Vale Ray Kelly

I am sure that the Vintage Radio article on "Ray Kelly and the HRSA" published in the December 2005 issue of SILICON CHIP will have been of much interest to many of your readers. Sadly, Ray Kelly passed away on Saturday November 19th, 2005, some 23 years after he set up the HRSA.

He will be greatly missed by the many members that he so willingly assisted over those years.

Warwick Woods, President,

Historical Radio Society of Aust.

BPL will be carefully regulated

It was with some concern that I read your editorial on BPL in the November 2005 issue of SILICON CHIP. BPL has evolved over recent years and in its current format it operates in the USA, Europe and Asia within regulated standards. The Australian regulator, ACMA, will ensure that the same standards apply to any deployment of this or any other technology in our country. Otherwise they will simply refuse to license it.

Also, it is no longer utilities alone that are involved in BPL. The largest investors in BPL are Google and IBM and Intel has recently taken a leadership role in this technology as well.

In addition, I take exception to your claims that the IT organisations, the utilities and the regulators have not thought through the issues that you outline in your editorial or that these utilities would be able, in some way or other, to influence our highly-regarded regulators in Australia and elsewhere. These regulators are independent and are quite capable of making their own decisions on these matters.

I am concerned that the tone of your article could generate unnecessary anxiety in the marketplace. There are no plans anywhere in the world that would see nationwide BPL deployment. At best, BPL might take 10% of overall broadband penetration. Its key markets would be in regional deployment and on the edges of cities, where fixed telecommunications networks are less economically viable.

Furthermore, it is quite possible that BPL is an interim technology, bridging the gap between the current inadequate copper-based networks (which are often unable to deliver true broadband services, especially in regional areas) and the Fibre-to-the-Home networks of the future.

Nevertheless, there will always be areas in Australia where Fibre-to-the-Home will not be feasible and both wireless technologies and BPL will have a longer-term role to play in these markets.

Is BPL the final broadband solution? Certainly not but it is an excellent technology which at the very least should be considered for delivery of broadband to areas that otherwise would be under-serviced or not serviced at all.

I have organised three BPL Summits and I invited the radio amateurs to attend these discussions. In addition, upon my advice, they have also been invited to the various industry demonstrations, seminars and trials.

I had hoped the amateurs would take up the invitation to work with the industry to find solutions. Unfortunately, despite several appeals from me, they have declined to do so and their objective continues to be a total shutdown of BPL in Australia.

My argument is that even if BPL were to achieve a 10% penetration, it would take several years to reach that level, during which time there would be ongoing opportunities for fine tuning, reviews and other chances to get it right. Whatever happens, the possible (still not certain) interference to radio amateurs would always be limited, while the benefits to regional BPL broadband users would be enormous. For example, perhaps 1000 amateurs would be affected, while possibly 500,000 regional users would benefit.

I have great faith in our regulators to make sure that the appropriate decisions will be made regarding this technology, decisions which will be in the best interests of our country and which will take into account both amateur radio and the regional broadband users.

Paul Budde,

www.budde.com.au

Paul Budde is an independent telecommunications analyst and commentator. He is working with the utilities and the telecoms industry to develop better infrastructure-based broadband competition in Australia.

Old computers & printers great for components

I like the idea of your "Recycle It" column. At the end of last year, I collected a pile of old (386/486) computers and old printers from our local high-school. Many of the computers were completely unsalvageable and I had no real use for the printers apart from a little laser printer that works like a charm. It took me several weeks but after wrecking the machines I now have an enormous supply of components.

Components were lifted from the motherboards using a heat gun. The printers and a range of 5.25-inch floppy drives yielded a collection of stepper motors, gears and wheels. The old AT style keyboards supplied hundreds of little switches, some of which I have used by mounting them on a custom PC board and fitting them back into a shortened keyboard case. The keys were spray-painted and re-labeled. Using a PIC chip and the original coiled cord, I can connect these custom keypads to any circuit that can accept a serial signal.

At the moment, that means small robots which are driven using the stepper motors I harvested from the printers. I also have a huge assortment of connectors, piezo and dynamic speakers and ribbon cables which are used on the robots, and logic circuits, most of which of have tested OK. This is not to mention the dozens of LEDs from the computers and printers, as well as PC-board headers that also come in handy. Perhaps you could do an article on what you can get from old (older is better) PCs.

Tim Polmear,

Moora, WA.

Comment: we featured an article on this subject some years ago. As you have found, it is still very worthwhile doing.

Concerns about bilge sniffer

I have some comments regarding the Bilge Sniffer in the September 2005 issue. It is indicated in the article that the device is intended to be used in an area which may contain a flammable vapour (I accept that using this device might of course prevent a larger problem), however the device has no protection technique employed to itself (or the fans which you are proposing to attach to it) to prevent it being a source of ignition.

