XU7AGA Mentioned in ‘100 Watts’ Magazine

Mr Thossaphol Noratus HS4HNL wrote a lovely article about Ham Radio in Asia for the ‘100 watts’ magazine.  Unfortunately I can’t read it in full myself, but I can see my calls and a few other details in there!

Good job on the article Thossaphol, 73!

Plans for next XU7AGA Activation

Since returning to VK3, I have been really busy with family stuff and finding some decent employment.  However, I’m glad to announce that I’ve got most of it sorted now, and it looks like I will be returning to Cambodia in October or November 2016!

I don’t want to let the cat out of the bag, but it looks like it could be quite an exciting year for DX in Cambodia!

My plans for XU7AGA is to focus mainly on digital modes and ssb phone when I return, and help get as many people ATNOs as possible!

I’ll be sure to keep everyone updated as plans progress,



Planned Activation of IOTA AS-133 (Koh Rong)

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.

The Plan

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.

The Antenna

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.

The Operation

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.

Why Remote Antenna Tuners Are Not Evil

A lot of Hams hate ‘antenna tuners’, and it’s quite understandable given that there are some common and very bad practices concerning tuner usage.


The June 2015 QST Article ‘Don’t Blow Up Your Balun’ explains this better than I ever could – it explains when and how to use a tuner without causing huge losses.  I’ve summarized some of those concepts here, and included some other advantages of using a remote tuner.


Antenna Tuners and ‘Loss’

Back in the days of ladder line, having a tuner in the shack wasn’t such a big problem as the ladder line of the day often had an impedance in the order of 600 ohms, and balanced feed lines are less lossy (have less resistive losses) than coaxial cable when mismatched (being driven into a high SWR).  When you combine their high impedance, (which basically means a lower SWR in a mismatch), with their lower losses under mismatch, having a tuner in the shack was not much of an issue.

However when we switched to coax feeds, we should have moved the tuner.  Coaxial cable has a relatively low impedance of 50 ohms, which means that when there is a mismatch between the antenna and the feed line, the SWR is generally higher.  Coaxial cable also has higher losses (higher resistive losses) under mismatched conditions than ladder line, so when you combine these two things, you can burn up a considerable amount of power just in your coaxial cable.  The solution is to move the tuner, or as we should properly call it, ‘matching network’, to the antenna feed point.

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A little about me, and a little about how technologically amazing ADSL2+ & WiFi are.

About Me

I’m what you’d call a Technician, in the traditional sense – that is to say before the days that being a ‘Nail Technician’ (as in fingernails) was a job.  By that I mean I can understand how something works, and install it, and maintain it for the end user according to the manufacturer’s instructions.  Certainly in some cases I can go beyond that – as I often home brew antennas and what not, but I didn’t have what it takes to be an Engineer professionally.  Read on if you want to find out more:

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No DX Today, The Rain Won’t Go Away…

Here is the view from my balcony in Sihanoukville.  It has been raining solidly for the past few hours, with intermittent electrical activity.  As such, I’m not on the air at the moment… My apologies guys, but it’s wet season here and when every last tall structure you see has a lightening rod attached, well, its just not worth losing my transceiver over!

No DX Today


To be honest, I’m struggling for words.  Obviously, every DXer is familiar with HAMs who decide to ‘break’ into a QSO from time to time, and at least 50% of the time, it is potentially excusable because you cannot be sure they can hear the station you’re communicating with.


By virtue of the way JT65 works, transmissions are an ‘all or nothing’ affair.  Specifically, unless another station can hear your ‘EA7CHS XU7AGA R-16’ transmission, there is no possible way they could decide to transmit back at the same time on the same frequency as the station you’re trying to work!  To be clear,  if you call me on a different frequency, this is ok, although perhaps a waste of time, until I finish my existing QSO: JUST DON’T CALL ME ON THE FREQUENCY WE ARE USING FOR THE QSO!

Today within 30 minutes, the exact scenario above has happened to me multiple times.

This wastes everyone’s time.  I’ll explain why as apparently some people don’t get it:

  • Firstly, I have to re-transmit until I either get a ’73’, or see the other station has given up.  This takes ~6 minutes+
  • Secondly, I have to write the station an email, explain they are in the log, and apologize for the rude breaker
  • Thirdly, I get angry, and waste time writing blog posts like these (and waste my battery).

Let me me clear, if you break into a JT65 QSO I’m having, this is what will happen:

  • You will be ignored for as long as I remember your call sign.
  • If you keep doing it, I may spot your call on the DX Cluster asking why.
  • If you really really annoy me, I’m likely to delete any existing QSOs we’ve had.  I am not joking about this.

The two stations that did the above over and over again today are lucky I’m not naming and shaming them on my blog.  I have no intention of causing trouble within the community, but this kind of behavior really grinds my gears, especially as it normally occurs when I am working a station that is ‘RARE DX’ like the USA or UK.  

Not only do I want ‘rare dx’ in my log, but I am 100% certain that most of the stations I’m working have few if any Cambodian QSOs in their log.

Please be considerate operators, and let me finish a QSO with the station I’m talking to.  This is exactly what you would expect others to do if the QSO was with you.  If you don’t adhere to this simple and basic courtesy, all you will have accomplished is ensuring you never get a QSO with me in your log.  

I’m not the only one who feels this way – please have a look at some of the following links detailing ‘DX Code of Conduct’:

W6SJ’s OP ED Article

ON4WW’s ‘Lets Make DX Enjoyable…’

DX Code of Conduct Website


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