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Another Approach to Hidden HF Antennas

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ANTENTOP- 01- 2017 # 021

Another Approach to Hidden HF Antennas



Notice that, at 10 to 25 degrees, the ground reflection is very weak. It also is shifted 90 degrees in phase from the incident ray. Therefore, radiation from the grasswire, off the ends will be about the same as if the ground were not present.

But launching a ray at, say, 15 to 20 degrees takeoff angle, in a direction toward Europe, can be useful! That's what a grasswire does. It is lossy in all directions, but least lossy when exciting the ionosphere for a long-haul DX contact. To demonstrate the point, here's an extract of K3MT's log, for October of 1988, (ahh, glory! Yes, the SSN was good then!) using a grasswire!

Not bad, for a wire on the ground. Notice that contacts were made on 80, 40, 20, 15, and 10 meters. The signal reports are not fantastic.

But contacts were made, and ham radio was enjoyed! Five countries were worked in 3 days. And the best part of this setup: the neighbors never knew that a ham station was on the air!

During our Bermuda excursion, I took a TR-7, small antenna tuner, a power supply, and a Grasswire.  We were guests of a small family-run group of rental cottages in Southampton for four days.  On the third day, one of the elder family members chatted with me a bit, and asked if I was perhaps a radio amateur.


I said, “yes.”  In fact, I had been on the air for the previous two days, using a Grasswire.  It was only that morning that he, in cleaning up around the area, came across the antenna!  That’s a low-profile antenna.   



GMT     CALL    his/my RST    FREQ    Power




1554   SM6DYK    579 / 559   28004     80

1601   SM0LBR    569 / 439   21007    100     RAY - STOCKHOLM

2001   W4JBQ     579 / 569    7029     40     JOE - FT WRIGHT, KY

2141   W8LNJ     579 / 459   28015     80     DAVE - DALLAS, TX




0227   W8AO      589 / 569    3547     15     BOB - SILVER LAKE, OH

1720   G3RFE     579 / 559   21016    100     TOM - BARROW

1932   G0CBW     569 / 559   14029     50     MEL

1945   VE2FOU    589 / 559    7032    100     ANDRE - IBERVILLE

2026   KB7UX     569 / 539   21040    100     RUSS - CHINO VALLEY, AZ

2100   I2JIN     589 / 559   14022     40     BOB - COMO

2123   G3JVC     569 / 559   14022     40     JOHN - LONDON




2105   WA200JXT  599 / 599   28015     80     ND



Feeding the Grasswire


Since this antenna is largely resistive, a simple trifilar balun is all that I have ever had to use. Figure 4 shows how to make a Balun that works.


Typically I pull the insulated jacket off some indoor telephone wiring cable.  Four insulated #22 copper wires are inside:  discard one of these and use the remaining three. 


Wind about 16 turns on a T-200-2 core (available from Amidon and others), without allowing the wire to twist (keep the three conductors parallel at all times.)


Notice that this "balun" really matches an unbalanced antenna to an unbalanced transmission line.  It is basically a wide-band, three-winding autotransformer.  Impedance ratios are as shown on the drawing.  Generally it is necessary to connect the coax to either A2/B1 or B2/C1, and the antenna to B2/C1 or to C2. This may change from one band to another, and usually does.

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Last Updated:

February 25, 2018 22:25