The Westlakes news broadcast is transmitted
every Sunday at 9am on
2 meters at 146.775
WARC News Broadcast 30-7-2017
The cold morning yesterday resulted in activity at the
club being slow to start. As the sun rose, however, and
the temperature started to thaw the western side of the
Lake, the number of members increased quickly. At one
stage yesterday afternoon most members at the club were
outside the shadow line of the verandah absorbing the
solar radiation on offer. Small groups gathered among
the vehicles in the car park sharing news of the week
and solving the problems of the world.
Ian, VK2FIGM, John VK2EV and Col, VK2YP were measuring
the characteristics of a 2 m Slim-Jim antenna, recently
purchased by Ian. Once appropriate adapters and charged
batteries were found for the antenna analyser the
antenna was found to have excellent SWR. Ian was
particularly happy with his purchase.
Barry, VK2FIN and Ken, ***** checked the Yeasu 707
transceiver recently donated to the club to see whether
it would be suitable for the Foundation Licence exams
next week. Although the receiver was working nicely, the
digital display on the set was not. Steve, VK2LW and
John, VK2EV then decided to look at other sources of
transceivers ‘with knobs’ for next week’s exams.
The winner of the meat tray was lucky Luke, VK2LGW.
It is already time to start preparing for this years
Annual Westlakes Field Day on September 17th. There's
already lots of great items on hand for the famous
Westlakes Auction where many a bargain can be had, and a
bumper raffle to be drawn on the day. Details to be
revealed next week and hopefully in the next newsletter
Another date for the diary is August 5th. It is hoped to
have an outdoor brainstorm and idea exchange on vehicle
antenna and radio mounting commencing at 1pm. The
highlight will be checking out a Landrover County that's
about to undertake an around Australia tip, and
advice/discussion from experienced members on the best
ways to install and maintain mobile equipment. The more
that can attend will mean the more ideas and knowledge
that can be shared. Like they used to say on TV, "Please
Foundations of Amateur Radio
The other day a whole new world opened up to me when I
came across the idea that Voltage is the same as Force
and Current is the same as Velocity. It all came about
when I installed two mechanical filters into my radio.
You heard that right, in my shiny solid-state radio, I
added moving parts!
The purpose of this was to improve the way the radio
ignores unwanted signals and as a result has an easier
time hearing what it is you really care about. The radio
already has filters built-in, but mechanical filters
offer a cleaner output with less distortion across a
wider range of temperatures. Another way is to say that
- mechanical filters have a much higher Q.
Think of a pendulum swinging through oil, it's losing
lots of energy for every swing and has a low Q. The same
pendulum swinging through air retains most of its energy
and has a high Q. The same is true for mechanical
filters, less energy loss, better reproduction, better
outcome for the things you want to keep and hear.
So how does this then work?
Turns out that our electrical theory with inductors,
capacitors and resistors have mechanical equivalents,
specifically mass, stiffness and damping. As I said when
I started, Voltage is Force and Current is Velocity.
It turns out that all the maths we use to design
electrical filters can also be used to design mechanical
filters and 1946 Robert Adler from Zenith did exactly
that. This worked so well that in 1952 the Collins Radio
Company started manufacturing them and today we still
use them in many different radios.
As an aside, you might be surprised to learn that the
first filter that Robert Adler invented in 1946 was for
a 455 kHz filter, which I could technically still use in
my radio today, since the same Intermediate Frequency or
IF is used.
The mechanical filter - vibrating bits of metal -
resonate with specific frequencies, much like a tuning
fork does, but your radio deals with electrons, not
movement, so the electrical signal is first converted
into movement by a piezoelectric transducer, a piece of
material that distorts when you apply an electrical
field and when you use it in reverse, distortion creates
an electrical field.
So, you have a box with a wire at one end and a wire at
the other and in between are two transducers and a bunch
of mechanical resonators, much like a string of pearls
on a necklace.
I mentioned earlier that mechanical filters have a much
higher Q. An electrical Q might range between 100 and
500, the mechanical Q in 1946 using steel was several
thousand and in today's filters using Nickel-Iron
alloys, a Q of 10,000 to 25,000 can be achieved.
Without going into the maths, what is this Q really
describing, other than the pendulum in oil and
One way to explain Q is to say that it describes the
"goodness" of a resonant circuit, the higher the Q, the
better the circuit. In our case, "goodness" means that
it resonates better where we want it to and not where we
don't want it to.
Before you start wondering, why the letter "Q"? Turns
out all the others were taken when K.S. Johnson was
looking for a letter to describe the attributes of coils
in 1920. Today we think of "Q" as Quality, but that's
the cart before the horse.
Anyway, back to Amateur Radio. If you look at a
theoretical filter, you'll see a lovely curve that lets
through the bits you care about and ignores the bits you
don't like, but when you then start looking at the real
world where damping and resistance come into play,
you'll soon learn that there are all manner of ugly
spikes on this lovely curve.
A typical tuned electrical circuit will have artefacts,
or distortions along the way, dipping down, instead of
staying straight, or having an ugly peak when it should
be smooth. This in turn results in something that you
can hear, distorted audio where low frequencies are
under or over represented and strange distortions
occurring along the audio range.
It also means that adjacent signals, the ones you're
trying to ignore get caught up in this same distortion
and you'll hear some of those when you don't want them.
So when I say that a mechanical filter offers a higher
"Q", it means a whole lot less distortion and a better
representation of what's going on. As an aside, in
transmit, a mechanical filter will also help contain the
energy coming from your signal and transmit it where
it's needed, rather than waste it where it's not
helpful. As a QRP station, every little bit helps.
I just love this hobby, every turn is another surprise.
I'm Onno VK6FLAB
Well that’s all the news from Westlakes that I have for