- On a vehicle with a steel body and roof, the most feasible 2 meter slot antenna design is a pair of square flat plates with spacers to maintain the space between them. The slot ends up being the horizontal space between the plates.
- The skeleton slot provide an ingenious to feed two stack yagi antennas her is my design.
- Two Meter Antenna. It's likely your first Ham radio purchase was a 2 meter or dual-band HT. Unfortunately, the rubber duck antenna that came with it isn't the best choice for maximum signal. If you're tired of people telling you your signal is weak, the simplest remedy is an improved antenna.
I am always interested in trying different antenna designs, especially if they are simple to construct and provide increased functionality. While perusing some old issues of QST magazine online I found a series of articles that discuss a design called the Folded Skeleton Sleeve. The design is a unique way to build a dual-band resonant dipole or groundplane vertical. The articles appear in the May 2011, October 2011, October 2012, December 2013, and March 2015 issues of QST magazine.
I was particularly interested in this antenna design because a simple resonant dual-band antenna could be very useful for deployment at Field Day or for EMCOMM purposes. Other multi-band antenna designs exist and can perform quite well (windoms, off-center-fed dipoles, G5RVs, non resonant end feds, dipoles fed with window line, etc.), however, most of these require a wide range antenna tuner to achieve a decent SWR on multiple bands. Other designs, such as trap dipoles, can be heavy and cumbersome with multiple points of failure. The folded skeleton sleeve design exhibits non of these limitations.
Design
Showed me a skeleton-slot antenna for 440 MHz. G6JP ex-plains '.further experiments showed that a thin rod bent to di-mensions of 5λ/8 by 5λ/24 exhibited similar properties of a true magnetic dipole slot'. See skeleton slot on left side of Fig 7. Figure 7 – Skeleton-Slot element can be used as a driv.
The folded skeleton sleeve at first looks like a standard folded dipole, however, the top radiator is not continuous. Two notches are cut along the top of the window line to create the parasitic element that allows for operation on the higher frequency band.
A 75M / 40M antenna should be perfect for both EMCOMM (these are the most common HF bands used for emergency communications) and Field Day. A 40M / 20M antenna is equally perfect for Field Day and the combination of the two provides a lot of operating versatility from two simple antennas that cover the three busiest Field Day bands. I also decided to construct a 40M / 30M antenna for use as a portable antenna for digital communications.
Construction
I built the antennas using 18AWG stranded copper-weld 450 Ohm window line (Wireman #553) and folded dipole insulator kits (Wireman #804) which make fantastic strain reliefs for securing the window line. I also made my own 1:1 baluns in a similar design to what I have done before, except this time I used FT-150A-K toroids and 18AWG wire which allowed me to make the baluns smaller in size while still being adequate to handle 100W. To house the baluns I used Bud Industries PN-1322-DGMB NEMA 4X enclosures. These are well made boxes and they feature convenient mounting tabs that are easily bolted to the center insulator.
75/40 Bandwidth
75 Meter Band
- 2:1 SWR: 3.68-3.785
- 3:1 SWR: 3.63-3.86
40 Meter Band
- 2:1 SWR: 7.18-7.238
- 3:1 SWR: 7.1-7.3
While the bandwidth of this antenna is not particularly wide, it is easily matched to the radio's 50 ohm output with practically any antenna tuner.
My ham radio club used the 75/40 at our Field Day site for the duration of the event. While obviously intended for use on 75 & 40 meters, the antenna was used on the higher bands as well with the help of a wide range antenna tuner. Over the course of field day this setup resulted in over 350 CW contacts.
40/30 Bandwidth
40 Meter Band
- 2:1 SWR: 7.158-7.33
- 3:1 SWR: 7.073-7.448
Big bang theory casino episode. 30 Meter Band
- 2:1 SWR: 9.93-10.24
This antenna exhibits better bandwidth than the 75/40 and even reaches an SWR of 1.1:1 on 30 meters.
40/20 Bandwidth
This antenna is by far the best design of the bunch. This configuration results in an SWR of under 2:1 across the entirety of both the 40 and 20 meter bands.
Antenna Winders
Since ladder line can be annoying to work with since it doesn't coil easily, I decided to build some winders from 1/2 inch PVC pipe to keep the finished antennas organized. I built a larger one for the 75/40 antenna and smaller ones for the 40/20 and 40/30 antennas. I am really pleased with how these turned out and plan to build more for use with other antennas; they are a fantastic way to avoid a tangled mess.
2 Meter Skeleton Slot Antenna Tuner
Anyone ever heard of J-BEAM or SLOT-BEAM Yagi antenna's?I have one here, it's quite an oldie. The one I've got is a 18 element
(including driver and reflector) for 70 cm. The driver looks lika a kind of
'stacked folded dipole':
+------------------------+
| |
+--------o o---------+
| |
+------------------------+
The two 'dipoles' are not 180 degrees but slightly less:
O
O
/
/
O
2 Meter Skeleton Slot Antenna Receiver
The reflector is similar shape as the driver, but both 'dipoles' are in a
straight line (180 degrees).
O
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|
O
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|
O
Strange things are: all the directors are of the same length and the width
is bigger than the dipole/reflector width. The dipoles seem a bit small
comparing to a ordinary folded 70 cm dipole. At first I thought it was an
antenna for higher frequencies, but the guy I bought it from ensures me he
used it several years for 70 cm (I believe him! He's a nice guy and I got
the stuff for 'an apple and an egg' so why should he lie?). I don't know
exactly what kind of balun I should provide this beauty with? It's got a
balun inside but it's a bit rosty so want to replace it by a new one.
I cleaned the aluminum (it's nice and shiny now, like new). It's a very
impressive antenna. but does it WORK? Anyone got any info on it while I'm
working at the 3-meter-boom-beast?
Please reply ONLY via email to: PD1..@AMSAT.ORG
2 Meter Skeleton Slot Antenna Combo
73, Pleun
P.S. (Dutch): Dit bericht was in het Engels omdat ik het ook in andere
internationale newsgroepen heb gepost. Als iemand informatie heeft over de
J-beam of Slot-beam en het bericht niet helemaal begrijpt dan wil ik gerust
even een vertalingkje sturen.
2 Meter Skeleton Slot Antenna Mounts
