R/O exam papers.

Mimcoman
31st July 2008, 15:12
Does anyone know what happened to all the examination answer papers. If they're still around, it would be really interesting to read what you wrote all that time ago. I had a try finding out a few years ago but got nowhere. (Although I was never actually told that they'd been destroyed, I guess that's the most likely scenario.)

K urgess
31st July 2008, 15:17
Probably went the same way as all the radio logbooks we kept so diligently.
And your MIMCo paybook.
Up in smoke when our history was destroyed in the 80s and 90s. (Cloud)

Ron Stringer
31st July 2008, 16:14
With office space renting at 25-30 per square foot in the early 1990s, (God alone knows what it is now) choices had to be made on how much of the annual budget could be spent on property. Storing mounds of paper that had no possibility of producing any income, came pretty low down the long list of demands on the budget. In a rapidly shrinking market, hard decisions were necessary - do we retain paper records or Radio Officers and Shore Technicians?

Don't be too critical of Marconi, the other radio companies and the GPO/BT examiners - after all the British Government (with far greater resources) chose to dump all except 10% of the merchant ships' log books and crewing records on cost grounds. To retain them would have cost the taxpayer and the MN records had neither strategic nor electioneering) value. The great majority of the population had no awareness of the MN and did not care.

Sad but true.

IanSpiden
31st July 2008, 17:07
I seem to have read somewhere in all these threads that the exam papers were stored in a couple of places for certain years but right at the moment I cannot find it again , one of them was at AMERC

Trevorw
31st July 2008, 18:48
Don't know where the papers are, but I remember vividly 3 questions:-
a. Selector Device, circuit diagram (I could do that in my sleep!)
b. Inductor type alternator.
c. Given L and C, calculate the frequency.

K urgess
31st July 2008, 19:58
I've never forgotten the formula for resonant circuits
fr = 1/2∏√LC
(one over two pie root LC)
The bible (PMG Handbook) has some exam paper examples in the back.

sparkie2182
31st July 2008, 22:59
current gmdss papers are held for (i think) 5 years.....then destroyed.
they are retained for general audit purposes and "spot" checks on marking "tightness".

the question i always recall is that of the "oil filled" capacitor........ given its electrical dimensions..........
calculate its capacitance.

then calculate the capacitance if the oil leaks out............:)


sparkling stuff.

R651400
1st August 2008, 11:10
Give the reason for a BFO in a superhet receiver including circuit diagram.
Gave the simple circuit of a one valve transmitter I tried to build seemed to satisfy the IoW/T examiners.
Ubiquitous AA selector circuit and resonant frequency given L and C values
fr = 1/2∏√LC
or.....

how about this from Harry Watson theory instructor Leith Nautical 1950's...

159200/√LC when values of L and C are microhenries and microfarads

BobClay
1st August 2008, 11:28
Also worth mentioning looking at the dates that these calculations would be carried out without calculators. We were allowed to us slide rules (guessing sticks) at Leith in he 60's, but of course you had to be careful about the decimal point. Failing that, do it the long way, and search out those log tables.
(I work in a school, when I mention log tables, they all stare at me as if I'm from another planet).

mikeg
1st August 2008, 12:50
Thanks Kris for that, I actually remembered that formula for a resonant circuit. Scraping the grey cells more a few come to mind, maybe more later as I dig deeper into the subconcious Xc = 1 over 2pi f c and calculating stage gain mu x RL over RL + Ra. Thinking back most formula were variations of ohms law but devices like op amp theory went into pages..

Mimcoman
1st August 2008, 14:36
I've never forgotten the formula for resonant circuits
fr = 1/2∏√LC
(one over two pie root LC)
The bible (PMG Handbook) has some exam paper examples in the back.
Aye:

"One over two pi root LC equals the resonant frequency".

Also, CIVIL for the way current and voltage interact in a capacitor and an inductor.

etc etc.

You were required to have (in my day) the Lifeguard cct diagram almost off by heart, together with the action of the unit for each dash up to the alarm condition.

Two of the radio questions I vaguely remember were
"Draw the block diagram of an SSB transmitter operating in A3J mode on 4125 kHz, showing the signal path, labelling each block and including the frequencies present between each block",
and
"Describe, with diagrams, the construction of a Bellini-Tosi DF system and how a bearing is resolved".

