RF Amplifiers and Pre-Amps (400's)

Section 400 Content Consideration

This section deals with most types of power amplifiers used within the EMC disciplines. You can browse our range of RF amps and Pre-amps here.

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 is likely to 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.

Pre-Amplifiers

Pre-Amplifiers are sometimes known as signal amplifiers as opposed 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 program. Such files are already entered in our software if you decide to hire a laptop with one of our receivers.

Microwave Power Amplifiers

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. However, we have two pre-amps, items 446 & 447 which can amplify a signal gen output and boost the input to a receiver for shielding work taking the operation up to 40GHz.

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 mismatches 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.