VK2TRF in action

"Amateur Radio" Articles

Here are a number of recent articles for Amateur Radio magazine written by club members. The picture shows Jack VK2TRF on top of Mt Coree as part of the Grand Slam ATV attempts.

Raffy VK2RF

Simon VK2UA Richard VK2XRC Jack VK2TRF


VHF/UHF Squid Pole Antenna Mast

Illustrations for this article can be seen in our photo gallery.

This is a suggestion for a simple, quick and easy VHF/UHF antenna mast for portable operation. All that is needed is a suitable antenna such as a Diamond or similar which has a short aluminium tube support for the base, the antenna feed line, and a seven metre or similar squid pole.

To erect the mast, pull the rubber bung out of the top, unscrew the cap from the base of the squid pole and withdraw the two top sections so that the top of the remaining section is large enough to pass the PL259 connector. You may need to remove the rubber knob on the top of the top section to be able to withdraw it satisfactorily. I suggest that you use at least a ten metre long feed line because you will need five metres to go up the mast. It is easier to slide the end of the co-ax feed line up the squid pole before you start erection. Run the cable out straight so it does not get kinked. Slide the aluminium tube mount over the feed line and the top of the squid pole. With the feed line fed up the squid pole, connect it to the base of the antenna and then slide the aluminium tube antenna support base onto the bottom of the antenna and do up the retaining screw or bolt. Slide the antenna onto the top of the squid pole and then erect the squid pole. Tie off the squid pole to something firm. Connect the feed line to the radio and away you go.

Try not to lose the rubber tip, the two top sections from the squid pole, the rubber plug for the top or the plastic and rubber base cap so that you can put it all back together when you are finished. You can either guy the mast with some venetian blind cord or bricklayers’ twine or fix it to your tent post or a fence post with an electrical tie or two.

The system is useful for a quick portable set-up where you plan to move on. If it is windy or you plan to be there for a while, ensure that the sections are firmly engaged.

If you are sensitive about scratching your squid pole, you can wrap some insulation tape around the squid pole at the bottom of the aluminium support tube to provide some resistance to chafing.

Have fun operating portable!

Richard Cortis
VK2XRC


Charging around in the Campervan

Last year my wife bought herself a little Toyota Hiace campervan which we have put to good use over the last year. However, we have suffered ongoing difficulties with the house battery. The campervan has two batteries, a normal starting battery as fitted by the manufacturer and another battery to run the refrigerator, cabin lights, water pump, amateur radio and those sorts of thing. The two batteries were connected together by a solenoid switch which came on when the ignition went on and disconnected when the ignition went off. There was a current limiting device (circuit breaker) between the house battery and the starting battery to reduce engine starting loads on the deep cycle house battery.

Our problem was that the house battery appeared to have a significantly reduced discharge capacity than expected. The battery also had a much shorter service life.

We drove the campervan to Perth. Many thanks to those kind amateurs who run the various travellers nets. In Perth I accidentally left the headlights on for half an hour and the engine wouldn�t start so I replaced the starting battery before heading back to Sydney. However, half way across the Nullarbor Plain, the deep cycle house battery gave up the ghost and, at great expense, a new deep cycle house battery was installed in Port Augusta. After a few days on the way back to Sydney, the performance of the house battery declined significantly. In Sydney, I was able to take a much closer look and discovered that both the starting battery supplied in Perth and the house battery installed in Port Augusta were calcium batteries which are a much newer technology than the old flooded lead acid type.

I took advice from various parties and decided to deal with the simple and low cost matters first. I was told that there were occasionally problems with fusible links and high resistance in cables from the alternator to the battery so I replaced that cable. I also installed a new cable from the starting battery to the house battery. Because of the possibility of high resistance in the original ancient solenoid switch, I replaced that with a new solenoid switch capable of supplying a starting current if need be. Just in case. I upgraded the ground connection from both batteries. However, none of these had any measurable effect. I even paid a fortune to an auto-electrician who told me that I did not have a charging problem.