And there was one asking why the output stage of a vhf fm transmitter could use class c mode...

freddythefrog
1st August 2008, 16:11
I understand that the Liverpool Maritime Museum Library has in its possession
a book or books that name all R/O's who took tickets and also has a section on "EXAMINERS COMMENTS" for each person. OH DEAR! Get the hankies out
guys and stick pins in your eyes.
I personally have not seen this book, too afraid to look in case they made a mistake and they want their tickets back!! Ha-Ha.ftf

King Ratt
1st August 2008, 18:25
Another one from Harry Watson at Leith Nautical College 1960 while instructing in electrostatics.
Quote " Imagine one of my balls suspended from the ceiling" Unquote.
Harry had a set of pith balls which he used to charge up to demonstrate electrostatic attraction/repulsion.

R651400
2nd August 2008, 08:48
Harry almost gave me a fortnight's holidays which was the maximum punishment giving little or no chance of an exam pass. Just as Harry put his head round the morse room door, the large brass cover of Ted Whitehead's favourite morse key used as an ashtray connected with my foot and almost went through the cupboard where the audio oscillator was kept!

"Would you like a fornight's holidays laddie?" was the question rather than the dreaded "Take a fortnight's holidays!"

Trevorw
4th August 2008, 23:30
How about the formula for the dilectric efficiency of a capacitor (condensor):-
akn over 11.3d!!

charles henry
5th August 2008, 17:02
Dont remember whether it was pmg1 or one of the C&G exams, a trick question.

In a resonant circuit with 10 amps and R = 10 ohms calculate the impedance.

de chas

Shipbuilder
5th August 2008, 18:00
Don't know if I am remembering correctly, but didn't ohms law apply at resonance? If so, I suppose impedance was 10 Ohms.
Bob

charles henry
5th August 2008, 18:08
Don't know if I am remembering correctly, but didn't ohms law apply at resonance? If so, I suppose impedance was 10 Ohms.
Bob

Reasoning correct, answer wrong
de chas

BA204259
5th August 2008, 18:14
Mmmmm... at resonance inductive reactance and capacitive reactance cancel each other out, therefore Z = 0. Straining through 50 years for this....Ohms Law applies and current is V/R and not V/Z.

charles henry
5th August 2008, 19:06
Mmmmm... at resonance inductive reactance and capacitive reactance cancel each other out, therefore Z = 0. Straining through 50 years for this....Ohms Law applies and current is V/R and not V/Z.

Go to the top of the class, you are correct +XL=-XC= 0 (at resonance)
I still remember looking at it for a long time thinking it had a catch as it
was too obvious. de chas

Shipbuilder
5th August 2008, 19:08
I suppose that must be the answer with capacitive & inductive cancelling out - overall impedance zero! But glad I didn't make too much of an idiot of myself by at least remembering Ohm's Law applied.

Still remember this from Wray Castle

"In any closed circuit of constant temperature, the ratio of voltage applied to the current set up by that voltage is constant - that constant is the resistance of the circuit." Ohms Law - funny what we remember - didn't really understand it when I learned it - but do now!

Bob

K urgess
5th August 2008, 19:11
I always used to remember that impedance was zero at resonance as one of those little memory things but I'm sure I would have fallen into the trap. (Whaaa)

Shipbuilder
5th August 2008, 19:14
When doing radar in '68, I was fairly happy with all the questions except the last about which I hadn't the faintest idea. With half an hour to go - I scribbled in rapidly deteriorating "frantic looking writing" a single paragraph designed to convey to the examiner that I knew exactly what I was talking about ending with - "run out of time - sorry!" I then sat back & watched the others for the remaining time. Must have worked - I passed!

Bob

sparkie2182
5th August 2008, 21:23
one memory is of a question concerning a combination of Kirchoffs 1st and second laws being attempted by four lecturers...........

we got four different answers.........:)

Kirchoff was never a favourite, as i remember, and being advised to..........

"just redraw the circuit"........never helped much.

:(

BobClay
5th August 2008, 23:04
I was reading these posts when I took a hankering to examine my bookshelves to see if I still had it. Sure enough, a bit dusty now, but there it was, 'Marine Radio Manual' by Danielson and Mayoh.

