[CQ-Contest] delta loop question 80m

[Edward Sawyer]

I no longer do this at my current station but used to have an 80M delta loop (single) and did exactly what Tony suggests.  I used open wire - 450 Ohm line as the stub and I just had a shorting clip to short circuit the stub at the base of the delta loop for SSB and unclipped it for CW.  Vertically polarized exactly as Tony describes.  For 2:1 Bandwidth, I have never seen a way to use a delta loop from 3850 - 3500 vertically.  It might be possible horizontally but if so its only because the low height above ground is making it so ineffective for DX the impedance is broad.  Not a good way to achieve the desired results.

73

Ed  N1UR

-----Original Message-----
From: CQ-Contest [mailto:cq-contest-bounces at contesting.com] On Behalf Of Tony Brock-Fisher via CQ-Contest
Sent: Monday, July 29, 2019 8:47 AM
To: reflector cq-contest
Subject: Re: [CQ-Contest] delta loop question 80m

Darrel-

I have a pair of delta loops in a phased configuration. They are very effective. Here are my thoughts:

-There are two ways of feeding them which result in either horizontal or vertical polarization. For low-angle DX work you want the vertical polarization (unless you can put?? the loops up higher than a half wavelength above ground).

-For the vertical polarization, feed the equilateral triangle full wavelength of wire at a point 1/4 wavelength down from the apex, near a corner.

-For vertical polarization, the loops need not be very high off the ground. The base leg of mine are only about 6-10 feet off the ground.

-An advantage is that this gives you?? a vertically polarized antenna that needs no ground radials! The base leg acts as a radial.

-The natural resonant impedance of a single full-wave loop is around 100 ohms. Use a 1/4 wavelength (electrical) of 75 ohm coax to match to 50 ohms.

-You asked about bandwidth. In any given configuration, 2:1 SWR bandwidth is NOT large enough to cover both phone and CW. Pick one.

-Seeing as you posted this to the CQ-Contest forum, I'll give you the contesting answer to tuning:

 ?????? Tune the loops for phone. Then when a CW contest comes along, walk out to your back yard and add about a 13' stub to the middle of the base leg. This is easily accessible from the ground. This stub is run at 90 degrees to the base leg and parallel to the ground. It will tune the loop down to the CW band. If you want to get clever it could be done with a vacuum relay.


Enjoy!

-Tony, K1KP

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