4 Silicon chip Australia’s electronics magazine siliconchip.com.au
Amateur radio could be useful
in emergencies
David Williams (Silicon chip,
March 2019) is spot on when he ob-
serves that we have all been put in
a very vulnerable position since the
NBN was introduced.
As well as questioning how long all
the battery backups will last to keep all
this internet-based infrastructure go-
ing in a disaster, he asks how long the
phone towers will continue to operate.
But there is another problem with
relying on the mobile phone network
in a disaster scenario, and it’s that the
towers can be overwhelmed with calls
in these situations, making the net-
work virtually unusable. This leaves
absolutely no communication left for
victims to call for help.
Communications between emergen-
cy services and dispatchers has im-
proved considerably from the disas-
trous days of the Ash Wednesday fires,
when my amateur radio colleagues had
to liaise between emergency vehicles
with incompatible frequencies.
Since then, I have seen a general
loss of interest in radio transmission
as even some of my colleagues have
moved their communications to chat
rooms on the internet.
Here in central Victoria, members
of the Bendigo Amateur Radio and
Electronic Club (BAREC) have real-
ised there is one thing that will always
work when everything else has failed,
and that is radio transmissions pow-
ered by batteries.
To this end, we are now training
members of the public, who live in
remote areas, to pass the basic Foun-
dation Amateur Radio Licence which
allows them to communicate with re-
peaters and monitoring stations out-
side the danger area. We’re told that
they now feel a greater sense of secu-
rity and connectedness.
And of course, they can then use
their new found skills to explore the
hobby further. Silicon chip has cov-
ered radio and antenna projects before
and it would be fantastic to see more
of that in future.
Tony Falla, VK3KKP/G8HIM,
Castlemaine, Vic.Design flaw in Adjustable
Active Crossover PCB
I have found a problem with the
latest RevD version of the PCB for the
Adjustable Active Crossover (Septem-
ber-October 2017; siliconchip.com.
au/Series/318). If you power it from
a centre-tapped mains transformer,
when you switch the power switch
S1 off, the two transformer windings
are shorted out.
I was initially puzzled because the
unit seemed to work perfectly, but al-
ways had a blown fuse when I next
went to use it.
The short circuit designed into the
board took me some time to find! It’s
because the front two pins of switch
S1 are connected to a large section of
copper on the board. This is clear in
the image of the PCB pattern on pag-
es 70 & 71 of the October 2017 issue.
With a bit of difficulty, I desoldered
my switch and cut the front two pins
off it. This turns the switch into a DPST
version, and prevents the normally
closed pins from being shorted to the
centre pins when the switch is in the
off position. The two plastic struts
align the switch anyway and keep it
in position.
Other than that, this was a great pro-
ject to build and allows some interest-
ing experimentation with speaker de-
signs and audio electronics. I recently
acquired a new Keysight EDUX1002G
DSO, and its frequency response anal-
ysis function showed that the mark-
ings for the cross over adjustments are
pretty accurate.
Stephen Hockey,
Rosanna, Vic.
Response: sorry about this oversight.That large area of copper was provided
to help anchor the switch firmly to the
board when soldered. It should have
been separated down the middle, to
prevent the switch from shorting out
the transformer when off. This has
been fixed in RevE, and we will have
RevE boards available for sale soon.More preamplifier inputs wanted
Your magazine always provides
articles and projects of interest. For
some time I have needed a multi-in-
put preamplifier; however, your 2007
and 2011 designs only cater for three
inputs. Fortunately, I stumbled on
the October 2005 Studio Series ste-
reo preamplifier article (siliconchip.
com.au/Series/320), which provides
for five inputs.
Discovering that PCBs were still
available for that preamp meant that
it was all systems go! I have two dif-
ferent applications for the preamp, so
I have ordered two PCBs.
As the 2005 design specified
OPA2134 op amps, which are diffi-
cult to find and also are quite expen-
sive, I decided in place of them to use
NE5532s. The November 2011 article
is very interesting in the way it de-
scribes the performance differences
affected by different capacitor types
and values and methods for keeping
impedances low for good noise and
distortion performance.
I suppose the modern audio analysis
instruments that you have enable per-
formance improvements to be analysed
to a much greater level of detail than
was the case in earlier years.
On the subject, your Universal
Regulator Mk2 design (May 2015;
siliconchip.com.au/Article/8562),
while offering a lot of flexibility, does
so at the cost of forcing the builder to
restrict capacitor choice to 85°C types,
due to their smaller diameter. I much
prefer to use 105°C types for better
long term reliability, especially in ourLetters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that
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