When I started at Leith in 1967 I had my freshly bought copy under my arm (I'd been told by the college to purchase it). Pretty much a text book for PMG2 and a quite incredible appendix that introduces you to things like the mathematics of complex numbers (amongst other things), and does it in a way that's very understandable.

I've done quite a bit of studying with the OU and I can honestly say this book has a standard as good as their distance learning material. Looks a bit dated now with all those valve circuits though.

andysk
6th August 2008, 10:04
..... a quite incredible appendix that introduces you to things like the mathematics of complex numbers (amongst other things), and does it in a way that's very understandable.

I've done quite a bit of studying with the OU and I can honestly say this book has a standard as good as their distance learning material. Looks a bit dated now with all those valve circuits though.

Hi Bob (Clay) ....

I'd definitely agree with you, an excellent publication. I got mine in 1968 when I started at Norwood Tech, where we had the additional advantage of haveing Danielson and Mayoh as lecturers - very useful !!!!

The best text books from the layman's understandability point of view that I have seen are those needed for prestudy for the OU Mathematics foundation course (M101 in my day !) called Countdown to Mathematics Vols 1 & 2.

Originally about 6 per vol, but I see they are now going for about 5 or 6 times that ! Still the 1981 edition though.

R651400
6th August 2008, 18:56
Go to the top of the class, you are correct +XL=-XC= 0 (at resonance)I still remember looking at it for a long time thinking it had a catch as it was too obvious. de chas
Your original question is nebulous and if what you say is correct then only in series resonance... in parallel resonance impedance is calculated as L/CR ohms...

IanSpiden
6th August 2008, 19:00
I went back to Leith in 1972 to do My 1st Class at the Company's ( P&O) expense which seemed to spur me on a lot more , I guess that I would not have liked to fail having been paid to be there, in any case I was also substantially wealthier than I had been when I was there originally ( I more or less had zero cash) this seemed to make life easier also. The Syllabus seemed to be a revision of the 2nd Class second paper and doing past papers till they came out of your ears , it worked because I passed although I am not sure that I learned any more than I had previously known , now the MED was a totally different story !!!!

BA204259
6th August 2008, 19:16
Your original question is nebulous and if what you say is correct then only in series resonance... in parallel resonance impedance is calculated as L/CR ohms...

I just knew you'd pop up here before long...:) :)

R651400
6th August 2008, 20:02
I just knew you'd pop up here before long...:) :)In senior if not senile years I did a C&G telecomms course.
I don't recommend anyone to even try to prove L/CR is the formula for parallel circuit impedance. It was the exam question forever indelibly stamped on my brain and I'm finally glad to have the chance to prove I have this innocuous piece of information waiting for the opportunity to be set upon the world at large.

BA204259
6th August 2008, 20:11
In senior if not senile years I did a C&G telecomms course.
I don't recommend anyone to even try to prove L/CR is the formula for parallel circuit impedance. It was the exam question forever indelibly stamped on my brain and I'm finally glad to have the chance to prove I have this innocuous piece of information waiting for the opportunity to be set upon the world at large.

And here's me, trying to pretend that I'm a real sparkie, only to discover my shortcomings after all these years...:sweat:(EEK)

R651400
6th August 2008, 20:24
And here's me, trying to pretend that I'm a real sparkie, only to discover my shortcomings after all these years...:sweat:(EEK)
Nah! Nah!
All it does is hurt the head as my old mentor Cliff Taylor would say, have a long draw on his pipe and then continue into the aladdin's cave of radio theory without batting an eyelid....

rusty1946
21st August 2008, 15:06
We were only allowed to use slide rules or log books for our calculations, I preferred the Log tables, I always found slide rules difficult to come up with precise answers

K urgess
21st August 2008, 15:16
While fossicking away through antique radio theroy I came across a reference to "Napierian Logarithms".
That was when my head really began to hurt. (Whaaa)

Hated slide rules. Far too much of an "analogue" device. (?HUH)

Mimcoman
22nd August 2008, 00:37
Log tables were great - once you'd cracked the code. I still have one somewhere. Never took to slide rules.
The first calculator I saw was a kit-built Sinclair item, built by a Mimco tech in Liverpool (Stan something?), early 1970s. It could +, -, x and ./., used leds for the dispay and cost about 50, I think.

