GGREC 70cm Repeater (September 2006)
CTCSS FOR IRLP IS NOW 123Hz
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A Folded Dipole (September 2006)
( borrowed from www.elmerhamlet.com)

A variation of the dipole is an antenna called a folded dipole. It radiates like a dipole but sort of looks like a squashed quad.

Having a folded dipole does not mean that you have an antenna that is folded in half and so you obtain an antenna that now takes up half the space of a regular dipole. No, the antenna is still approximately the same length as a regular dipole. It is however, an antenna that has a wire folded back over itself, hence its name.
The starting formula for the folded dipole calculation is the same as a dipole, 468 / Frequency (in MHz). Let's try an example: Design a folded dipole for the 40 meter band. The frequency that is chosen might be 7.15 MHz. Plugging this in to the formula (468 / 7.15) gives a folded dipole with a length of 65.45 feet. When I modeled a dipole on the computer at 30 feet, I came up with a length of 65.47 feet. When I added a second wire to make the folded dipole shown above, I designed the antenna with 1 inch spacing between the two wires. Note that this adds 1 more inch to each of the two antenna wires over that of a single wire dipole. This plus the fact that we are actually turning up the ends of the antenna, means that the horizontal length actually need to be a little shorter to be once again at resonance. The total length came to 64.38 feet, 1.09 feet shorter than the straight dipole. If you use a greater spacing, say 1 foot between the wires the length is 63.1 feet, 2.37 feet shorter. So be sure to shorten the antenna a bit or you'll find yourself operating lower down the band than you expected.

The feed point impedance is also modified by the second wire. Let's say the original dipole was 72 ohms. The step-up for a two wire folded dipole is 4 times which means 4 * 72 = ~288 ohms. (The computer shows 281 ohms on my example, but remember, we reduced the length slightly also.) This step up continues if you add more and more wires. A three wire antenna would provide a step-up of 9, and a four wire antenna provides a step-up of 16.

We can see why this step-up occurs by looking at the power formula P=(I*I) * R, this can be rewritten as R = P / (I*I). If the power to a regular dipole antenna was 100 watts and the current was 1.2 amps, we'd solve for R as R = 100 / (1.2*1.2), which is the same as R = 100 / 1.44, which is 69.44 ohms. In the folded dipole the wires are in parallel, the current must be divided between the two wires. The current in each is half and the total power has not changed, so now the formula is R = 100 / (.6*.6), which is the same as R = 100 / .36, which of course is 277.77 ohms, 4 times the normal dipole antenna.

So now you ask, why would anyone want an antenna with a feed point impedance of 277 ohms, my coax cable is 50 ohms!? Well let's say you wanted to feed the antenna, not with 50 ohm cable but with 300 ohm twin lead? Ah ha, now we have a decent match and a feed line that can also handle a higher SWR with low loss. You'd probably use a tuner (ATU) in the shack to match the 50 ohm radio to the 300 ohm feed line.
You could also use the antenna on other bands with the tuner and have an efficient antenna system.

What are the drawbacks to the antenna? Well for one, the currents on each wire will begin to cancel each other out on even multiples of the cut frequency, so a 40 meter folded dipole should not be used on 14 MHz. On other bands even though the signal may cancel broad side to the antenna, you'll find that there is actually gain! This occurs about 45 degrees off broad side to the antenna. And this might make for interesting contacts.
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THE WICKED WINCH OF THE EAST (August 2006)
By Ian Jackson 3BUF
Recently several members of the GGREC purchased new brake-winches to replace the basic winch assemblies on their radio towers. Most of these were for the two-stage, tiltover ‘Nally’ radio towers which use two winches. Why do this’ you may ask? Or more to the point, if you don’t ask, then there’s no reason to read this article.

The Original winch assemblies on the Nally towers were a very basic 1:1 ratio pawl & ratchet assembly. Pretty much like what you would see on the village well in an African Foreign Correspondent documentary. When you wind it up you get a clack-clack of the pawl riding over the ratchet. If you let go of the handle, the pawl locks into the ratchet and the winch cable remains in a safe state. All sweet if you are winching ‘up’ the mast (or bucket). The fun starts when the tower is being lowered, (it’s ok to stop thinking about buckets now) because you must use one hand to hold the safety pawl back, while unwinding the winch handle with only one hand. This can be very heavy indeed. If your one hand should slip from the handle during this process, you have a runaway tower. The top stage drops like a pile driver, the handle spins out of control, breaking whatever bones it can. When the tower bottoms out, your multi-hundred dollar antenna rotator crumples like a Styrofoam burger container under the front tyre of a Hummer (with the burger still inside!). Approximately 2.7 seconds later the sky rains aluminium from what was your antenna system. There are words that would be spoken following this chain of events which gentle ears should not hear and my spellchecker cannot deal with. Fortunately this has not happened to me, but it is a spectre that does haunt us all.