Then I started to look more closely at the battery characteristics. A traditional flooded lead acid battery can be reasonably charged at about 13.8 volts. The batteries electrolyse less water and perform satisfactorily if they are run at about 13.5 volts. However, the newer technology calcium battery needed to be charged at at least 14.2 volts I was told. If it was run at between 13.5 volts and 13.8 volts it would slowly discharge. If they do not get the higher voltage during charging, they develop only about half of the rated Amp Hour capacity. I was getting somewhere.

I then took to driving around with a multimeter connected to the battery so that I could observe charging voltages under normal operational circumstances. This turned out to be quite interesting. I observed that with all accessories, fan, air-conditioning etc turned off, the battery would come up to 13.8 volts but that it required effort and perseverance. However, driving around with the air-conditioner on gave me 13.5 or 13.6 volts depending on whether the clutch was in or out. When I turned on the headlights, the voltage went down to about 13.3 volts. At this stage, it became blatantly obvious that the problems with the house battery were related to insufficient charge voltage.

I made some enquiry with auto-electricians regarding upgrading the regulator or, heaven forbid, installing a new alternator. They were not at all keen to play with regulators. The suggestion was to replace the alternator and see what happened. However, at an expected cost �probably between $700 and $800� I was disinclined to proceed down that road especially as there was no guaranteed end result.

charge diagram After this episode, I decided that I had to do something decisive for myself and that it was going to be a low cost approach. There did not appear to be anything physically wrong with the alternator except that the regulator voltage was set too low. I was most disinclined to remove the alternator from the vehicle because, being a diesel, the alternator has a vacuum pump which runs the power brakes and I did not want to risk disturbing that system. So there had to be another approach. I recalled from other projects that I could use diodes to drop voltage. Perhaps, I thought, I could trick the regulator in the campervan into operating at a higher voltage. So I planned to insert a couple of diodes in the sensing wire from the battery to the alternator. The intent was to let the regulator see a lower voltage which would make it charge at a higher voltage to compensate. Ordinary silicon diodes have a voltage drop between about 0.5 volts and 0.7 volts. I went to my junk box and found a rectifier bridge which I guessed was good for about 15 amps. As the expected exciter current for the alternator was expected to be about 5 amps, I reckoned that the rectifier bridge would be satisfactory. The voltage drop across each of the diodes was about 0.55 volts. At full exciter current without the regulator cutting in and out, I expect to have to dissipate about ten to twelve watts. Then I had another idea. Since we regularly run the house battery a fair way down, we need to bring it up fairly quickly if we are camping. My wife does not like the engine running in nice quiet camping places. So the idea was to wire the rectifier bridge so that there were two diodes in series in the sensing line. I then put a switch across one of the diodes so that it could be shorted out, leaving just one diode in the sensing line. This gave me the ability to run the alternator at 13.8 to 14 volts under normal long distance driving conditions or, where necessary, to boost the voltage to 14.2 or a bit above under heavy charging conditions. The switch allows me to switch back to normal charging voltage after the battery has been charged.

There are a couple of points to consider when planning this sort of modification. Firstly, the type of alternator may determine whether you install the diodes in the sensing line or in the ground cable between the regulator and ground. Also, operation of the charge indicator light on the dash may need some current to flow in the opposite direction. The system is inductive so there may be transient currents in the opposite direction. For these reasons it is desirable to install a second set of diodes in the opposite direction to avoid such problems. The diode bridge achieves this intent. Wire it up by shorting between the positive and negative terminals with a lead off to the switch. Connect another lead from one or other of the AC input terminals to the switch. Connect the diode system into the sensing line at the AC input terminals. You will see that there is the same voltage drop in each direction, switchable for about one volt or half a volt.

So I decided to have a go with the diodes. With a little bit of assistance from Tony, VK2FREL, who is a mechanic, I removed the driver seat, removed the floor beneath the driver seat and exposed the alternator. Tony arrived, identified the sensing line and the diode was installed and running in about twenty minutes. Charging voltage came up and we could switch to normal charge or high charge. We have been successful.