Such devices would normally have to be certified by a test house (LOSC/Test Safe in NSW, for example), to some sort of standard.

I would be inclined to at least consult and design the device around those standards even though it might not be tested to those standards. (I am talking about AS2380.1 through to AS2380.7).

At the very least, I would be inclined to have the hydrocarbon sensor located on a cable in the said potentially flammable atmosphere and have the monitor and its heat-generating voltage regulator and a relay in a known safe area. There are some other items that could be attended to, like making sure the hydrocarbon sensor is protected from excess voltage and current.

One really important thing to consider are the fans. Fans are a good source of ignition; they generate static energy and they have brushes, both of which are excellent sources of ignition.

It is not acceptable to push air into a cavity either, as this can disperse gas/vapour into other areas, and not just back outside. See also AsNZS3000:2000, page 212.

Alex Scott,

via email.

Comment: your points are valid but it must be said that the best source of ignition in a boat’s bilge is the engine itself. Without some sort of vapour alarm, it is a potential accident waiting to happen.

How to re-transmit a television signal

I would like to comment on your reply to the email from R. F. in the "Ask SILICON CHIP" pages of the November 2005 issue. The email requested information on how to re-transmit a television signal into a valley in which a clear signal cannot be received.

One thing you forgot to mention was that the transmitting antenna at the top of the hill should be in the opposite polarity to the receiving antenna at the top of the hill; eg, if the receiving antenna is horizontally polarised, the transmitting antenna should be vertically polarised. This is to prevent interference between the two antennas, and also between the original signal and the receiving antenna at the bottom of the hill.

I experimented some years ago when the new UHF translators were being installed on the NSW Central Coast. While receiving vertical and horizontally polarised signals with a Wissi EE 06 antenna and a field strength meter, it appears that for a horizontally polarised signal, there is a 25% attenuation between horizontal and 45 degrees and thence a 75% attenuation between 45 degrees and vertical.

The reverse is true for a vertically polarised signal. If memory serves me correctly, the rejection ratio between horizontal and vertical polarisation is in the order of 30dB.

Brad Sheargold,

Collaroy, NSW.

Active TV re-transmission system

Regarding re-transmitting TV signals (page 106, November 2005 issue), I have seen it done on UHF and with the antennas separated by at least 200-300 metres out of line-of-site to avoid positive feedback. I must stress the area has only a few houses - none on the "ridge line" - and interference to adjacent properties and services is (and must be) nil.

It is an active system, using a UHF-only masthead amplifier (GME is good) of 34dB gain at the four-element phased-array receive antenna with an in-line amplifier of 34dB gain at the re-transmit end.

The re-transmit aerial is a Yagi, with about 102 elements for maximum directivity and set so its polarisation is the opposite of the receive aerial.

A solar panel can be used so the system runs off 12V and be sure to get the injection point on the correct side of the in-line amp so it powers both amplifiers. Quad-shield low-loss cable helps. The reception at 400 metres from the re-transmit aerial is not perfect but is definitely watchable and could probably be honed for better performance.

If someone has a cheap channel-specific translator solution I’d also love to hear about it. They seem to cost in the thousands per channel. I’m sure it shouldn’t cost that much to guarantee frequency stability and a low level of emissions, etc.

(Name and address withheld

at writer’s request).

Long TV feedlines

A letter in the November issue asked about re-transmitting UHF/VHF signals to a house in a valley. Suggestions offered included two antennas and a masthead amplifier. There are other solutions.

Many years ago I saw a similar situation which had been resolved with one antenna at the top of a hill and over 500 metres of telephone line down to the house. I was assured by a local, who was a very competent radio engineer, that it worked extremely well.

The 600W pair (two copper wires about 150mm apart with a minimum of insulators and supports) was very low loss and in an electrically quiet location, absorbed little, if any, noise. I have also seen the technique used in a remote area where TV reception was reliable and noise-free in one spot and no signal whatever just 100 metres away (where the homestead was, of course!). Open wire feedline resolved this situation also.

At UHF, this solution may become rather lossy, however "open wire coaxial" feedline (I cannot remember the name of this) may be considered. The feedcones for this are a bit large for VHF but quite practical at UHF.

Geoff Syme,

via email.

Restoration of Ferrograph tape recorders

Owners of the old 1970s classic Ferrograph tape recorders have mostly discovered that all the rubber rollers and pinch wheels have turned into a gooey mess. Mine went this way recently and I have had the good fortune to locate a company in Tasmania that can recondition such parts using more durable materials.

The results are excellent and as most Ferrograph owners would probably read SILICON CHIP, I thought I would pass this information on. The company is Tasroll Engineering Pty Ltd, 373 Brightwater Road, Howden, Tas 7054. Phone (03) 6267 2585.

