## Monday, August 24, 2009

### I passed! - the new sample paper, that is !

Right. There is a new sample paper online at the IRTS website. It is Revision 4, the previous one being Revision 3. Some of the questions are exactly the same, but there are a whole heap of new questions. I sat down and ran through the questions in about 20 minutes. Bear in mind that this is a bad idea, because in the real scenario you will have two hours, and that means time to spot some of the mistakes I made. I got one question on capacitance wrong because I worked it out the wrong way. Tut tut. And there was me telling everyone resistors and inductors are calculated the same way, but capacitors are the opposite.

Tony EI4DIB was here at the time and he reminded me of a handy mnemonic (I think that's what you call it) to remember what to do: think of the first four letters of capacitor - CAPA - and think of it thus:

C - Capacitor
PA - PArallel

So, in parallel, add, and in series, it's C1xC2/C1+C2.

Anyhow, I managed to pass the whole exam, thankfully, so I am greatly encouraged now that my efforts are paying off.

I will try to give you some of the questions I got wrong, in the hope that (a) you don't make the same mistakes and (b) that I can better learn the correct answers.

I should have got this one right, but nevertheless I'll post it here so you can make sure you don't make the same mistake.

4. In the circuit below, ignoring component losses:

A [ ] Current at the resonant frequency and below that frequency will be unaffected
B [ ] Current at the resonant frequency will be impeded
C [ ] Current at the resonant frequency will readily pass through
D [ ] Current at the resonant frequency and above that frequency will be unaffected

The correct answer is B Current at the resonant frequency will be impeded. I answered C incorrectly.

9. A common-base amplifier, using a bipolar junction transistor, can be expected to have:

A [ ] High input impedance and high output impedance
B [ ] High input impedance and low output impedance
C [ ] Low input impedance and high output impedance
D [ ] Low input impedance and low output impedance

Having not done much at all on amplifiers, I simply didn't know the answer to this one. So I guessed. Wrongly. Now don't worry about a question throwing you off like that. I know it's daunting. But there is a margin for error. Remember that, even if you guess, you have a one in four (25%) chance of getting it right. In this case, I was wrong, but not to worry.

The correct answer is C Low input impedance and high output impedance.

13. The sensitivity of a receiver arises from:

A [ ] The bandwidth of the RF preamplifier
B [ ] The stability of the oscillator
C [ ] Its ability to receive weak signals
D [ ] Its ability to reject strong signals

I fell into the trap of thinking this was a trick question. I know that the sensitivity of a receiver is described as its ability to receive weak signals. It was the wording "arises from" that confused me. I needn't have been confused.