Our winter weather may have a few weeks to run yet, but a relatively warm spell gave me the opportunity to get out into the Big Blue Sky Shack to try out another antenna idea. Destination: MacGregor Point Provincial Park on the Ontario shore of mighty Lake Huron. The shore ice still stretched quite a long way out onto the lake in the direction of Michigan, about 100 miles away and a cold wind was blowing in off the lake. Not perfect weather for outdoor operations – but good enough.
Purpose: to find out whether a simple idea could turn a humble vertical whip antenna into something more versatile. Could this be used as a directional antenna to focus a signal into a desired target area? Could it even be used as a cloud burner to shoot a Near Vertical Incidence Skywave (NVIS) signal straight up to the F2 layer for strong local coverage? I decided to find out.
The antenna was actually not quite a simple vertical, but close. It was the Ham Radio Outside the Box Coil-Loaded End-Fed Half-Wave (CLEFHW). Its advantage over a quarter-wave vertical is that no separate counterpoise wire is required – just a short length (about 18 inches) of coax terminated in a 1:1 unun.
This was also the first outing for a new ham-made radio backpack. The radio is a QRP Labs QMX (low band), built into a steel 30cal ammo box along with a Talentcell 3000mAh Li-Ion battery, Drox buck converter (to keep the voltage down to 12 volts – the QMX gets unhappy with excessive supply voltage). The Putikeeg paddle key has strong magnets on its base that lock it into place on the steel ammo box which keeps my keying from getting too erratic!
A second identical ammo box sits below the first one and contains all the spare parts that might be needed during an outdoor ops session (standby battery, spare cables, connectors etc).
Both boxes sit on a custom aluminum frame, secured by 1-inch webbing straps. The whole pack is carried by means of a set of 2-inch webbing shoulder and waist straps. In use the radio and key sit at just the right height when the operator is perched on a camping stool so no table is needed.
Why the military look?
Well, a couple of reasons there. First, I actually like the appearance of military style radio gear. Probably nostalgia because I was first introduced to ham radio in the 1960s and the first “amateur” radio I saw was a converted WW2 surplus No.19 Wireless Set. But second, and more importantly, the military and I have similar objectives – we both need rugged gear that can withstand the rigors of rough handling out in the field. Snow, mud, wind and rain all be damned – comms must continue regardless <smile>.
The canvas parachute bag at the front contains a selection of coax cables, as well as other wire antenna options.
The radio box at the top can be sealed by replacing the detachable lid. It has a rubber gasket to keep out the elements when the radio is not in use.
The radio box can be removed from the pack frame quickly and easily. I keep a wire bail for picnic table operation, although that luxury is a rare occurrence for me.
Orienting the antenna
The whip and loading coil are attached to the pack frame by means of an aluminum bracket with a 3/8×24 to SO-239 adapter. I wish they made a 3/8×24 to BNC adapter; instead I made up a short cable with a PL-259 on one end and a BNC on the other.
The bracket is the secret to the antenna’s versatility. As you can see in the picture, the pack frame has curved shoulders. By mounting the bracket on the straight portion of the pack frame, the whip remains vertical and vertical whip antennas have an omnidirectional radiation pattern.
Now, if the bracket is mounted on the curved shoulder of the pack frame the whip becomes oriented at an angle. As we shall explore in a moment, this creates a major lobe in the radiation pattern in a direction away from where the whip is pointing.
But doesn’t the weight of a leaning 18.5ft whip cause the whole pack to topple? Actually no. It was discovered that the weight of the two steel ammo boxes and contents are sufficient to counteract any potential gravitational instability. In fact during the field trial on the shore of Lake Huron the whole pack remained entirely stable, which is vital for this operator who cannot operate a set of paddles properly unless they are very securely mounted.
It is not necessary to set the antenna bracket too high on the curve of the pack frame because the whip itself is quite flexible which enhances the lean angle.
To operate in NVIS mode all we have to do is raise the bracket a little higher on the curve of the pack frame so that the top section of the whip lays almost horizontal a few feet above the ground. This method has been used on vehicles by the military so I have to credit them as the originator of the idea. It probably won’t perform as well as a low dipole, but it benefits from being self-supporting and quick to deploy.
How did the directional antenna perform?
The Huron shore trial tested the directional properties of the antenna. The wind coming off the lake was a little too cold for a long operating session and besides I had to find a small corner of the operating area that was sheltered and clear of snow and the vast expanse of thick mud created by the early spring thaw. So, the test was focused on checking the performance of the whip oriented as a sloper. A sloper is a simple, well-established way of getting directionality out of an antenna, but is usually achieved with a wire antenna. This unique version of that method gets the same effect with an entirely self-contained whip antenna in a rapid deployment portable radio pack.
A simple antenna such as this could not be expected to rival a Yagi-Uda beam but it does exhibit a very pronounced directional radiation pattern as EZNEC reveals in detail.
The elevation pattern shows a strong low angle lobe in the direction opposite to the lean of the whip. This should produce good DX results when the propagation conditions are favorable.
If we look at the azimuth propagation we can see that it is almost omnidirectional at low angles. The front/back is only about 2dB which is less than half an S-unit.
The real power of this antenna orientation can be seen when we examine the azimuth propagation at higher angles. In the third image we can see the radiation pattern at 60 degrees elevation. The front/back is now at around 13dB which is approximately 2 S-units.
60 degrees elevation is almost in NVIS territory and should provide excellent propagation over quite a wide area.
NB: For simplicity, these results were modeled using a full-length EFHW on 20m. If anybody wishes to model the exact configuration please note that the base loading coil is 6.6 microhenries and the whip is 18.5ft long. I chose not to go this route because the curve of a sloping telescopic whip is unpredictable (especially in the wind).
Could a puny 3.5 watt signal into a compromised whip antenna cut the mustard? On the principle that you can work DX with a wet noodle on the right day, then yes. Propagation conditions were moderate with a K-index of 3 on the day of the trial, but among my other contacts I did work a station in North Dakota (from my QTH is southern Ontario). That’s a distance of a little less than 2000km; not outstanding but encouraging.
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