R651400
22nd August 2008, 07:48
John Napier, Scottish mathematician still proudly remembered through Napier College Edinburgh.
Inventor of base 10 logarithms Napier worked out if 10 to the power 2 was 100 there must be lesser numbers for 10 to 1.3 (19.953) and 10 to .6 (3.981).
Adding the two together gave 10 to 1.9 (79.433).
Using Napier's log tables made maths a lot easier than trying to multiply the two real numbers.....

NoMoss
22nd August 2008, 08:05
Nah! Nah!
All it does is hurt the head as my old mentor Cliff Taylor would say, have a long draw on his pipe and then continue into the aladdin's cave of radio theory without batting an eyelid....

Was that who we used to call 'Abdul'? If so it was he that finally explained Algebra to me and simultanious (?) equations - a real Eureka moment.

trotterdotpom
22nd August 2008, 11:31
"While fossicking away through antique radio theroy I came across a reference to "Napierian Logarithms"."

See those Kiwis are not only good for sheep shearing.

John T.

R651400
24th August 2008, 10:35
Came across what must be one of the first post war second class exam papers.
Marked with an asterisk making it a compulsory question.
Try this one.... Log tables, slide rules and calculator permissible...

What capacitance is necessary to tune a circuit containing an inductance of 25 microhenries to a wavelength of 3770 metres. What is the frequency in kilocycles?

Baulkham Hills
24th August 2008, 14:15
In 1967 I passed the theory part of the 2nd class and was repeating the
practical and morse. I did the theory part of the 1st Class, because I would most likely pass the 2nd class practical without much difficulty.
The first question which was compulsary was about 1/2 convergency error on D/F bearings and explain the formula. It was all downhill after that.
I used to test 2nd mates with the question occasionally and very rarely did I get the correct result, its basically a navigational question about allowing for the lines of longitude in long distance bearings.
Needless to say I did not make it but I did get the 2nd class. A few years later it all changed to General cert but I never bothered to change to that
as I felt it did not make any difference to getting a job.
Now 41 years later I am still at sea as an E.T.O. and the sparky is dimming in memory. Recently I had an E.T.O. cadet and I asked him
to repeat ohms law and he said he had heard of it but forgotten it.
This was after 2 years in College. So maybe I was not so bad after all.

BA204259
24th August 2008, 16:58
What capacitance is necessary to tune a circuit containing an inductance of 25 microhenries to a wavelength of 3770 metres. What is the frequency in kilocycles?

Wish I had a quid for every year since I last did this.

How about f = 79.57 kc/s

Capacitance required = 160 millifarads

R651400
24th August 2008, 18:03
Wish I had a quid for every year since I last did this.
How about f = 79.57 kc/s.. Capacitance required = 160 millifarads

You and me both BA204259!
The 79.57 kc/s was the easy part. I'm still working on the capacitance.
More to the point, without the help of logs this question would have taken up the entire exam time to work out the answer!

BA204259
24th August 2008, 18:46
You and me both BA204259!

More to the point, without the help of logs this question would have taken up the entire exam time to work out the answer!


Last time I did this I was using log tables. Don't have any now and not sure I'd know how to use them anymore, so used a calculator. I'm sure I would have been happier using logs though, less chance of being a decimal point out.

R651400
25th August 2008, 06:45
How about f = 79.57 kc/s
Capacitance required = 160 millifarads

Using Harry Watson Leith Nautical theory instructor's easy method:-

f= 159200/√LC when L and C are in microhenries and microfarads.

I concur c = .16 ufd

BA204259
25th August 2008, 09:05
Knew I'd be out a decimal point (or two). Using your shortcut formula it does work out at 0.16 microfarads. Have tried to work it back using the f = 1/ 2 pi root LC but can't as my calculator throws a sulk if I ask it for square root of 0.00000000004. Need either logs or a power/scientific calculator which I haven't got. Still, it passed an hour on a dull, cloudy Sunday afternoon.

BobClay
25th August 2008, 10:38
If you're running windows, the inbuilt calculator (set to View/Scientific) will easily handle that.

