Random-Wire Antenna with LDG RT-100

by Istvan Agg HA5CLF, N9EU

My Windom antenna happened to be damaged by human intervention since one of its legs, the shorter one, wire sloping down from the roof attached to a short pole on the fence was drastically pulled and bent. The longer part 27.4m (~90 ft) of the antenna remained intact.
Not having an antenna was not an option before the Christmas holidays. I decided to build a heavy-duty pole on the roof to be able to attach various antennas as needed in the future, but for now I built a random-wire antenna with a tuner at the antenna base.
This picture shows the roof and the possibilities to implement my antenna.

The chimney-like construction in front with the air-conditioning mounted on it is the access to the roof. It is on top of a round shaped stairway to the building. The rest of the roof is behind this with the chimney.
By regulations, it is forbidden to attach anything to the chimney, so I decided to attach my antenna pole to the roof access construct.

Figure-2: I purchased two of the above brackets to attach to the wall and hold the antenna pole.

The brick wall is 14cm (5 1/2 inches) thick, so it will hold the pole very firmly. I will be able to put various antennas on it in the future, such as a Gap Titan, but for now let’s talk about the Random-Wire LDG RT-100 remote tuned antenna erection.
Once I built the structure to hold the antenna, which consist of a 2.7m (~8 foot 10 inches) steel pipe, and a 4m (~13 foot) telescopic fibre pole purchased at the local fishing supplies store. The pole is actually 7m (~22 foot 11 inches) tall, but I removed the last 3 sections, since it is not firm enough to hold the antenna wire.
Next, I constructed the tuner assembly. Although the LDG TR-100 is a waterproof unit, I decided to protect it from the elements anyway. I purchased a Tupperware container large enough to hold the antenna tuner and a 1:9 balun.

Figure-3: Finally, after the assembly of the remote tuner box and the construction of the holding structure, here is the final look of the antenna.

Figure-4/5: A closer look at the tuner assembly and radials is shown next

There is an important aspect to random-wire antennas, and that is their critical lengths. Some critical lengths are impossible to tune on some of the bands. Mike, AB3AP posted a page: http://udel.edu/~mm/ham/randomWire that discusses random-wire antenna lengths to be avoided.
Since the remaining 27.4m (~90 ft) is exactly to be avoided, and luckily a piece of wire is still needed to bring down the wire from the top of the pole, it happens to be out of the critical length, but very close to it.
The next picture shows the antenna wire from the top of the roof of my condo to the top of the roof of a very friendly neighbour.


What are the results? Well, I conducted some limited tests. It tunes up fine from 80m to 10m bands. I also performed some tests with FT8. See the 80m and 40m band results.
This is 80m band in the evening for about 10 minutes of CQ-ing and making a few QSOs. The SFI was 82 and the k index 1.

This is 40m band in the evening for about 25 minutes of CQ-ing and making QSOs. The SFI and the k index was the same as above of course.

Now I just cross my finger that the winter elements will not damage the antenna. It is out of the reach of the frowning neighbours’ hands, but a harsh winter may also be destructive. I hope to meet you on the bands soon, but until then have a Merry Christmas and a Happy New Year. Let’s leave this 2020 behind and hope for a pandemic-free 2021.



    • Szervusz Andras, ugy nez ki meg van rajta egy kis munkam, meg fogom probalni egy 1:4 balunnal az 1:9 helyett. Sot egyenest balun nelkul is kiprobalom, hisz 4 es 800 ohm kozt tud hangolni. Egy verticalis antennanal, foleg ha eleg rovid, es az 5 meter alacsonyabb savokon az, a 4 ohm hasznos lehet. Neked is jo kiserletezest. 73 – Istvan

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