Koh Rong (IOTA AS-133) Activation
This weekend I plan to activate IOTA AS-133. IOTA AS-133 is actually a group of Cambodian Islands, but I will be located on Koh Rong, which is a popular backpacker hot spot where my brother owns a few Hostels.
On Friday the 19th (Cambodian UTC+7 time), I will begin my trip over on the ferry and start setting up the station. I am taking the following equipment:
- Icom IC-7200 Transceiver (100 Watts Barefoot)
- Icom AH-4 Remote Antenna Tuner (Mounted at the base of my Vertical)
- Spiderbeam 12m Telescopic Fiberglass Pole
- Sennheiser HD-25 Mark II Headphones
- Turnigy Accucell-6 Microprocessor Controlled Battery Charger
By virtue of the fact my brother has a fishing boat, I have a few decent 100ah batteries available for use. However, Cambodian power often fluctuates between 180-220 Volts, meaning that most of the local chargers (which are linear devices involving little more than a tapped transformer and some diodes), never fully charge a 12v Lead Acid Battery. My little Turnigy charger, although only rated at 4 amps at 12v, easily charges big Lead Acid batteries to full capacity overnight. As such, it is unlikely I will be on the air on Friday, as I will need to charge the batteries up to full capacity in order to get the most out of my radio.
Using a 12M Long Spiderbeam pole, I plan to setup a ‘multiband’ vertical. The Vertical is ‘multiband’ by virtue of the Icom AH-4 Antenna Tuner / Matching Network that will be placed at the feed point. The antenna will roughly be constructed as follows:
- The first meter or so of the spiderbeam pole will be buried in the sand, preferably with some additional hardware to use as an anchor point.
- Approximately 1 Meter above sand level, the Icom AH-4 tuner will be mounted.
- The driven element will be approximately 8 meters long, but adjustments will be made to ensure it tunes up nicely on 15M. 8 Meters is pretty close to a half wave, but the tuner should handle this fine.
- The counterpoise will consist of 4 sloping elevated wires, two behind me, and two going out into the ocean. Each will be attached to bamboo supports, and the ocean wires will be kept at water height via flotation devices otherwise known as empty plastic bottles. The counterpoise wires will be roughly 1/4 wavelength on 20M.
Computer modelling and the experience of other DXers suggests this antenna should have a gain between 5dBi and 8dBi, with the highest gain on the higher bands. These figures are quoted for low angle radiation, between 5 and 10 degrees take off from the horizon. I suspect the pattern will be skewed towards the salt water, however this is not shown by my modelling software. It is worth noting however that my modelling experience is limited, and I am using a trial version of EZNEC.
Beginning Saturday Cambodia time, WX Permitting, I will begin operation as soon as I wake up (this is an unknown variable). A little bit of time will be spent setting up the equipment, but as I am planning to use a vertical antenna located right next to / in the salt water, I expect this will take less than 30 minutes.
Depending on band conditions, I will be using a mixture of PSK-31 and SSB Phone. My preference is SSB Phone, so hopefully propagation will be nice.
I plan to operate on the 15M, 17M & 20M Bands, with preference going to the 15M band as it seems to shine in this part of the world.“
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