Graham Lil,

via email.

CO sensor and air-circulation modes

A couple of items in the December 2005 issue attracted my attention. The letter in Mailbag from Graham Goeby concerning "fresh and recirculate modes" in vehicle ventilation systems is quite correct in saying that the control electronics in modern cars will override recirculate mode to allow fresh air into the cabin, as this prevents the buildup of harmful gases. However, what about the large number of vehicles that do not have electronic control of the fresh/recirc system?

My car has air-conditioning but the fresh/recirc system is manual. Now the actuator is electrical over vacuum and the vacuum is supplied via engine manifold vacuum and a small vacuum accumulator which is located inside the left front wheel arch hidden behind the inner arch trim. This ensures very little loss of vacuum when the throttle is opened and the manifold vacuum is lost.

When I hit the recirc/fresh switch, a small electric motor operates the diverter flap and changes the fan air intake from either fresh to recirc or visa versa. This motor is also limited by two microswitches which are actuated by a single cam running off the shaft the flap pivots on.

Using the CO detector to activate the recirc flap is a very good idea. However, having the air system running on recirc when a high concentration of CO is detected is not such a good idea. Surely, running on fresh air would be better then running on recirc air and keeping the carbon monoxide inside the vehicle.

Although, if you were stuck in a traffic jam with the high concentrations of noxious gases present in these situations, having the air system on recirc would seem like a good idea but to be honest, it would only take a small breeze to cut the concentration of gases down dramatically.

In my opinion, using the air system on fresh during times of high CO concentrations is vastly better then recirculating the cabin air and only adding to the gases contained within the cabin.

High CO concentrations in the cabin when you are not stuck in traffic is a sign of a defective exhaust system and this needs to be addressed and repaired as quickly as possible, if not for the health of the driver, then for the health of the passengers. In the case of small children, even a moderate concentration of carbon monoxide can have a serious or devastating effect on the development of a small child, especially a baby!

Secondly, Russell Verdon’s letter about scavenging parts from old scanners drew my attention as I use an old scanner as a light box. Powering up the tube within the scanner was very simple and virtually every member of my family use this light box for one thing or another.

My children use it for tracing, my wife uses it for image checking and viewing slides and I use it when I am tracing circuit tracks on double-sided circuit boards, as it allows me to see both sides of the board and both sets of tracks at the same time. I can also see if all the through-board connections are complete and if all the component lead connection holes are free of debris and blockages. All around, it is a very useful piece of gear.

Dave Sargent,

Howard, Qld.

Comment: we take the view that the carbon monoxide sensor is very sensitive and warns the driver that he/she is driving into unsafe air. In practice, if you can smell traffic fumes while driving, you are inevitably exposed to carbon monoxide, as well as all the other noxious combustion products.

We think it is preferable to switch over to recirculation mode immediately CO is detected rather than to continue to unknowingly breathe traffic fumes for quite long periods. In fact, many people cannot smell traffic fumes at all and so they are always at risk. Of course, if carbon monoxide from the vehicle’s own exhaust is leaking into the cabin, then the CO sensor will also detect this.

If you have a headache after a long drive in traffic, it is a fair bet that you are suffering from carbon monoxide poisoning.

Cruise control is very handy

I read the lead article on adaptive cruise controls in the September issue. Cruise controls are very handy – we have one on our Volvo.

I had a discussion with a Bentley owner recently who said he would never use his as he was concerned he could have a medical seizure and not have time to brake. He is middle-aged and fit but it made me wonder. Maybe your staff have a view on this?

Ian McPherson,

via email.

Comment: our view is that cruise controls work well, except in heavy traffic, winding roads and on steep hills. If a person is so fearful of having a seizure, he should not be driving at all.

Flash point and volatility

In the Mailbag pages in the 2005 December issue, the letter on flash point and volatility would appear to be incorrect. Diesel has a flash point above 61.5°C, a vapour pressure of <0.5kPa and an auto-ignition temperature above 250°C.

Unleaded petrol has a flash point of less than -40°C, a vapour pressure of 35-90(reid)kPa and an auto-ignition temperature above 250°C.

Flash point of a flammable substance is the lowest temperature at which it gives off sufficient vapor to form a flammable mixture with air, so that on application of a flame the vapours will flash, but will not continue to burn.

I feel that the letter states that diesel will flash at a lower temperature than petrol which is not the case. If there is such a thing as a safer fuel, it would have to be diesel.

A look at the Shell website (www.shell.com) will confirm the above temperatures.

Bruce Edgar,

Rockhampton, Qld.

Comment: In practice, to quote from the Shell website, "Volatility characteristics vary on a monthly basis to provide good cold weather starting in winter and to prevent vapour lock in summer. Consequently, petrol should not be stored for long periods".