MTR3B – Kit Version

The MTR3B helps reducing the weight of my SOTA gear significantly. It weighs only about 15% of the KX3 in its Go- Box but has still acceptable output power and performance.

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DM/BW-078 – Roemerstein – 872m

Abstract

October 22, 2016: 13:40 – 14:40 UTC

Rig: KX3 / 10W, 2200mAh LiPo, Palm Pico Paddle
Ant: inverted V up 7m on a tree

9 CW QSOs on 20m, 13 CW QSOs on 30m, 28 CW QSOs on 40m

DM/BW-089 – Farrenberg – 820m VK/ZL – Europe SOTA S2S Party

Abstract

October 22, 2016: 6:25 – 8:30 UTC

Rig: K3 / 100W, Varta LA60 (60 Ah) AGM- battery, Begali „DXpedition“ paddle
Ant: Vertical End- fed Dipol on 12.5m GRP Pole

39 CW QSOs on 20m – first S2S- QSO with JA and VK 🙂

The 2 kg Challenge

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:

1. Fiberglass pole (10m)
2. KX3 in Go- Box
3. Multiband Dipole with coax

A search for alternatives unfolded:

1. A lightweight 6m fiberglass pole is available but has a slight drawback: The usable height is only about 5 metres.
2. 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.
3. 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.

Next steps:

1. The fiberglass- pole is already available and will replace the 10m Mast in the future.
2. A MTR3B Kit has been purchased. Assembly report is available here.
3. Antenna design hints for a Three Band EFHW Dipole can be found here.