Solving Stereo / Home Theater Radio Frequency Interference caused by Ham Radio

Having suffered DX withdrawal, I decided it was time to put up a new antenna.  The antenna in question was a Icom AH-4 Tuned Dipole of about 36M length in total, about 9M high at the apex.  Whilst I realize it is far from optimal in many ways, I was interested to see how it would perform on the higher bands, and thought it might significantly improve my local contacts on 40M & 80M.

It seems to have delivered on 80M, my local Winlink Winmor speeds on 80M have gone from 100 Bytes / Minute to a huge 1100 Bytes / minute, and I’m once again hearing the local farmer’s nets!

However, there is much testing to do, and the story today is about the problem the new antenna caused!  I like to play on JT65 at night, when there isn’t much going on, and I’ve setup my radio so I can do so remotely via my laptop.  Whilst relaxing in bed playing JT65 on 20M, I decided it would be a good idea to listen to some music, but my new antenna thought otherwise!

My home stereo system is pretty basic but nice.  It consists of an Audio Engine DAC (usb sound card), and a Miniwatt N3 3.5 Watt Tetrode Amp.  A good friend of mine, Peter VK3OJ, had recently given me some old (but working) 12AU7 tubes, and I was keen to see how they sound compared to some of the newer models.  However, the moment I transmitted on 20M, the left speaker would buzz, and the computer dropped the soundcard!

At first, I decided to tackle the buzzing speaker.  I added some chinese (ebay sourced) snap on ferrite cores one by one and transmitted, until the buzz died down.  It took 12 snap on cores to achieve a decent result, however this didn’t stop the computer from dropping the soundcard.

I then put 4 snap on cores on the USB lead, but that didn’t help.  I added another 4, and hey presto! I could now listen to music and DX!

The moral of the story is that the age old solution to RFI of snap on cores works, even with cheap ebay sourced chinese cores!

If you’re like me and enjoy listening to music while using digital modes, or have a neighbour who has issues with RFI on his sound system, you couldn’t do better than buying a bunch of snap on cores on ebay.  Many Chinese sellers will sell them in bulk (shop about, put ’10’ in your search etc), and I was certainly glad to have these ones in the shack!

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Grumble of the week: Why no one runs permanent PACKET/IRLP/ECHOLINK/WIRES Nodes!

After doing a bit of reading, there are two core issues:

  • The band plans don’t allow for much spacing between the aforementioned nodes & FM Simplex / Repeaters.
  • ‘Commodity’ Amateur 2 & 70 Radios have very little front end attenuation.

I haven’t tested it (and I won’t) but I can’t imagine running 50 Watts on an Internet Linked WIRES Gateway on 145.325 at the same time as trying to operate FM Simplex or even VK3REC 147.175 (1.85MHz Spacing Maximum) is a great idea, given that the Antennas at best would be within 20M of each other and with an average gain of 6dB each (aka you might as well transmit 5 Watts directly into the other radio).

I did actually calculate that*; on 2M the path loss of 2 antennas with 6dBi gain 20 Metres apart is 9.7dB.  That means if you TX 50 Watts, the other radio will receive 5 Watts of power.  I don’t design RF front ends for a living, but S9 VHF is defined as 5 uV (0.000005 Volts).  5 Watts @ 50 Ohms = 15.8 Volts (P=V^2/R)!!!  Simply put, without using cavities, you are looking at a ~S9+130 situation at best, but more realistically a blown front end stage.

*My calculations assume both radios are tuned to the same frequency.  That said, I’ve done a bit of reading regarding repeater building and apparently modern FM radios offer less than 1dB of attenuation across a 3 MHz spread (prior to the front end filtering).  The ARRL test reports disagree with this in a sense, suggesting 55dB of rejection with 20kHz channel spacing, but I’d imagine their test did not involve *significant* front end overloading – just a simple adjacent frequency test in the microvolt level! 

From what I have read, most 2M repeater builders find they need to use between 80 and 100dB of Duplexer / Cavity Attenuation to avoid de-sensing the receiver.  This makes sense, as ~80dB of cavity + 55dB of front end rejection would take care of S9+130.

