A delta loop antenna is not particularly suitable for SOTA. It requires much more space than a vertical and the set-up is more complicated.
Nevertheless I’d like to show this design here because sometimes space (and weight) don’t matter and a low take off angle is welcome. One possible scenario could be the VK/ZL/JA <> EU S2S event.
While searching for an alternative to my Linked- Dipole I tripped over the posting of Pedro, CT1DBS, illustrating an end-fed half-wave (EFHW)- Dipole with Traps. Here is the Link to his article. With this design changing bands can be done in no time thaks to the traps. Lowering or modifying the antenna is no longer necessary.
This is what my equipment looks like after I started a programme to reduce the weight (s. the 2 kg Challenge). I’m going to use it on long hikes and trips to high summits where weight comes into play.
From left to right: EFHW- Dipole with traps (40m, 30m, 20 m), 10m Nylon rope (red), tent peg, antenna bag, Unun 1:64, 1m RG58, bag for MTR 3B and Palm Pico Paddle, earplugs, 1250mAh LiPo battery 2S, power cable with fuse, 3 velcro straps, lashing belt, tape, writing board with log sheets, pencil, spare fuse, headlight, 3 x 10m guy rope with tent pegs, support plate 8mm (for guy wires), army knife, 6m fiberglass telescopic pole (57cm long).
The equipment as shown in the picture weighs 2067 grams. However, it is possible to leave the guy ropes out and attach the GRF pole to the summit cross using the lashing belt. Additionally, if a 1000mAh LiPo will be used instead of the 1250mAh LiPo, the total weight of my equipment is slightly above 1700 grams. This is 3 kg less than what I’m usually carrying around and definitely a big improvement.
On the trip to DL/AL-093 my rucksack was pretty heavy. Carrying all the things for an overnight stay in the alpine hut plus food & water plus radio & antennae added up to a total weight of more than 13 kg.
Back home I put everything from the KX3 to the pencil on the scales. The result was alarming: my SOTA- gear was weighing about 4700 grams! This is acceptable for trips to the low mountains but is definitely too much for higher summits and long hikes.
The top three contributors were:
Fiberglass pole (10m)
KX3 in Go- Box
Multiband Dipole with coax
A search for alternatives unfolded:
A lightweight 6m fiberglass pole is available but has a slight drawback: The usable height is only about 5 metres.
The MTR3B would significantly reduce the weight of a KX3 while only slightly reducing the operating comfort. It is possible to work on three bands. My signal would drop about 1 S- unit due to 6dB lower output power. This seems acceptable considering the reports I usually get.
An End Fed Half Wave Dipole (possibly with traps) appears to be a good alternative to the Multiband Dipole. Only a short piece of coax is required instead of 10 metres and – if mounted as inverted L – it has a lower footprint. A big bonus on a summit with restricted space. If built with traps, changing bands can be done in no time.
With these three measures the total weight of my SOTA- gear can be reduced by about 2.5kg without losing much performance.
The fiberglass- pole is already available and will replace the 10m Mast in the future.
A MTR3B Kit has been purchased. Assembly report is available here.
Antenna design hints for a Three Band EFHW Dipole can be found here.
Nachdem ich einige SOTA- Referenzen mit Monoband- Antennen aktiviert hatte, entstand der Wunsch nach einer Mehrbandantenne, denn der Bandwechsel war eine zeitraubende Angelegenheit. Die Antenne sollte mindestens die Bänder 40m, 30m und 20m abdecken, optional 15m. Der Umbau sollte nicht länger als drei Minuten dauern.
Die Idee stammt aus der CQ-DL 06/2014. Dort wurde ein Artikel mit dem Titel „Endgespeiste λ/2 Koaxantenne“ veröffentlicht. Beschrieben wird ein endgespeister Halbwellendipol, dessen Fußpunkt- Impedanz mittels Viertelwellentrafo in die Nähe von 50Ω gebracht wird.
Für den noch zu bauenden Mehrband- Dipol sollte eine Mantelwellensperre entworfen werden. Es gibt einen sehr guten Beitrag im Antennenbuch von HB9ACC. Leider ist das pdf im Moment nicht online verfügbar. Das ‚Transmission Line Transformers Handbook‚ von W2FMI in englischer Sprache ist ebenfalls sehr empfehlenswert.
From left to right: Folding stool, 2200mAh LiPo battery in a ’safe bag‘, throw bag (250g), 30m Nylon rope (3mm) , 2 x 10m Nylon rope (3mm) with tent pegs, KX3 with Palm Pico Paddle (on the KX3-Go-Box), 40m- and 30m- wire-dipole (w/o BALUN), 20m end-fed dipole, plywood board (serves as table), headlight, tape, writing board with log sheet, pencil, KX3 power cable with Power Pole plug, headphones, angle adapter BNC – UHF, Army knife, RG223 (20m), velcro straps, 3 x 10m guy rope with tent pegs, 10m fiberglass telescopic pole (67cm long), support plate 22mm (black, for guy wires), support plate 8mm with pulley block (blue, for antenna), 2 lashing belts.
As the trips are usually not tiring I don’t optimize the weight of the equipment more than necessary. I prefer a minimum of comfort (folding stool and plywood board) and the choice between several antennas and options to set them up: In a tree with throw bag and rope or on the fiberglass pole which can either be attached to a fence post or secured with guy- ropes.
The monoband antennas have been replaced with a linked dipole in the meantime. However, a further optimized antenna (End Fed Half Wave Dipole with Traps) is already under construction.
Having played with the KX3 for a couple of weeks I wanted to try it outdoor. But Hiking comprises some risk for the rig: rain and snow, shock and vibration and scratches from other things in the rucksack. The first attempt with bubble wrap worked but was not to my full satisfaction. A box was needed!
I searched the web for availalbe solutions (which are quite a few) and found Tom’s great Go Box: http://www.oe2atn.at/tom/gobox/ – the most professional one I found.
However, I had something different in mind: The box should look understated in order not to attract thieves on a long hike or a stay on a camping site. By accident I tripped over an empty first aid box. Slightly too big for the KX3 but apart from that very nice.
Old first aid box – used to store all kinds of stuff
Some pieces of foam were at hand and with a few cuts and a little bit of glue the protective padding was made.
The KX3, a short power cable and the Palm Pico Paddle fit nicely into the box.