Archive for the ‘Home Brew’ Category

Holiday Operations- I Get to Work HF Again

December 22, 2016 2 comments

The problem with living in Sydney is not just the issue of trying to build or purchase a HF antenna that can be fitted onto the balcony of a one bedroom apartment, but also the problem of an S9 noise floor. So it was that when I was asked to do some dog sitting at my RF quiet North Queensland residence, I packed a HF radio.


Of course, a radio is not much good without an antenna, but in my usual style I decided the best approach was to build one from scratch. I wanted to work only 80m CW and 40m phone and I could have chosen a dipole but the yard is a bit small. I had in the past constructed a 40m/80m trapped sloper referred to as a Lake Eyre Special and I figured this would be the ideal antenna. There are several tall Royal palm trees that would provide the necessary elevation.

I started by purchasing some speaker wire and splitting it into single wires then would 120 turns on to a 40mm pvc form. 10.04 m of wire formed the 40m section which I then tuned using my antenna tuner which I always pack in my holiday baggage :-). I then fitted the coil and double checked the tuning. A slight change to the coil of a few more turns had me back in tune. I then added the top section 1.6m and checked the tuning on 80m. Despite my error of tuning to 3.1MHz instead of 3.6MHz, I finally got things correct. The antenna was hoisted into the tree via the usual sling shot and fishing line method. I always carry my slingshot on holiday for this very purpose.

Now to work some 80m CW in the mornings

73 de VK2KMI es VK4KIM

Categories: HF, Holiday, Home Brew

The Monster will Live Again

September 6, 2016 2 comments

You may recall The Monster is Deaf

But look what I ordered!

KP1-4 10-500pF 10kV Vacuum Variable Capacitor


I have new plans for the monster, to get it away from the building and to better tune it

It may have to wait until I move to a new home, but the plans are underway and this capacitor is an integral part of those plans


Categories: HF, Home Brew Tags: , ,

Of Slinky Springs, Apartment HF and ALARA

August 29, 2016 2 comments

The weekend just gone, I wanted to participate in the ALARA (Australian Ladies Amateur Radio Association) contest. I knew that with my poor antenna I was not going to make many contacts, so I set about building the optimum multi band apartment antenna.


I gathered together slinky toys, some chord and a few bits and pieces. A local ham sold me a short length of 300 ohm ladder line with which to feed the antenna and using a few bits an pieces, I assembled a 1:1 current balun to allow my unbalanced tuner (a Z11 Pro) to connect to the 300 ohm line. with this antenna I intended to overcome all of my antennas woes of the last few weeks.

With the antenna analyser I got the dipole resonant on 80 m and the tuner then allowed me to get a match on all bands including the WARC bands.

Unfortunately  the construction of my balcony with its aluminium framing makes the antenna deaf. A full 4 S points down on the tiny mobile whip. I am confident the antenna will perform well once I get it away from the building structure. I move out of this apartment in November and will be looking for a place more suited to antennas.

I will post more about the construction of the slinky dipole in a later post.

Categories: Daily News, HF, Home Brew Tags: , ,

The Monster is Deaf

August 22, 2016 3 comments

80m Apartment HF- The Monster in My Bedroom

Taming the Monster

Screen Shot 2016-08-22 at 18.57.53

One thing that can be said is that ham radio experimentation is never dull, this is doubly true if the experimenter lives in an apartment in a high rise building. After creating the monster mag-loop antenna in my bedroom and tuning it for resonance and best SWR, it turns out that it hears RF (hash) really well but can’t hear a signal that my little mobile whip mounted on the balcony rail can hear well. Seems that my suspicions that the building is a faraday cage may well be true or at least that the antenna capacitively couples to the building making it deaf to external signals. Unfortunately the loop is far too big to put on the balcony rails so time for plan B.


Taming the Monster

August 21, 2016 1 comment

Recently I fabricated a large mag loop 80m Apartment HF- The Monster in My Bedroom– now it is time to tune it, to tame the monster so to speak. I decided to feed the loop using a twisted gamma match because this seemed the easiest to make with the materials I have. I live in an apartment and all of my workshop tools etc are in storage two thousand kilometres away.


The twisted gamma match is proving more difficult than I thought but I am getting close to figuring it out. I am using a length of RG213 coaxial cable as the capacitor, with two printed circuit boards as the trimmer capacitor. The antenna in it’s present configuration is resonant at 3.55 MHz with the trimmer set to highest capacitance so it looks like I have to add more capacitance- a longer piece of coaxial cable. The cardboard between the two plates in the image above slightly increased capacitance.



80m Apartment HF- The Monster in My Bedroom

August 20, 2016 4 comments

I have been toiling away on a mag loop antenna for the 80m band. I needed it to be cheap, I also wanted to be able to use it on other bands later, with some modifications.

Since my balcony is not really big enough for a larger mag loop, I decided to make a loop that took up the entire wall of my bedroom which is my radio shack. The problem with this idea is that I suspect the building is one huge faraday cage. We will see when I am finished. If it turns out that it is a faraday cage, I will go to plan B which if it happens, you will see blogged here.

Screen Shot 2016-08-21 at 06.33.52

To keep costs down I made the capacitor out of RG213 coaxial cable which has capacitance of about 1pF/cm thus my design required aprox 195 cm of cable. Tuning will be via a homemade trimmer capacitor consisting of two printed circuit board blanks attached to the end of the coaxial cable. By making this cable removable, I will be able to interchange various lengths to change bands.


OpenSprinklerPi Control Box Completed


Well finally after a few challenges, including letting the magic smoke out of a few components, the OpenSprinklerPi control box is complete and working. Though I still have to complete the actual inground irrigation piping.


The control box contains

240 V AC to 24 V AC transformer

OpenSprinklerPi unit v1.4 with raspberryPi computer

Extension board unit for more sprinklers

Home made full-wave bridge rectifier to convert ac signal (pump on) to DC

Ripple filter

Relay to switch the pump on and off


The OpensprinklerPi allows automation of the sprinklers and operation via any device that can access the server including my iPad and iPhone. A weather sensor adjusts the sprinkler program to account for rainfall.





Categories: Home Brew