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Mailbag

Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to "Ask SILICON CHIP" and "Circuit Notebook".

Sensor light with no manual over-ride

I wish to respond to the article in Ask SILICON CHIP, page 97, May 2007 (and the response in Mailbag, page 5, July 2007), regarding sensor lights staying on due to intermittent power glitches.

There is an HPM brand sensor, model 630/3A, that is set-up to work in sensor mode only, with no built-in manual override (note: the 630/3 has the built-in manual override). Power glitches, brownouts or switching the power off, then on again within two seconds doesn’t affect it.

If you wish to install a manual override on the 630/3A, you can simply add an external bypass switch.

Tony Cassaniti,
Garden Suburb, NSW.

Satisfaction with Nixie clock

I just had to let you know that the Nixie Clock published in the July & August 2007 issues is the best kit I have ever built. It took me about 10 hours to complete and I was very careful to ensure correct alignment of the various components.

My wife is so pleased and impressed by the Nixie Clock that she has made room for it in one of her glass display cases. The clear Perspex case really does make the Nixie Clock look incredible! Congratulations to David Whitby and SILICON CHIP!

Dave Sargent,
Howard, Qld.

Simple tank indicator has drawback

The simple tank water level indicator presented by John Williamson in the September 2007 issue does indeed perform exactly as he says. However when I tried the very same idea a while ago the problem I had was that the water in the clear plastic tubing was then exposed to sunlight and began to grow some multi-coloured algae which I decided I didn’t want in my drinking water.

Tony Ullman,
Georgica, NSW.

Comment: good point. The tube must not be exposed to sunlight.

Reason to invert a laptop display

I have been looking for a way to invert the screen of a laptop for about a year. I tried Google, online forums, etc and eventually gave up.

I therefore read the Serviceman’s Log for September 2007 with great interest. It presented an easy solution to my needs.

Interestingly the Serviceman could not think of why anyone would use this. In my case, the application is to mount an old laptop upside down on the roof of my 4WD and use it to display navigation with a GPS and as a large roof-mounted DVD player.

Tony Wise,
Melbourne, Vic.

Climate change scepticism

There has never been any doubt that the publisher, Leo Simpson, stands on the conservative side of the political spectrum but I would call him a climate-sceptic rather than "denier" and some hard-nosed scepticism is certainly needed with some of the self-serving "solutions" on offer.

Changing the area lighting on a block of flats to CFLs saved considerable power but the biggest impact was from the longer life, meaning that visits from an electrician at $80 per blown light globe were cut to one-third, never mind better lighting. The much higher cost of the CFLs was recovered in only a few months.

I’ve installed and maintained some remote area solar power systems and I agree that they are quite uneconomic where mains power is available. There are still large gains to be made in household energy integration such as waste heat recovery from fridges.

The economy of solar-electric panels is reduced by charge regulators that simply disconnect all those expensive watts, rather than redirecting them to the fridge and homestead water pumps in a load-shed tree.

However, I am at a loss to understand your swipes at solar hot-water heating. If there is one thing that already significantly unloads the urban electrical system it has to be domestic solar hot-water heating. The daily shower gobbles a surprising amount of energy.

But it’s not often that I get a good belly laugh from a SILICON CHIP editorial. After a couple of swipes at "environmentalists" (whatever that means these days), Leo Simpson goes on to demolish tree planting as a "net carbon sink".

Why I find this funny is that this very argument has been a mainstay of the native forest logging industry (misquoting a CSIRO study). Only a few years ago, it was "environmentalists" who were being derided for saying exactly what you go on to say – the mature carbon-sink trees would then have to be somehow totally removed from the eternal carbon cycle! That makes you as green as a "Forest Feral" Leo.

Sadly, the arguments for CO2 as "landfill", electric motoring and the nuclear fuel cycle still need similar cold scrutiny. In contrast, geothermal power looks very hopeful at this point, not least because the "waste" is not the stuff of parental nightmares and terrorist dreams.

Roly Roper,
Ivanhoe, Vic.

Solar hot water systems should be booster-free

I have two comments on Peter Seligman’s recent articles on how to cut greenhouse gas emissions. Firstly, concerning renewable energy from the electricity grid, when the renewable energy source is not generating, there is no electricity available from that source. Quite obvious really, so your energy consumption must fall to zero; ie, the light should go out.