R651400
25th August 2008, 11:21
Knew I'd be out a decimal point (or two). Using your shortcut formula it does work out at 0.16 microfarads. Have tried to work it back using the f = 1/ 2 pi root LC but can't as my calculator throws a sulk if I ask it for square root of 0.00000000004. Need either logs or a power/scientific calculator which I haven't got. Still, it passed an hour on a dull, cloudy Sunday afternoon.

BA204259..The concur bit was acceptance of your answer excepting millifarads thru me ie 160 millifarads = .16 microfarads, both answers hopefully the right one or we'll appear to be a right pair of duffers!

trotterdotpom
25th August 2008, 11:42
I googled up a site which gives you the frequency for any wavelength in metres and another which gives you the capacitance or inductance for any resonant frequency. Looks like you're both right.

Personally, I always preferred logs to a slide rule. Slide rules were good for drawing straight lines with, but there was something sexy and reckless about the logarythm method.

John T.

BA204259
25th August 2008, 12:16
ie 160 millifarads = .16 microfarads, both answers hopefully the right one or we'll appear to be a right pair of duffers!

Sadly, we are a right pair of duffers. 160 millifarads bear as much resemblance to 0.16 microfarads as I do to Mme Cecilia Sarkozy.

Reduce it to the most basic, to wit, Farads.

My 160 millifarads = 0.16 Farads

Your 0.16 microfarads = 0.00000016 Farads

You see the dilemma here? Not a lot of resemblance(Smoke) It all goes to prove that what was dead easy as a 17 year old is not so 50 years on. (Just in passing, my brain is not the only bit of me that doesn't work as well as it did 50 years ago.(EEK) ).

Mimcoman
25th August 2008, 12:16
BA204259..The concur bit was acceptance of your answer excepting millifarads thru me ie 160 millifarads = .16 microfarads, both answers hopefully the right one or we'll appear to be a right pair of duffers!
I hesitate to enter this as, although I got 0.16uF, I spent a hour trying to work out where I'd gone wrong! Never have had confidence in my maths skills, or rather my lack of maths skills .

But shouldn't 160mF be the same as 160000uF? If you split a number into smaller sections, then the new total should be higher?

(Gulp)

Mimcoman
25th August 2008, 12:20
Sadly, we are a right pair of duffers. 160 millifarads bear as much resemblance to 0.16 microfarads as I do to Mme Cecilia Sarkozy.

Reduce it to the most basic, to wit, Farads.

My 160 millifarads = 0.16 Farads

Your 0.16 microfarads = 0.00000016 Farads

You see the dilemma here? Not a lot of resemblance(Smoke) It all goes to prove that what was dead easy as a 17 year old is not so 50 years on. (Just in passing, my brain is not the only bit of me that doesn't work as well as it did 50 years ago.(EEK) ).
OK - as we posted at the same time, I'll withdraw my entry in deference to BA204259's explanation.

(heaves sigh of relief)

BA204259
25th August 2008, 12:35
But shouldn't 160mF be the same as 160000uF?

(Gulp)


Well spotted Mimcoman, spot on. Nice to know that not all we ex-R/Os are complete duffers.

Now that's sorted, Im still not sure of the correct answer because I can't work it out, so am very happy to defer to R651400 and you with your answer of 0.16 microfarads..:) :)

Correction: I am sure that you and R651400 came up with the right answer.

R651400
25th August 2008, 12:51
BA204259 and Mimcoman, I see my maths is going the same way as my golf!
Duff, duff and more duff..My milli to micro or vice versa was a definite duck hook of the tee. Fore!!!!!!...

Can I rest on my laurels that the answer is 0.16ufd or has anyone a different answer?

BA204259
25th August 2008, 13:07
If you're running windows, the inbuilt calculator (set to View/Scientific) will easily handle that.

Bob, my head hangs in shame. After all this time I never knew that. At least I do now..(Thumb)

Mimcoman
26th August 2008, 18:54
This is the 1st class Radiocom paper I sat in 1971, which I found while burrowing through my loft on the hunt for another document. There's another question on the other side, dealing with the calculation of capacitor time constants, charge and energy dissipation, and the curves for current and voltage changes while charging and discharging.

After the practical part, I remember being told by the examiner that this was the last full 1st class paper and that future 1st class exams would be for upgrades and resits only. Judging by comments elsewhere on the forum, though, I guess this was not the case.