There is a solution. Enter the ‘Brake Winch! (insert mental image here of a hand whisking away a violet silken handkerchief from something on a pedestal that could be a brake winch) The popular brake winch has two advantages. Firstly, it usually has a gear reduction which makes it easier to wind up and down. You will no longer need that well oiled and bare-chested rower from a Cleopatran river barge to crank the tower for you. (unless of course you enjoy having him around) Secondly it has an inertial brake. You can un-wind the winch safely and let go at any time without dire repercussions.

Now we get to the good bit. First buy your winches. You will need a winch in the 260 to 300kg range like the Jarrett F18230 brake winch, or the Rig-mate BRWH270 from Nobles rigging supplies in Dandenong. They are around $80-$90 each. Many of the GGREC members purchased the 500kg BRWHB500 version which is a larger, heavier winch. After some experiments with both winches, I preferred the smaller BRWH270 because of the shorter winch handle which did not clash with the tower and better cable departure angle from the spool.



The first stage was to secure the tower, un-wind all the cable from the old drum and grind off the old winch assembly. The second stage was to drill the 10mm holes in the steel adapter plates. These plates were standard 110 x 10mm flat stock cut to size by a local steel merchant. It was much easier to pre-drill the plates in the drill press than to do it on the pole. The plates were then welded into position, tidied up with a grinder and sprayed with undercoat. The plate was 400mm long for the vertical lift winch and 150mm long for the tiltover winch. The vertical welds can be a bit of fun to get right, but remember that the worst welding job will still be better than the best duct-tape and garden twine job you can do.

To prevent unwanted angst and loss of enjoyment to life, I highly recommend not wearing your favourite polyester house slippers during the grinding and welding phases. Of course you will then lose a great talking point around the coffee table when your guests ask why your white socks can be seen in a kind of reverse-Dalmatian style through your dark blue slippers. (Before you know it department stores will want to sell pre-welded slippers alongside their pre-washed, pre-holed denim products. Be a trendsetter!)

When attaching the winches to the plates, use 10mm x 30mm stainless bolts, with matching washers and nuts. The stainless bolts have a higher tensile strength than equivalent mild steel ones, and of course they will not rust. The difference in cost is minimal. In fact, check the integrity of your winch cable during this upgrade. Remember the mantra: If it’s brown, tear it down. If it’s clear, have no fear. On my tower I found some corrosion on the tiltover cable where it passed through the lower pulley. I replaced it with some 6mm dia stainless cable and stainless wire rope clamps.

To keep the winches looking pretty, you may want to cover them with a bag or something. On the vertical lift winch, tie a bit of rope or scrap cable around the wire above the cover, so that when the water runs down the vertical cable, it will drip off the scrap wire before entering the cover and wetting the cable on the reel all the time.

I usually use a counterweight on the rear of the tower to make life a bit easier. It is a slab of steel with a removable mounting hook. With the weight in place a three year old kid could work the winch. Mind you, that same three year old may find it awkward to drag the 60 kilo slab of steel into position, and he would also need a decent box to stand on to reach the handle, but all of these difficulties could be overcome with a little thought.

In the final pic Dianne VK3JDI is working the winch with ease. A bit of the 20M 4 element monobander can be seen in the background. Also present is a very small cow, which appears to be trying hard to avoiding being crushed by the counterweight.

For the experiment I tried tilting the tower over without the counterweight and it did this with ease. Maximum strain was well within the winch specs and it held the load easily. The 5:1 gear reduction makes quite a difference to managing the load.

It is a good thing that the new winches can be operated quickly, because while the tower is tilted, my antenna for the wireless broadband internet antenna points to the ground, instead of to the base 5km away. Hence a couple of teenage kids have to entertain themselves while the tower is being serviced.

Also visible at the base of the tower are some 90mm, 45º pvc bends where all the coax cables enter the tower slab. They all come up through the concrete floor of the house some metres away. The 3 bends keep water out of the conduit, but can be pulled apart if the need arises to add more cables in the future.

Well, that’s it…Time to wind up this article. (or down as the case may be) Replacing a winch may seem like (and possibly is) a fairly nerdy way to spend a weekend, but if you make it easier to access your antennas, then you’re more likely to experiment with them. Also, on a stormy night you can ring up your loved ones from the hotel bar and get them to crank your antenna down for you - the ultimate test of a relationship.
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2 Metre Radios - April 2006
The Philips PRM8040 project
Well I think I have all but finished programming the Philips PRM8040’s

Here are a few “notes” about them.