If it doesn’t, it must be coming from a non-renewable source or some form of magic! Worse still, a fossil fuel machine needs to be running, using fuel, waiting for the extra demand. This is known in the power industry as "spinning reserve."

Real renewable energy consumers don’t consume when the renewable energy is not there! Otherwise it is not renewable energy – it is a sham.

Secondly, concerning solar hot water systems, about 25 years ago I lived in Papua New Guinea and developed an interest in "alternative energy." My employer (Department of Civil Aviation) had numerous remote aircraft radio navigational beacons and many were solar-powered (photovoltaic with lead-acid batteries) and I had friends who were missionaries.

Most missionaries were in locations where there was no power grid. Some had no electricity at all and for others, diesel-powered generators met all electricity requirements.

Diesels have 40% or better full-load efficiency and could be a source of hot water from the "waste heat" in the cooling system. I never calculated overall efficiency but it would have come close to 50% at full load with the waste heat recovery factored in.

Unfortunately, no one ran their machines all day. (6:00am to 1:00pm, and 4:00pm or 5:00pm to 11:00pm was common). Cooking was usually solid fuelled (carbon neutral) and many stoves had a heating coil for hot water but this form of water heating is not really "waste heat recovery" and won’t work between meals!

Solar heating was a viable alternative. Experience tells me that with a sufficient sized collector and tank, there was no requirement for a "booster". Most Australian commercially available solar hot-water systems at the time were adequate in PNG. At my own home, I covered one or two of the three collectors in the dry season as the water was too hot! I think it must have been designed for Melbourne!

After some design research, it became apparent that these same systems had a plate surface area that was about one third of that required for Perth latitudes and the tanks were too small for the planned consumption. My conclusion was that solar hot water systems designed for Perth were too small, and deliberately designed to be "boosted!" As a corollary, solar hot water systems, designed for the installation’s latitude won’t need boosting and therefore will be truly "carbon neutral" in their energy consumption.

Hence, booster-free solar hot water systems are the correct direction for reducing greenhouse emissions in domestic installations. Consumers need to become aware of the difference and government needs to promote the value of such systems.

Alan Johnson,
Greenmount, WA.

New Australian Vintage Radio Society

Your readers may be interested to hear about the formation of a new vintage radio organisation. The Australian Vintage Radio Society Inc is a not-for-profit organisation dedicated to the preservation of our radio and radio related electronic history.

Meetings are held on the fourth Saturday afternoon of the month and visitors are welcome. Most meetings include a talk by a presenter with experience in the field of restoration or history and a display of radios and related equipment of the era.

Other services available to members include a bi-monthly newsletter, technical assistance, restoration workshops, a valve and component bank and a circuit diagram service.

Further details can be obtained by contacting the secretary at: Australian Vintage Radio Society Inc, PO Box 3099, Syndal LPO Vic 3150. Or visit our website at www.avrs.org.au

Warwick Woods,
President, AVRS.

50th anniversary
of Sputnik I

1957 was the year I started school and the year space travel commenced. October 4th 2007 was the 50th anniversary of the 3-week long flight of Sputnik I.

At that time, my father was working as a scientist in the CSIRO’s Radio Research Board (RRB) under Dr David F Martyn, based in the Sydney area. This research group was investigating the structure and behaviour of the upper atmosphere. The experimental side of this work involved transmitting radio signals up and observing the reflected signals returned. This meant that there was a selection of antennas, receivers and expertise available to receive signals from the first spacecraft.

One Saturday afternoon, Dad and I drove to a building in the grounds of the University of Sydney. I remember being in a room dimly lit by outside light through high-blinded windows. There were large grey equipment racks, some with dark knobs, glowing dials and lamps on front panels. I remember one with a round green CRT display. There was the dull red glow of valve heaters visible where there were no front panels.

On a work table there was an incomplete looking metalwork thing and some cylindrical objects with wire pigtails. I had seen a similar sight in a WWII bunker used by RRB near Camden Airport.

Various knobs were adjusted and then we waited, Dad attempting but failing to explain Sputnik to me. Then it started, "bleeep bleeep bleeep bleep". The explanations then became simpler. The sound was coming by radio from 90 miles above from the first man-made orbiting satellite.

