Norcim page 38.
Vintage technical data of Micron Radio Control systems UK 1974
Many apologies for the sporadic layout of this page as it is
being assembled from archive documents and copies that have been sent in from
the Micron model users of yesterday.
Micron was one of the first UK radio control
providers to use ‘Frequency Modulation’ on the 27MHz band. The problem of compatibility working alongside AM systems of the
time prompted use of ‘Automatic Gain Control’ in the circuitry. This
unconventional approach worked well providing no interference from the AM transmitters
of the time. When the 35MHz model control band was first introduced in the UK
in 1980 there was a mixture of AM equipment and FM equipment imported. Although
the Micron receiver worked well in its 35MHz form, most other FM receivers did
not tolerate the mix. The distinct advantage for Micron was very short-lived
however as 35MHz AM systems were quickly banned, leading to a FM only 35MHz
radio control band. The 27MHz FM version was kitted in two versions. A standard
version without the 455KHz filter ( a capacitor was fitted in its place) which
complied with the 50Khz spacing of AM systems of the time. A Professional
version was also offered which included an expensive 10Khz Murata filter giving
10KHz channel spacing capability complying with the new 35MHz band.
David Caudrey has reverse engineered a
vintage sample of the unique hybrid Micron FM receiver sent to us by Mr Bob Everitt (Thanks Bob!). The following circuitry shows how
Micron used existing well tried circuitry together with a TAA661 FM chip.
Micron 27MHz FM Receiver June 1978 Micron decoder
for 7 servos June 1978
This Micron 27MHz FM
transmitter of the late 1970’s gave much
thought of how UK model aircraft could be controlled on the new 35Mhz band of
that time.
Both AM systems and FM systems on 35Mhz were
imported of good quality, only to find that the new FM type systems could not
work alongside the older AM systems.
(Except the 35MHz FM hybrid Micron receiver which had no
problems working alongside the new AM transmitters).
At that time I looked at the new 35MHz AM
transmitters imported to the UK on a spectrum analyser and found that the
channel spacing was of exceptional quality, And well within the 10KHz required.
(The picture is of Bob Everitt’s
transmitter which he home-built in 1978 from a kit).
The problem was that the later breed of FM
receivers using chips of the day were not capable of tolerating a close by AM
transmitter of equivalent quality.
The powers that be decided that the easiest
way out of this dilemma was to Ban the use of AM 35MHz transmitters in the UK.
A sad decision for the development of the new
35 MHz band at that time as it resulted in complete chaos. UK manufactures and
even imported FM manufacturers all made their own special plug-in crystals
which didn’t work with any other Radio Control System.! A total disaster for
the new UK dedicated radio control band.
Had quality AM 35MHz systems been allowed to
survive, then all manufacturers would have used standard ‘third overtone’
plug-in crystals, The combined quantities of standard crystals for all
manufactures, would have produced a very significant reduction in price of
changing frequency spot.
OK, I know, it’s one of those ‘In Hindsight Moments’ but worth a
thought or two. Perhaps?.
Moving on now...
The following picture is of a 35MHz FM transmit
section component layout. It is a ‘fixed frequency’ type, meaning that only the
special manufacturers plug in crystals were used. The board could be home
assembled without having to be factory set to the correct FM frequency
settings. All frequency settings were fixed and determined by the plug-in
crystal.
The circuit for this RF section is shown on
page 3 of this website.
The following photo shows the copper side of the Printed Circuit
Board of the 35MHz transmit section.
The width of the copper (left to right of the print above) is 70
millimetres.
Another Change of
subject,
During the 1980’s a company called ‘Century
Systems’ arrived supplying a host of model electronic kits. One of these kits
was a ‘Battery Backup’ kit for use in the model aircraft. The idea was to
provide a second battery that could automatically be electronically switched
into use if the main battery failed, either with too much flight time or
perhaps failure of a single cell 
in the nicad pack.
David Caudrey has investigated
one of these units supplied by Bob Everitt and has reversed engineered the
circuit shown at the side
The reserve battery could be quite small,
capable of just one or two flights. So if a check was made before the next
flight to see which battery is being used, you could keep that flight, the
last, and short, if the reserve battery was being used. The small battery would
not add much weight to the model. On a good flying day, One would have four or
five power flights of about ten minutes so it would have been good in those
days (forty years ago!) to have the Battery Backup device.
The reserve battery is set to come in
when the voltage of the main battery has reduced to 3.98V. There is no going
back i.e. the main battery is not reselected if its voltage
recovers as it might well do off load.
At that time Century Systems were ahead of
things to come for model systems.
These days, drone transmitters begin a loud
bleep when the drone battery has just a few minutes of flight time left.
Technology has moved on.
MORE NOW ON THE INTRODUCTION AND DEMISE OF THE 35 MHz MODEL
FLYING BAND INTO THE UK. 1980.
During the 1970’s in the UK there were
several electronic kit manufacturers of radio control equipment including
transmitters, receivers and servos. Lots 
of fliers used this ‘home build method’.
At the end of 1970, the UK BMFA had
negotiated acceptance of a new ‘Model Flying’ radio control band on 35 MHz with
Ofcom. This basically was to get away from the 27 MHz band as it was shared
with an ever increasing use of Citizen Band radio by truckers and enthusiasts
and there was a safety problem.
The 35 MHz radio control band had been
working in the EU for a couple of years at this time without problems so a
similar set-up was implemented here in the UK. All the UK manufactures of the
time and Kit manufacturers had to have sample testing using an outside Testing
Facility to show that their transmitters could safely be used on the new narrow
band frequency spots just 10KHz apart.