When they are turned on, they look at their configuration, and if the head has been swapped, re-programmed etc, the head will come up saying it is “updating radio”. This will take about 30 seconds, this should not re-occur unless changes are made.
Some of the first radio’s I programmed were not “tested” with the head they ended up with, so you should see this once only.

The odd radio when first powered up will also think it has had some “calls”, just press the “que” button, and then you should see an option to erase these “calls”. The radios have the ability to sel-call each other, so that when you return to the car etc, you will see a message saying you have been called. I have not programmed in this option.

The heads have a “memory key” slot in them, this is a propriety Philips thing, they have been priced at $30 – Probably not worth worrying about.

Many of the radio’s had been modified with an extra connector hanging out on a length of speaker wire from a notch that had been “melted” (butchered) into the case, this connector is a white 2 pin unit, identical to the one’s used for the speaker, after hearing a “not very smart” comment from a club member, I started removing this mod before someone blew up their radio. There is probably the odd one in the first batch I have not removed. If yours has one, open up the radio and snip it off before the smoke gets out.

These radio’s were built in the Philips factory for 12.5KHz channel spacing, and don’t really like seeing deviation over 3.5 KHz. Normally a 12.5KHz channel radio will not see anything over 2 KHz, however some amateur sets when pushed can hit 5KHz. The only real cure for this is to change the crystal filter from a 12.5KHz unit to a 25KHz one. – Oh well, what do you expect for $40. If there is enough interest, we could get a pile of them from HyQ, etc.

Unfortunately I will probably not be at the next club meeting, you can try and give us a call on 7.070MHz, but his will have to be before the meeting as the band tends to die after 9:00, but give it a go anyway – use the bands or lose them.

Paul VK3TGX
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2 Metre Radios
The Philips PRM8040 project
Currently I am over half way through re-programming all the radios. Almost all the “complete” radio sets have been done, and I am now well stuck into the “incomplete” radio sets. Don’t worry about the “incomplete” tag, it just means they are missing a speaker mounting bracket etc. Of more concern is the faulty pile that now stands at 5. One of these is an easy fix, a new protection diode as someone either connected the radio to reverse polarity, or more likely connected it to a 24V truck without a 24 to 12V converter.

As we only received 48 heads, not 52, we have 4 spare radio’s so to speak, so hopefully we will have 48 usable radio’s to cover the list of requests, that now sits at 33 (last I heard). Lets just hope for no more faults, especially heads.

The channel programming I have been using is largely based on Ian VK3BUF’s FM92 program he devised several years ago, so if you are familiar with certain channel numbers, they stay the same. I have added a lot more simplex channels, so you can continuously tune from 144.500MHz all the way to 147.975MHz.

If the radio is run in “text” mode (default) then all the simplex channels of Ian’s original ’92 ROM and my additions are all sorted in order, with the exception being 146.225, because I labelled this channel as “GGREC CLUB”.
All the radio’s are basically programmed the same, except for some minor tweaks I have made along the way. Involving the labelling of muti-repeater frequencies etc.

Two of the radios have been loaned (not given) to Adam so some real world testing could be performed. (After all, if he didn’t open his mouth, we would have no radios). Anyway, all seems good so far, my programming has not confused him and his audio sounds, well, “Philips”. The last thing I wanted was to have 48 radios handed back to me with the comment of “they work, BUT ….”

At work, I found a service manual for a Philips PRM8030, same radio, different head. So, apart from the head, we have full schematics and alignment procedures.

Also in the kit of bits were GPS receivers – Hmm, hook up a display and bung them into your car, or how about use on fox hunts, or set up an APRS system.
DC power converters, 9-18V in, 15v (13.8) out, charge car battery from another battery! Radio modems – not sure yet – maybe just bung them onto eBay.

(Please note that no decision has been made on these extra items as yet. However, we will be looking to sell most of them given that we ended up a few heads short! A decision should be made at the next meeting. If you are interested in some please let us know. Andrew)

Paul VK3TGX

IRLP Repeater
Our new IRLP repeater had been sent up to Andy Beales in Queensland for some modifications. Thanks Andy!. At the committee meeting Albert reported that the repeater has been programmed and tests OK. Output has been boosted to 25 watts. It is on the way back to us.

We will also be sent a manual for us to copy and return to Andy.

Discussion took place about trying out the repeater at Alberts place to see what the coverage is. Access tone is to be changed to 123 Hz, to fall into line with the other repeaters. WIA & ARV (that’s Amateur Radio Victoria not Ivan) to be notified of the change to 123 Hz.

Hopefully we can have it all up and running soon.

Any concerns/comments should be made at the next meeting.
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Comet Duplexor - this might help!
I always like to share amazing discoveries in AR, although I might be the last one to discover the discovery.....??????

I had found that my comet duplexor that I purchased at the Hamfest was not operating properly all the time but it would come good and then I went along until the next time it operated in an erratic manner.