My first thought was this was like many other bleeps I had heard while near equipment racks. But I then realised my usually unemotional Dad was keen to share both the facts and his excitement, about this scientific and technical advance.

My recollection is that Sputnik I was not visible to the unassisted eye due to its small size but that the final rocket stage was. However, Dad said, these didn’t pass over Sydney at dusk or dawn and so he couldn’t show it to me. I think the rocket stage was visible further south.

In the next month, on November 3rd, Sputnik II was launched. This was visible in the evening sky from my home. We saw its star-like appearance hurrying across the sky with its dog and, I assumed, bleeper.

Graham Harvey,
Toowoomba, Qld.

Comment: thanks for sharing your memories of Sputnik, Graham. It really does seem like a lifetime ago.

Refining the Studio Series Preamplifier

I have recently completed the Altronics kit for the complete Studio Series Stereo Preamp (SILICON CHIP, October & November 2005, April & July 2006) and was most impressed with the supplied parts and overall performance.

An article in the August 2007 issue of SILICON CHIP highlighted the superlative performance of the LM4562 op amp, even putting the OPA2134 (as used in the preamp) to shame! I purchased a quantity of the LM4562 and since it is a plug-in replacement, popped them in.

With the preamp connected to my AWA F242 Noise & Distortion measuring set, it was obvious that something wasn’t quite right. Probing with a CRO revealed 10-30MHz parasitic oscillations around both IC sections. Both amplitude and frequency were dependent on volume control settings. Some lateral thinking suggested that the op amp output feeding the volume control via 100-150mm of screened cable (and hence 50pF of shunt capacitance) was the culprit. While the OPA has a gain-bandwidth product of 8MHz, the LM4562 tips the scale at more than 55MHz!

The cure was quite simple: insert a 100-220W resistor in IC1a’s (and IC2a’s) output feeding the volume control. This is easily accomplished by lifting the "pot" wire on the PC board connector and inserting the resistor in series with the screened cable and connector.

I was unable to measure any difference in distortion (little wonder!) but the preamp’s total noise (20Hz - 20kHz, flat) was 6-8dB lower with the volume control at "max" using the LM4562 op amp; well worth $25 for two ICs.

I also did some work on the potentiometer drive motor. I purchased a dual 10kW ALPS Blue Velvet motorised pot (on eBay from Germany). However, I measured a considerable increase in output noise (still around -100dB) when the motor was activated. A few checks revealed that it was noise radiated from the motor body, not the DC wiring. Two turns of mu-metal "tape" around the motor body and secured with a cable tie removed the motor noise completely.

The supplied toroidal transformer in the Altronics kit was rotated to optimise the signal-to-noise ratio (SNR), there being a definite sweet spot. The measured SNR on the F242 in dB terms didn’t show any reduction but the residual noise improved dramatically from a buzz to a hum.

To find the correct orientation, the F242’s noise "monitoring output" was fed into an audio amplifier and the resultant noise (more like a raspy buzz caused by transformer stray leakage and/or magnetising currents and possibly the diode bridge switching transients) was monitored on a speaker. The toroid was gently (and carefully) rotated to null the resultant buzz (very obvious!) with the volume set to 50% – the most likely setting used. The final SNR was better than -105dB with a terminated input, the top cover in place and using the LM4562s.

Kit Scally,
Forestville, NSW.

Speedo readings not good enough

I have read the recent letters regarding car speedo errors. I find it quite disconcerting that manufacturers are permitted such a large error. If I go into a supermarket and buy 100 grams of product, I expect to get very close to 100 grams (maybe ±1%). I would be very displeased to find that I only had 87.273 grams.

As you state, it must be very frustrating for heavy vehicles with speed limiters set at 100km/h to be stuck behind a line of cars all doing 88km/h even though their speedos are showing 100.

Your correspondent Adrian Leake (SILICON CHIP, August 2007) asserts that odometers are calibrated to read accurately. My experience is that they read low. On several different 5km ‘Speedo Check’ zones my odometer read between 4.8km and 4.9km (2-4% low). A timed check of the speedo shows that 100km/h is indicated as 108km/h, a fact that I can testify can’t be too much in error as I drive on the highway with the speedo indicating just below the 110km/h mark (approximate needle width) and have never had a speed camera ticket although I pass a large number of cameras on various highways.