Has anyone got any ideas of how I could operate a permanent Wires-X (IRLP/EchoLink Equivalent) node at my QTH?  The best I’ve come up with so far is setting up the Wires-X Gateway on 6M using a Yaesu FT-8900R, which at least is not harmonically related to 2M & 70CM.   

The only downside to that is whilst I have a 6M Handheld and a 6M Radio for the car (my Yaesu FT-857D), running the Wires-X Link on 6M limits the potential audience, as a lot of people just have 2M & 70CM rigs, especially mobile where it would be interesting.  No current manufacturer even makes a FM Mobile or HT that includes 6M!  Simply put, other than myself, I can’t imagine a 6M Analogue FM Wires-X Node would get much use!

All of the above leads me to one conclusion.  The reason no one runs permanent Packet/IRLP/EchoLink/Wires Nodes at their QTHs these days is that it requires one of the following:

  1. Investing in a full repeater grade duplexer / cavity solution, or:
  2. Giving up either 2M or 70CM at their QTH.

Given that FM Phone on 2M & 70CM is by far one of the most popular modes, and most Amateurs would lack the resources to build a repeater grade solution, it is little wonder no one bothers with permanent ‘esoteric’ modes such as Packet/IRLP/EchoLink/Wires.

 

Feel free to correct me if I’m wrong…

My Current Home (Australian) Station

Hi Everyone,

Below is a few pictures of my current station in Australia.

It basically consists of the following:

  • Icom IC-7200 HF/6M Transceiver
  • Yaesu FT-101E HF ‘Hybrid’ Transceiver
  • Yaesu FT-857D HF/VHF/UHF Transceiver
  • Icom AH-4 Remote Antenna Tuner
  • Daiwa CN-801 ‘HP Type’ 1.8 – 200 MHz Cross Needle VSWR Meter
  • Daiwa CN-801 ‘V Type’ 140 – 525 MHz Cross Needle VSWR Meter
  • DOSS SPS-8400 40 Amp 0-15v Power Supply
  • Mac Pro Desktop Computer

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Revised QSL Card Design & QSO Rundown

As previously mentioned, the original QSL Card Design wasn’t compliant for the IOTA awards, so here is the new one.

Basically, if you get a QSL card with ‘Koh Rong AS-133’ ticked, it counts for IOTA.  If ‘Sihanoukville’ is ticked, it doesn’t.  All QSOs made with me between the 19/06/2015 & 21/06/2015 UTC were made from Koh Rong Island, IOTA AS-133.

In total, there were 92 IOTA QSOs. Although I would have liked more, it is wet season here and the weather was absolutely terrible.  Japanese stations collected the majority of QSOs, although even these pile-ups were frequently ended by the WX.

Honorable Mentions go out to: W6CCP, W6ZR, KH6HM, W4DJL, S52LD, UA0FDQ, SP5FCZ, YO8BGE, and Wim (XU7TZG), who managed a QSO on every band (except 160m which neither of us could tune) 😉

If you have any questions regarding whether your QSL counts for IOTA, please email me via my QRZ listed email address.

XU7AGA Back Small XU7AGA Front Small

Unconditional Proof that I’m in Cambodia – A Beer with Wim (XU7TZG)

Anyone who has ever though about operating in Cambodia knows of Wim (XU7TZG).  Wim is the Elmer of Cambodia – he knows the licencing procedure, hes been here many years, and he even knows which local beer is the premium product.

I know I’ve posted my licence, and I could easily post a picture of my passport with Visas, but documents are documents and I don’t want to be another Don Miller or Romeo.  So here goes, here it is, unconditional proof to those who believe that I’m here in Cambodia:Jarrad and Wim

A Quick Tour of my First QTH Station!

This is my station at the moment, not all the equipment is mine (the IC-7000 & FT-90R are on loan from VK3HBN). The Alinco DX-SR8T is my favourite; although its a basic rig, i’ve had fun reverse engineering it in order to tap the first IF and connect a RTL-SDR dongle as a panadapter, and it will control my Antenna Coupler.

More Pictures Below

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