
down. Main lobes are broad (beamwidth).

For a simple DX antenna for 40 or 30 I don't think you can beat the Delta
Loop.

72, es gud luck, Dave, W6EMD

p.s. I'll try to dig up another bit of loop info. I sent both to AL7FS
some time ago.


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