Bredhurst Receiving and Transmitting Society
This section is all about helping you to remember the dangers areas there are in the hobby and how to try to avoid accidents. Now that you have come this far into the hobby we don't want to lose you !!
There is no revision section for this part of the course.
9a.1 Recall that a soldering-iron stand must be used to avoid skin contact with the hot bit of the iron when not in use.
Understand that soldering work benches must be well ventilated to avoid inhalation of solder fumes, which can cause breathing problems particularly to asthmatics.
When soldering fumes are given off from electronic solder which is a special type of solder which is called "cored" solder. The core holds the "flux" which enhances the cleaning of the surfaces to be joined. The flux when it becomes hot burns and gives off a vapour which should not be inhaled as there is the possibility of it causing breathing problems including asthma.
Understand that eye protection must be worn when soldering to prevent solder from splashing into the eyes.
9b Use of hand tools
9b.1 Understand that screwdrivers, drills, saws, and files must be handled with care to prevent cuts to the hands and face.
"Why do we have to understand the dangers of hand tools ?" - Asked a student the other evening. The answer is that the possibility of carrying out construction of your own equipment, even in a small way is now becoming a practicality, so this is a general introduction to the dangers of the most common of tools etc that might be used.
9b.2 Understand that any items being drilled, sawn or filed must be securely held in a vice or similar device to prevent them slipping or rotating.
9b.3 Understand that the chuck key must be removed before using a drill to prevent the key being ejected at high speed.
9b.4 Understand that using a centre punch will prevent a drill bit slipping.
9b.5 Understand that eye protection must be worn when drilling to prevent eye damage from small metal particles (swarf).
9b.6 Understand the reasons why a bench-mounted pillar drill is safer than a hand-held drill.
9c Working at heights
9c.1 Recall that a ladder should be used at the correct angle (4:1 height-to-base ratio).
9c.3 Understand why it is important not to overreach from a ladder, to prevent falling off.
When you are on a ladder remember another golden rule :-
"Always have three limbs in contact with the ladder"
that will prevent you from over reaching. If you do over reach a ladder at least two things could :-
9c.4 Understand why a tool belt or similar device to carry tools should be used, and that it will help prevent falling objects.
Understand the need to wear hard hats when working at height or when others are working at height.
9d.1 Recall that a dangerous electric shock can result from antennas and ladders coming into contact with or arcing from overhead lines.
You were introduced to dangers associated with electricity (mains) and (RF) in the Foundation Licence and whilst normally it is our friend to power our radios there is the dangers of electric shock can result from antennas and ladders coming into contact with or arcing from overhead lines. The potential arcing to occur is due to the ladder being at lower potential, that of the ground, than the voltages being carried by the wires and for the potential desire to flow into the lower level.
So don't try to erect :-
9d.2 Understand that a fuse must be correctly rated for proper protection, and be able to select an appropriate fuse using the formula for power, i.e. current = power/230, where 230 is the nominal mains voltage.
To re-cap mains plug fuses in UK come in three current ratings 3, 5 and 13 amps. The fuse rating that you chose will be the one which is just higher than the calculated value of the input current which has been worked out from the input power.
9d.3 Understand that a residual current device (RCD) will give better protection against electric shock than relying solely on a conventional fuse (which only protects against excessive current) and earth system.
NOTE: The student should appreciate that an RCD will detect currents to earth of about 30mA whereas a fuse will only blow at several amps and only when the fault is a short circuit ( L-N or L-E). The mechanics of RCD operation (differential current sensing) is not examinable.
Some students ignore this section maybe it is because they doe not understand that in most residential accommodation the residual current device (RCD) is used and thus is common place but not understood as was the old fuse wire.
The residual current device (RCD) is a modern device that switches off the power if a short circuit or overload occurs. It offer better protection again shock than conventional fuse as it shuts down much quicker. Fuses tend to have about 50% load extra to fail but this is only a generalization to help you remember the RCDs are better.
A short circuit ( L-N or L-E) Live to Neutral or Live to earth is all that the fuse in a plug can detect!
9d.4 Understand that large or high-voltage capacitors can store dangerous electric charges and must be discharged before working on equipment.
A capacitor has the ability of store a charge equal in voltage to that which is applied to "charge up" the capacitor. Which ,if some means to discharge the capacitor, such as a "bleed" resistor, does not exist, the capacitor might well stay charged for a long time until natural leakage of the charge occurs. If the voltage is 230V then the shock you would get from it would be the same as a mains electric shock. The danger would be even greater if it was a high voltage capacitor and a high value capacitor as the discharge would be immense.
Even a high value capacitor at low voltage say 12V could do a lot of damage it say a screw driver fell across it. It would be like a welding flash and probably burn the screw driver in half.
9e.1 Recall that the main health effect of electromagnetic radiation is heating of body tissue.
What is electromagnetic radiation please ? asked one student the other night. So here is the answer:-
As a Foundation Licence holder, if you have been operating your transceiver then you have been using electromagnetic radiation. In fact when you have been listening to the broadcast radio, watching the television or even cooking in your microwave cooker you have been using electromagnetic radiation one way or another. Electromagnetic wave is just a fancy way of saying radio waves but there are also many other wave that have names within the range of electromagnetic radiation as shown in the diagram below.
You can see now the change in frequency from say 1MHz at the radio to many many many Mhz at the gamma ray end. Note also the portion of the microwave just above radio and below infrared. Infrared is heat rays and microwave cooker do just that with slightly lower frequencies.
The only difference in the waves is their wave length.
So now you understand what electromagnetic radiation is the point here is to know that the main health effect of electromagnetic radiation is heating of body tissue just like you cook in a micro wave. Thus do not touch an antenna when in use and also do not get too near to them.
9e.2 Recall that guidance on safe levels of RF radiation is available from government and international bodies (HPA - Health Protection Agency and ICNIRP International Committee on Non-Ionising Radiation Protection).
Booklets can be obtained that give information as to what are considered "safe" radiation levels. Such booklets are available from government and international bodies (HPA and ICNIRP).
The HPA Agency (Health Protection Agency) was established as a non-departmental public body, replacing the National Radiological Protection Board (HPA) and with radiation protection as part of health protection incorporated in what is has to control.
So be aware that this change may not have filtered through to all training courses.
9e.3 Recall that it is unwise to look down waveguides or to stand close to or in front of high-gain antennas as they may be in use.
What is a waveguide please ? asked one student the other night. So here is the answer:-
Hi-gain antennas are yagis where the RF is being concentrated in one direction (for the most part) and thus it is unwise to stand in front or near to the side off a yagi as the ERP will be several times as great as the power being fed to the antenna.
Further the higher the frequency the greater the risk.
Note Yagi are usually fed by coaxial feeder and thus are not to be associated with wave guides as a feeder to them.
So stand clear of ALL yagis and especially those
at higher frequencies.