Today I looked further into the problem and found that at least on 2 meters, 10 watts at minimum is required to get the thing working and that makes sense when you think about it; In fact obvious. I would say there might even have been something in the instructions about it but I never read them.

The part is most useful for connecting a 2/6/70 antenna to a radio with 6 + 2/70 input. So at the risk of looking like a dill, I provide this info so someone may benefit from it. I suspect the inductive networks only function with enough field/Power. Like Hybrid Network in telecom cct etc.
73
Bill
VK3DOU
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Reviving Sealed Gel Batteries (Peter Woodland VK3KCG)
The Gel battery is well suited for use by amateurs to supply backup power in the event of a mains power failure. There seems to be a lot of these batteries around at the moment and the second hand price is very cheap. Most of these batteries are removed from service when they start showing a fall off in capacity and thus turn up on the surplus market. The best thing about these batteries is that they do not emit much gas if any when being recharged correctly. Recharging voltage should be 14.05 volts with an absolute upper maximum of 14.40 volts. Charging at a higher voltage causes the silica based electrolyte to swell and cause plate distortion. This renders the battery useless in a very short period of time.

The gel batteries are sealed and can be placed in any operating position as the gelled electrolyte stays locked between the battery plates and does not move. To revive a battery that shows loss in capacity due to the terminal voltage falling rapidly on current draw you must first get into the battery. The vent caps on most batteries can be popped off with the help of a screwdriver and the actual vents can be unscrewed using a correct size spanner. Once the vents are taken out have a look at the top of the plates to see if they look dry or moist. In most cases they will look dry.

The revival of the battery is pretty easy, just add distilled or de-ionised water so that it covers the plates by 10mm. The trick is to now load the battery so that after an hour or two the voltage discharges to 12 volts. Let the battery rest at this level for a couple of hours and then recharge to 14.4 volts. Check the water to see if it has been drawn into the electrolyte. If you have a millimetre or two on top of the plates then you have revived the battery. If the battery has taken all the water then add more water and repeat the process. Put the vents back into the battery and glue the vent cover back on with a few dabs of hot melt or epoxy. The battery capacity will improve over the next few charge discharge cycles


A picture showing the open cells, the question is can you see the picture???
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Lithium Ion Batteries – Tasty But Deadly
By Ian Jackson VK3BUF
There are lots of new electronic products out there which include Lithium-ion batteries as a power supply. But for all of that, not a great deal is known about them. They have become popular because of their high energy density. That is to say that you can jam a lot of energy within a very compact area, for very little weight. This makes them ideal for portable transceivers, cell phones and digital cameras. Almost twice the energy for half the weight/volume as traditional nicad cells. They also have really low self-discharge rates. (about half the rate of nicads) which makes them great for ‘emergency standby’ equipment.
However, if you are thinking of getting some to stuff into an old radio or appliance, then think again. They are a bit of a bugger to charge. They don’t behave the same way as any of the regular rechargeables, so put your old charger away.
* For a start, you can’t charge them until a certain terminal voltage is reached, like most other cells. A nominal 3.7V cell should be charged to a 4.2V rail, but it will reach that voltage level and still only be half charged!
* If you apply too high a terminal voltage you will permanently blow an integral over-voltage fuse inside the cell.
* If you charge at the right voltage, but for too long (such as with trickle chargers) the internal chemistry moves around and Lithium finishes up re-plating itself on anode, followed by internal gassing and (ultimately) fire.
* You can’t fast-charge them. Chargers that say they can, usually only achieve a 70% charge at best. (Typical charge times are 3 hours)
* They should not be charged in sub-zero temperatures, or beyond 45º. (at 100º they will blow an internal safety fuse)
* If you over discharge them, they will have a very short life. (never take the cell voltage below approx. 2.3V )
* You can’t measure state-of-charge by measuring terminal voltage. The voltage varies too much with ambient temperature and individual brands of cells.
(rule of thumb ~ 3.7V is roughly a half-charge, but don’t put money on it!

So, after that list of ‘don’t’s’ you may well be wondering how they are charged.
The trick is to manage them with a microprocessor so that the average punter can do their worst, without exposing the cells to harsh conditions. A cell should have 4.2 volts applied, then take a snapshot of the incoming current level. Keep on charging until the current demand has fallen to about 10% of the originally applied level, then halt the charge. The micro should be monitoring output current and voltage and temperature to prevent excessive charging & flattening of the cell.
Most modern appliances designed for use with Lithium ion cells have an integral microprocessor to manage all of this for you. Just be warned that if you try to replace them with nicad/NmHi/lead-acid or dry cells, or conversely, if you put a Lithium ion cell into an old appliance, be prepared for a dishonourable discharge.
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