The first MRGC exam took place at the same time.

(Excuse the scribbles - I didn't know the paper would be up for future display at the time.)

K urgess
26th August 2008, 18:58
Glad I don't have to do this anymore. [=P]

Mimcoman
26th August 2008, 18:59
You're not packing in the forum, are you?

DON'T DO IT!

(Or have I misinterpreted....)

K urgess
26th August 2008, 19:02
You should be so lucky. [=P]
I meant the theory, Mimcoman. (EEK)
If I ever need it again, which I doubt very much, then I can just ask you lot.
Whether I'd get the right answer or not is debatable. (Jester)

Mimcoman
26th August 2008, 19:23
I'm with another person who posted earlier in this thread (Hi, Spatz). Most of the theory wasn't used at sea - not by me, anyway - and the so-called maths wasn't really maths at all, just memorising formulae and their manipulation. It was the manufacturer's courses which I found useful - and which got me extra salary with Thos and Jas on their bulkers and containerships.

R651400
27th August 2008, 06:20
The only two compulsory questions in the 2nd Class exam paper I mentioned both involve maths.
GTZM-S your starter for ten....
Two wires of equal length have sectional areas 0.12 sq inches and 0.15 sq inches respectively. If the resistance of the smaller wire is 10 ohms what is the resistance of the larger wire.

.

BA204259
27th August 2008, 08:23
While GTZM-S is waking up I'll chuck in this quick answer, just for starters.

8 ohms.

R651400
27th August 2008, 10:27
BA204259... Beating GTZM-S to the buzzer and if it is the incorrect answer, Bamber Gascoigne says you lose five points.

BobClay
27th August 2008, 10:47
I'm not going to be picky here lads ... (cough cough), but the 8 ohm answer is only correct if the two wires are made of the same material, which looking at that question, you have to assume.

I would have to add that having a downer on maths is and has been very common which I think is fairly sad in a country once noted for it's science and engineering. For example, for me, alternating current theory only ever made any sense mathematically because positive or negative reactances don't mean much unless you approach them from a mathematical point of view.

But .... since I work in a school these days .... I see math is still being regarded as some sort of black art.

K urgess
27th August 2008, 11:43
My initial response is, "Who cares!" [=P]
My secondary response is "Where did I put that Avo!" (?HUH)
My third response would be that the 8Ω sounds about right since the resistance per square inch is probably 1.2Ω. (Whaaa)
Which would bring me back to my first response.(Sad)

Baulkham Hills
5th September 2008, 13:48
Hi there

This question might be of some curiosity value,
it was a compulsary question on Technical Electricity paper from 1968 2nd Class PMG

In an a.c circuit comprising Inductance, Capacitance and Resistance in series.
the ratio of inductance to capacitance (L/C), at the resonant frequency is 10,000.
Given that the resistance of the circuit is 5 ohms,
calculate the following :-
(a) the Q-factor of the circuit.

If an A.C. voltage of 100 volts (r.m.s.) at the resonant frequency is applied across the circuit, determine:-
(I) the value of the supply current :
(ii) the r.m.s. voltage across the inductance.

Cheers

K urgess
5th September 2008, 13:49
I feel a headache coming on!
Where did I leave the key to my darkened room. [=P]

charles henry
5th September 2008, 14:36
Looking at the resonance type questions, would anyone like to buy an
old GR type 916-A radio frequency bridge in as new condition. Weighs a ton but works like a hot damn and gives you accurate XL and XC measurments
up to 30 mhz. Paid $400 for it many years ago, no longer use it (Cant lift it).
(Will throw in a marconi signal generator that uses those glass things)

Please note that for an aincient type I have kept up with all the recent technoligy ie I use Mhz instead of the more descriptive but old Megs or mc/s
de chas(Pint)

K urgess
5th September 2008, 14:44
Sacrilege, Chas. Who was this Herz feller anyway. Something to do with car hire, eh! [=P]

Good offer but the delivery costs from Canada to Yorkshire precludes my participation.