Surely it is about time that car instrument manufacturers caught up with the rest of the world and made instruments that indicate more accurately the speed and distance. Perhaps even radar or GPS technology would beat the old mechanical devices running off the transmission.

Bill Neumann,
Yeerongpilly, Qld,

Some stereo TVs don’t reproduce stereo sound

Much has been discussed over the years about picture quality of LCD vs plasma television sets. But I am not sure if people are all that concerned about the quality of the audio from their new whiz-bang TV.

I recently discovered that at least one model of a well-known brand LCD is incapable of producing stereo on all TV channels. It consistently delivers dual monaural – ie, exactly the same sound from both channels – on Southern Cross High Definition. The problem is also evident on ABC HD, WIN HD and PRIME HD but it doesn’t seem to be consistent.

I’ve checked three other examples of this particular model and this definitely seems to be not just a fault but a major design flaw in this TV. It could very well be that there are other brands and models with the same problem. My investigations have revealed that this model is incompatible with the various audio modes being broadcast (see http://www.dba.org.au/index.asp?sectionID=14).

So if you are concerned about the audio from your TV, then have a close listen. You might be surprised to find it is not performing as expected.

I wonder if people really do "listen with their eyes" and could be blissfully unaware of this problem.

Trevor Dalziell,
Symonston, ACT.

Are mobile phones a hazard?

Like many others in our industry over the years I have followed the debate over possible health implications associated with using mobile phones. My background included control, communications and radar from 10kHz up to 20GHz so I think I have sufficient knowledge to comment from a perspective of over 40 years. Recently, a thought occurred to me on the phone issue and I would like to put it out there for discussion.

Phone studies seem to vary from maybe there is to maybe there isn’t a problem. In a similar manner to Scandinavia enforcing stringent standards on the zoo of signals associated with CRT monitors, perhaps it is time to examine how the phone studies were conducted and whether they were appropriate or sufficient. Some studies were based on statistical analysis of epidemiology data. Results were sometimes significant, others not conclusive.

I am cynical about any establishment and their ability to spin a story to put the best face to protect their interests. It occurred to me that physical studies were undertaken but very little detail of such tests is available. The thought was, "Did the test take into consideration close proximity of the mobile phones to the head?" I had been of the view that signal levels were at such a low level that the risk was higher from base stations. I did also consider a possibility existed that the pulse nature of the signal had an ability to force resonance and perhaps cause problems with some molecules.

We traditionally think in term of far field radiation and not the near field where the signal is launched, as is the case for mobile phones. Wavelengths used for mobile phones ranges from about 30cm down to about 5cm for some cordless phones. Purists will argue about the transition phase from near field to far field but for general discussion the conventional value of half a wavelength is sufficient. The near field for 900MHz phone services half is about 15cm and covers most of the brain cavity. This is also a problem for cordless phones at 25mm but less so.

In the near field, the magnetic component predominates and this is the issue that occurred to me. The near field being a magnetic field must interact with our blood due to its iron content. I would be interested to know if this has been considered. Any data obtained needs to reflect near field locations and not more conventional far field locations. Suitable data that may be available from radiography but such data would reflect a steady signal as compared to a predominantly pulse signal. Also the phone "duty cycle" would be higher. Have the hard yards been done or is part of our industry conveniently sticking its head in the sand?

Am I a technophobe? Far from it. It is important that we discuss such matters in a dispassionate way, unlike emotional mainstream press coverage. As technologists, we know that at some level hazard conditions start. Would a biologist studying radio illumination of a biological test subject even consider or be aware of the difference between near and far field conditions and possible differences in outcomes?

Brendan Falvey,
Gundaroo, NSW.

SBS is available from satellite

In the September 2007 issue on page 99 there is an item about poor UHF TV Reception from W. M., of Lesmurdie, WA. His problem was that he was unable to get SBS clearly in Perth, despite being just 6km from the transmitter.

My suggestion is to get either a 65cm or 85cm satellite dish and get SBS Free-to-Air (FTA) off the Optus B3 satellite with an FTA satellite set top box. Have a look at Christian Lyngmark’s Lyngsat website (http://www.lyngsat.com/optusb3.html) which shows what is on all satellite TV feeds.

Also, have a look down the bottom of Optus B3 list and you will find Free-to-Air SBS with a KU spot beam over WA.

Tony Liolio VK2ZLT,
via email.

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