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Section
400 Content Consideration
This section deals with most types of power amplifiers used within the
EMC disciplines. Some of the amplifiers are a “two person lift” so be
sure to get help when manoeuvring them. Be sure that when you site
the amplifier on a bench or elsewhere there is adequate ventilation for
the cooling fan. Be also aware that although amplifiers may be listed as “x “Watts, the
manufacturer is guaranteeing that power at the start & finish of the
freq range. Actual output powers will obviously exceed this by up to 3dBs
in center of operating range. For the 50Watt & higher powered amplifiers
you will need a fully rated 13amp Euro lead with the indented push-socket.
These can be hired in section 700 if you don’t have one. If the amplifier
is feeding a load with an extremely bad VSWR to avoid possible damage it
will be necessary to insert a 3dB attenuator pad of the appropriate wattage
at the o/p of the amp. Some amplifiers have forward power meters but this
assumes a matched load to be meaningful. Some of the very low frequency
amplifiers have an o/p impedance in the order of a few Ohms and will almost
certainly need transformer matching. Apart from the main section covering
items 400 through to 430 there are a further two sub-sections.
The first is entitled Pre-Amplifiers. These are sometimes
known as signal amplifiers as apposed to power amplifiers and are primarily
used to boost the signal to noise ratio prior to entering a receiver or
spectrum analyser. Their amplification ranges between 20 and 40dBs, and
are mains driven although item 440 has an internal battery. Just check that
you have adapter compatibility between amp, coax & receiver. Adapters
and cables can be found in section 700. Each pre-amp comes with gain versus
frequency data. This will have to be entered into your software files if
using an automatic receiving system with your own programme. Such files
are already entered in our software if you decide to hire a laptop with
one of our receivers.
The final sub-section is Microwave Power Amplifiers.
So far EMC Hire is listing devices from just under 1GHz up to 18GHz
with o/p powers between 20 & 30 Watts.
NOTE: Extreme caution must be exercised by the end user
with devices exceeding 1GHz. If you are in any doubt or have not used these
devices before you must make this known to the hire department before proceeding.
Never look into or stand in front of a microwave antenna or horn.
Make sure the area in front of the transmission antenna is clear of all
personnel before switching on. If more than two personnel are involved in
the operation of the field generation, then the person in charge
overall must control the switch-on/switch-off procedure of the signal generator
feeding the microwave power amplifier.
Microwave power amplifiers take the form of both solid state & travelling
wave tube amps. Be especially aware of poor mis-matches as some TWTs are
intolerant of a bad VSWR. and could suffer damage. The problem is somewhat
alleviated as all our TWT’s have isolator protector circuits. If in doubt,
there is a selection of microwave pads or attenuators in section 600 if
the situation demands matching. Typically, you may have to insert a 3dB
pad between TWT o/p and load in some applications. Be also aware that when
using TWTs they have to be driven strictly within the
“max drive level” versus frequency chart. These are actually displayed on
the top of each TWT. They also have switch-on/off sequences to protect the
tubes. If you are in doubt, then talk to our staff. We invariably vet the
proposed customer’s capability prior to accepting the hire order to satisfy
ourselves for health & safety reasons. When working at these frequencies
losses can be considerable, so plan your layout to allow for minimum cable
loss from the amplifier o/p. A good selection of microwave cables and adaptors
can be found in section 700.
Finally, do not site an amplifier in the same enclosure where it
is generating an RF field. It is most likely to pick up the field as positive
feedback and run into saturation with damage.