Home brewing a Vertical for DXing

Recently, I’ve been bitten by the 80M DXing bug.  Its not so much that 80M has taken hold, as it is that I have managed 140+ confirmed on both 40M & 20M now so all the ‘easy pickings’ are gone.

My main antenna is a 102ft ladder line fed dipole aka G5RV up ~45 feet at the Apex.  Whilst this antenna takes QRO in its stride, and puts out one heck of a signal, it also features a whole lot of ‘high angle’ radiation on 80M & 40M.

Whilst I’ve managed 30 countries on 80M running some power (which was needed), I always found received signals to have poor SNR.  As such, I decided to once again revisit the Vertical – primarily as an RX Antenna for now – to see if it could help.

Here is the pattern difference, in theory.  Note the huge amount of high angle radiation the G5RV (broadside) picks up compared to the Vertical.  Although the low angle figures look close, remember the G5RV has a ‘peanut’ shape even at 45ft, so when the G5RV is facing ‘narrow side’ the Vertical has over an 8dB advantage below 15 degrees.

Screenshot 2017-05-21 19.46.50

Continue reading for more pictures and information about the project 🙂

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VK3BL Rack… Icom IC-7300 Still Wins!

So, despite my best efforts to date with the DBX equipment pictured below, the stock IC-7300 mic pre-amp and compressor still gets slightly better on air audio reports!

A true testament to how good the Icom IC-7300 sounds out of the box, especially with a Heil Microphone!

I’ve sunk over 30 hours into this setup so far, so my recommendation is to people unless you like fiddling, keep it simple and stick to plugging the microphone into the front!

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Just passed my advanced exam!

Today is an exciting day day for me!  After getting off my bottom and finally sitting the ‘full call’ advanced exam, I passed with 84%.  For those out there who are looking to sit this exam, the Amateur Radio Victoria practice exams are really good.  They can be found here:  ARV Advanced Practice Exams

Although I didn’t really formally study as such (I sat the practice exams and did about 2 hours of revision / cramming), I have spent the last year or so reading pretty much continuously about radio as I am pretty much addicted!

I got a few silly questions wrong, mainly resistor color codes!  I can’t believe I stuffed that up, but to be honest even the assessor thought it was unexpected that it would be on the advanced exam.  The fact is, I’m a little intellectually lazy, and just refer to the color chart or my fluke DMM when working with resistors!

There were a few ‘give away’ questions, like what length a specific band dipole would be, so it is good to make sure you know that stuff off by heart before you sit the exam.  The truth is though, any keen amateur who plays with antennas a bit should find those kinds of questions to be bonus marks!

The ‘hard’ questions on my exam tended to be about linear amplifiers.  When they are needed, what the different classes are etc.  As I am really interested in linears, I found this a breeze!

So there we go, I’ve applied for my full call, and hopefully will have the call sign VK3AGA shortly.  It will be nice having a call that matches my Cambodian one, XU7AGA!

73,

Jarrad

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!

What does it take to work 100 Countries? Not Much!

Even though I have a really modest station at the moment, over the last year I have been able to work over 100 DXCC Entities without too much difficulty.  Today I though I’d share the details of my basic setup; hopefully to inspire other would be Hams or current Hams who don’t use HF to give it a go.  The following gear is all you need to get your Basic Mixed DXCC (at least from Australia), and the total cost should be less than ~$1750 USD:

  • Icom IC-7200 Transceiver
  • Icom AH-4 Remote Antenna Tuner (a remote tuner significantly minimises loss in feed lines)
  • ~5 Metres of 1″ Aluminium Tube (for element)
  • ~100 Metres of 1.5mm^2 Wire (for radials)
  • 1 Star Picket for the ground
  • Miscellaneous insulating material and a few hose clamps.
  • 32 Ferrite Beads (for tuner control cable & feed line)
  • Coaxial Cable (I used Belden LL-195)

The Icom IC-7200 is a great value budget transceiver; it does everything a new Ham could want, and more.  Some standout features are: easy to use IF DSP with dedicated knobs, built in USB for CAT & Audio (digital modes are easy to use), control for Icom AH-4 Tuner, rugged and low cost.

The AH-4 is a wonderful tuner, and the fact it is mounted at the antenna means that loss due to high vSWR (which mostly takes place in the feed line) is significantly reduced.  Not only is it one of the smallest on the market, it also matches a very wide range, and works perfectly with a vertical element of a random wire.  I have found performance to be excellent when used with a vertical element, as the take off angle is a lot better for DX work than a low height random wire.  The only catch is, unless you put ferrite beads on your feed line and control cable, you may run into issues with RFI in the shack, although this is not an issue with the tuner itself.

All in all, the aforementioned basic setup has brought me a lot of joy; I also used a similar setup in Cambodia and managed 70 DXCC entities in 6 weeks.  If the aluminium tube is substituted for a fibreglass telescopic pole with a wire taped to it, the setup makes an excellent portable station, however these poles are best not used in a permanent installation as they will not last as long as an equivalent aluminium tube and are more expensive.

Here are a few photos of the gear (the radio photo I borrowed from Google Images, but mine is the same):

photo 320970

The moral of the story is you don’t need to be rich to enjoy DXing on HF!

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…

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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