Cheers
Kris

charles henry
5th September 2008, 17:50
Sacrilege, Chas. Who was this Herz feller anyway. Something to do with car hire, eh! [=P]

Cheers
Kris


I hertz that he was the bloke who discovered "non-ocean" waves

(This is not true pun- ishment)
de chas(Pint)

R651400
8th September 2008, 12:15
In an a.c circuit comprising Inductance, Capacitance and Resistance in series.
the ratio of inductance to capacitance (L/C), at the resonant frequency is 10,000.
Given that the resistance of the circuit is 5 ohms,
calculate the following :-
(a) the Q-factor of the circuit.

If an A.C. voltage of 100 volts (r.m.s.) at the resonant frequency is applied across the circuit, determine:-
(I) the value of the supply current :
(ii) the r.m.s. voltage across the inductance.


Q factor 20 (Q = 1/R √ L/C)
Series resonant circuit, capacitive and inductive reactance are equal and cancel each other out
Supply current 20 amps (V/R)
RMS voltage across inductance 0.

Now where did I put my car keys??

jaydeeare
8th September 2008, 12:28
Kris: Sacrilege, Chas. Who was this Herz feller anyway. Something to do with car hire, eh!

Why did the MegaHertz?

Because the Kilobytes!

BobClay
8th September 2008, 15:39
Not sure you can say the rms voltage across the inductance is 0 volts. No DC voltage drop will be generated admittedly (separating the resistance of the coil out). If you have an ac current passing through a reactance it must generate a voltage. The overall circuit reactive voltage will cancel out, but I'd have thought you'd have a reactive voltage of 2000 across the inductance. A similar antiphase voltage across the capacitance.

This is a nasty question because these sorts of currents and voltages would put anybody off such answers..

R651400
8th September 2008, 18:17
I thought my answer would be to simplistic for IoW/T examiners and BobClay's answer looks more the ticket.
There is a resonant rise of voltage over both L and C equal to voltage times Q factor ie 2000V. Question is it peak to peak or rms?
Nasty indeed as this would certainly have been a compulsory question with each answer dependent on another.
Any one wrong, maybe goodbye ticket.

BobClay
8th September 2008, 19:09
It's a sign of the times that my current work in electronics (which is about 100 percent computers) makes me regard such voltages and currents (like kilovolts and tens of amps) as some sort of 'witchcraft'.

I guess it's been a long time since I meddled with radio/radar transmitters.

Still at least you don't end up with three adam's apples (two of em having moved up from about 3 feet below) when you get zapped by solid state voltages.:D

IanSpiden
12th September 2008, 18:36
I agree Bob , having sailed as "Communications Officer" which was the bumped up name from "Chief Radio Officer " which was the starting rank with HAL in 1996 , I dont know what you were chief off as there was only 1 and never even dealt with a radio as they only has satellite comms , in any case it gave the company an excuse to give us the telephone exchange to look after , unless you are totally stupid the worst zap you can get is 50 volts however I have had a few hilarious moments from people when you tell them to " hold those wires for a second " when you are wiring up new phones.
They then gave us another rank which was IT officer which was the same job but only even more computers and gave the telephone exchange back to the Electricians who were also looking after the Radars , strange how things worked out !!

BobClay
12th September 2008, 20:16
which was the starting rank with HAL

You worked with HAL ?

I heard those HAL 9000's could be a bit unpredictable, especially if your name was Dave ....


"Just what do you think you are doing ? ........ Dave ?"

(Jester)

Mimcoman
14th September 2008, 00:34
You worked with HAL ?

I heard those HAL 9000's could be a bit unpredictable, especially if your name was Dave ....


"Just what do you think you are doing ? ........ Dave ?"

(Jester)

And the gyro-stabilisation of the dish antenna (sorry - somehow aerial doesn't fit here) could also be a bit dicey...

IanSpiden
14th September 2008, 14:36
And they are full of stars as well !!! I wish the dam computers on the ship could have talked they might have told the idiots using them what they were doing wrong .

R651400
14th September 2008, 15:05
Are we talking HAL Comms Corp Urbana Illinois? Inventors of Clover? The only HF single frequency duplex digital mode ever.
I bought the P38 amateur radio version modem some ten years ago and there is nothing to date can give the same standard of performance.

Mimcoman
14th September 2008, 18:58
Sir Arthur C. Clarke; 2001: a Space Odyssey; the HAL 9000 computer on the Discovery; HAL = IBM back one letter.