Many UK manufacturers used the ERA (Electrical
Research Association) in Leatherhead Surry to test their products. They tested
the transmitter samples producing a report which included a Spectrum Analyser
shot and details of radiated RF output. The photo shows the output of the
Micron home build kit transmitter with the 10 KHz spacing ( like the photo of Bob Everitt’s
PL-7D transmitter above). The output was clearly well
within each 10 KHz frequency spot. Zero interference to both next door
frequency spots.
Unfortunately at organized Model Flying Events,
the organisers got the jitters about home built Radio (perfectly
understandable) and they often tried to allow the frequency spot each side of
the home built transmitter to be Free. The thinking was to ‘play safe’ for
interference. This often could not achieved on busy days and the owner could
not fly on that day. This thinking unfortunately filtered down to the many
flying clubs, producing animosity about home made radio gear with club members.
This was the tip of the iceberg for the
‘Soldering Set’, of the seventies. The people that had built their own RC gear
for almost a century. Home built gear became untrusted by the everyday club
flyer. So along with low cost imports, the enjoyment of building your own RC
gear came to its sad end . Also at this time several UK manufacturers of fully
assembled RC equipment slowly died because of the low cost imports. There are
now no UK manufacturers of model radio control equipment in the UK.
With the introduction of the shared 2.4 GHz
band, the special 35 MHz model aircraft band has now become a relic of the
past. All of the new 2.4 GHz model radio control gear and models are now simply
imported.
During the late 1970’s, most radio control manufacturers used
the Signetics NE5044 transmitter encoder chip. The
chip was capable of generating up to seven pulse width servo channels using a
lower component count of the traditional string of ‘half-shot’ circuitry. A
typical 7 channel circuit using the NE5044 chip is shown below.
The circuit uses the ‘fixed frame’ option
churning out up to seven servo pulses every 20 milliseconds.
To prevent interference from the strong RF of
the transmitter (moving servos off centre position) with aerial extended, the
PCB layout carefully covers the chip with copper from the PCB to alleviate this
problem.
5044 coder board component layout showing the
line of seven plugs at the bottom of the board.
The sockets for these plugs are from the
control joystick potentiometers.
Reversal of the sockets provide servo reversal.
The angled plugs in the centre of the board
are used for optional plug-in channel mixers.
This shows the copper side of the coder
printed circuit board
The length of the board (left to right) is 14
centimetres.
This
drawing shows the wiring of each of the two potentiometers in a standard
mechanical trim joystick used in Radio control transmitters. Reversing the
socket, reverses the servo.
The wiring is twisted together.
A PLUG-IN MIXER FOR ‘V’
TAIL, DELTA, FLAPERONS, COUPLED AILERON RUDDER, AND AIRBRAKE APLICATIONS:-
The circuit uses the popular quad Op-Amp
LM324 along with trim pots which vary the mix required. The board mixes the
first three channels for the different effects and should no mixing be
required, normal operation can be returned to by rotating all the trim pots to
one end.
The copper side of the mixer board is shown
larger than life. The length of the board (from left to right) is 8.5
centimetres.
BOB EVERITT SENT IN AN ORIGINAL DRAWING OF THE MICRON 27 MHZ FM
RECEIVER (SHOWN BELOW) the drawings in those days, March 1978 were so big that
this bit only just fitted our A4 scanner. However it shows how using the Murata
filter in place of a capacitor produced 10KHz spacing on FM. (This input
relates to the notes at the top of this page)
The transistor types used are
A type = 2N5457
B type = 2N3904, MPS3904, 2N4124.
A MILD CHANGE OF SUBJECT, OVER TO THE MODELS THAT OUR
ELECTRONICS USE ...
Mike Hausner sent us a mail about model flying of less than 250 grams flying
weight.
Hi Norcimguy,
I saw your info on "under 250 gm RC" and
thought I'd drop you a line.
Here in the US there is a small company that is
making a series of 250 gram models. He has 28 plus designs based on
older models and also sells the RC gear needed to fly them. They are
all laser cut kits.
Mike designed an electric powered
model called ‘Torpedo’ which was published by the Model Aviation Magazine plans
service. Recently Mike has done a Mini-Torpedo that conforms to the ‘Less than
250 grams model flying class’. You can fly this mini version anywhere! There are
no regulations involved. Just use your own thoughts of where and how safe is it
to fly. It should easily be accepted as a ‘Park Flyer’ like a Kite.
This is Mike’s pretty Torpedo
250 which certainly looks the part. I have yet to get the dimensions of the
mini-version but that fuselage side area should allow side flying without too
much problem.
Mike’s original ‘Torpedo’ design
was covered along with building details by the Model Aviation Magazine plans
service.
See https://www.modelaviation.com/mike-hausners-torpedo
Another Sub 250 Grams model.
David Caudrey’s
design called ‘Vega’ is covered in detail on page 33 of this website.
Some history now of how model radio control using FM started in
the UK during the mid 1970s.
David Caudrey has looked at one of the very
first 27MHz transmitters that used Frequency Modulation for the very first time
here in the UK. The Micron transmitter was available in electronic component
kit form, using supplied printed circuit boards. The kits included folded
aluminium parts together with abs plastic injection components to make up a
complete hand held RC transmitter ready for use at switch-on.
The original circuit comes next from DC.
Mike Meakin
was the guy that came up with how to produce FM without having to adjust the
frequency deviation (this would have required the use of an expensive frequency
Counter which most home constructors would not have) Mike’s idea was to use two
pre selected capacitors in series with the Tx crystal
(2 x 56p) and a simple transistor stage, switching one of the capacitors in and
out, via the encoder input. His idea was ideal for home construction as
there was nothing to adjust ! Totally within the technical spec of the day and
also including the later new 35MHz band for Radio control models.
Regards Terry and David