Most of the components come out of stock so I cannot say what it would have cost but my guess is that it would be under $20. Had I used this approach in the beginning, I would have saved a fair bit of time, effort and expense, but I would not have had the learning experience. I guess all this is just part of life.

And as a final note, take care when changing from old to new battery technology in old vehicles as the new technology batteries may not perform satisfactorily if the charge voltage is too low. Checking charge voltage may be misleading if your battery has ceased to be reliable as it may not come up to voltage

Richard Cortis
VK2XRC

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Market Umbrella Antenna Mast

Illustrations and drawings for this article can be seen in our photo gallery.

Some time ago, the local coffee shop threw out some market umbrellas. Being a little more fanatical than your average dumpster diver, I picked one up and brought it home because it had some good timber which may have been useful for something one day. The sun had done its job on the umbrella canopy but the timber structure was in good order. Recently, I had a rush of blood to the head and decided to re-configure the geometry of the umbrella to turn it into a portable amateur radio mast. This is the story of how I did it.

The market umbrella was a typical four sided timber framed market umbrella with a fixed hub at the top and a sliding hub to support the braces. There was a brass pin to hold the sliding hub in position when the umbrella was erected.

The first thing I did was to remove the canopy and throw it away because it was just too rotten even for a painting drip sheet. I then removed the arms from the fixed hub at the top of the pole and then I removed the braces from the sliding hub. This was fairly simple and required only a pair of pliers to untwist the wire fixing the arms and the braces to the hubs. I then took two wire coat hangers and reversed the arms and the braces so that the braces were attached to the fixed hub on the end of the pole and the arms were fixed to the sliding hub on the pole. Fixing the arms and the braces back onto the hubs was a little bit of a hassle, mostly because my grandchildren were trying to help. In the normal course of events, it is a fairly simple activity where the coat hanger wire is formed roughly into the circular shape of the hub and then threaded through the holes in the arms The arms are then set into the recesses in the hub and the pliers are used to twist the wire and tighten it. I did the same thing to reinstall the braces on the fixed hub.

I then set the modified device on the ground and attempted to erect it. I found that the original hinge position needed to be changed for two reasons. Firstly, the distance from the fixed hub to the hinge point on the arm was about the same as the length of the strut so that, when the sliding hub was moved as far as it could, the braces ended up almost parallel to the arms and the arms lay flat on the ground, leaving the device somewhat unstable. The second reason that I moved the hinge point was to make the device fold more compactly than the umbrella. I moved the hinge point (the point where the brace attaches to the arm) about 200 millimetres towards the tip so that, when folded, the arms sit neatly against the pole, beneath the fixed hub. This also has the effect of stabilizing the geometry so that the sliding hub can be moved towards the fixed hub without the device becoming unstable.

The only carpentry work was to drill the four holes in the arms. The only tools I used were the pliers, drill and 5 millimetre bit, screw driver and a hammer to peen over the ends of the threads on the new hinge pin bolts.

Market umbrellas with eight arms can be treated similarly but you may consider only reinstalling four of the arms to save weight and complexity. I do not recall having seen a six-sided market umbrella.

So what did all of this cost? Well, the coat hangers cost nothing because I picked a large bundle off a previous Council clean-up and the four machine screws, four nuts and eight washers came out of stock.

And how long did it take me? Even with the grandchildren helping it took a bit over half an hour.

The finished product is a bit like a large version of a camera tripod but a lot larger and a lot more stable. It will support VHF and UHF beam antennae and verticals and will even support one end of a long wire or the centre of a dipole. There are many options.

I thought it was worth the effort and one of the members of the Waverley Radio Club liked it so much that I decided to give it to him as he has possibly more use for it than I do.

Richard Cortis
VK2XRC

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Page maintained by Simon Buxton. Created: 20/1/00 Updated: 9/11/2011