BobClay
14th September 2008, 22:36
Strangely Arthur C. Clarke said the one letter difference from IBM was purely co-incidental. He stated that HAL stood for Heuristic Algorithm.

He might have had his tongue in his cheek when he said that though.....


I remember the P38. Made be Walther before WW2 it was one of the first double action semi-automatic handguns and found further fame in modified form as the 'Man from UNCLE' gun.

(and I suspect there's a few here who remember 'The Man from UNCLE').

(*)) (Gleam)

R651400
15th September 2008, 02:40
Haven't really established if we are talking about the same HAL.
Interesting theory on the Man from UNCLE but I'm more inclined to think the P38 clover modem was called after the Lockheed P38 Lightning WWII fighter plane.

Mimcoman
15th September 2008, 02:40
I remember the P38 as well - the American twin-engined fighter which famously intercepted Admiral Yamamoto's flight over the Pacific in 1943.

Mimcoman
15th September 2008, 02:41
de Mimcoman = snap +va

mikeg
15th September 2008, 10:11
I remember the P38 as well - the American twin-engined fighter which famously intercepted Admiral Yamamoto's flight over the Pacific in 1943.

Far too many coincidences this morning - I was born in 1943 and will be flying a PA38 later today (but not over the Pacific) ..spooky eh? (K)

R651400
15th September 2008, 12:00
Known to the opposition as der gabelschwanz teufel or the twin tailed devil, unlike the Hurrican or Spitfire, I don't think the P38 Lightning or any other fighter plane the US produced would have survived against the Messerschmitt bf ME 109, Focke Wolfe 190 or Japanese Zero in the early stages of the war.
Not until the P51 Mustang built by Northrop to a British design did the US eventually come up with one of the the best fighter planes of WWII.

Ron Stringer
15th September 2008, 16:59
If these are answers to PMG questions, I can only be glad that I didn't take those papers. Had enough trouble with Fleming and Bellini-Tosi without getting involved with Messerschmitt and Focke-Wolf.

IanSpiden
15th September 2008, 18:49
The HAL I am talking about is

Holland America Line but I enjoyed the Arthur C Clarke banter I actually thought the 2010 book and film were better than the originals

Shipbuilder
15th September 2008, 19:24
Long long ago in early 1962, standing outside the "gear room" at Wray Castle, awaiting the orals for 1st Class, I remember thinking "I am absolutely sick of all this, if I pass this exam, that is me finished with studying!" I did pass (although I shouldn't, because at that time I was simply not capable of sending morse at more than 21 wpm). The examiner did stop me after about 30 seconds and reminded me it was 25 I was supposed to be sending at. He then suggested I made a desparate effort in order to attain the required speed. I complied and after about five seconds, he shouted "stop, OK!" Much to my surprise, I passed. Years later, he did a radio survey onboard SAGAMORE & I thanked him for his kindness. He just waved it aside & said it was OK, he knew I would make the grade. What a splendid fellow! How I hated exams. Only passed the radar because B & C said it was back to cargo ships if I failed. But the MED was certainly well beyond my humble capabilities, so I walked out half-way thorugh (good decision as it turned out) Fought & raged against exams & advancing technology until finally getting fed up & quit in late 1992, by which time I was living & coping with satcoms, bloody transistors, e-mails, fax machines, teleprinters, videos, computers, satcoms, solid state, integrated circuits etc ad infinitum. Can still design & build a valved superhet though - the rest you can keep. Tomorrow, I am following up a lead to purchase a few hundred more of my beloved valves.
Bob

Mimcoman
16th September 2008, 19:43
Re PMG examiners. I sat for a Special certificate in 1966 - examiner was Mr R Hill. My 2nd class in 1969 was Mr R Hill. 1st class MPT examiner was someone else. When I joined the GPO coast radio stations in 1979, I was taken for the station walkabout (when an IoWT went over the station with you for a couple of hours to see if you had managed to come up to the required station equipment knowledge to be made permanent staff) by - you've guessed it - Mr R Hill. He was good enough to mention that he remembered me from the past; at the time, I wasn't sure if that was good or bad.

I guess, given the closed world of the UK/Irish/Commonwealth Radio Officer fraternity (and sorority, to be pc), this wasn't too uncommon, but I haven't heard of anyone else who met up with the same examiner a few times. Anyone else?

Bill.