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Spurious Comments


I hope that you all had an enjoyable Christmas break & welcome to the first edition of Spurious for the New Year 2013.
Thanks to all those that contributed to December’s edition of Spurious, you helped to make it a Xmas bumper edition
We have lots to look forward to this year, what with moving venue, Mills on Air day, JOTA,  DX competitions, Foundation & Intermediate license exams we really have a busy year ahead.
In an effort to raise our profile I have started Facebook & Twitter accounts for the club, I hope that all of you Facebook users & Tweeters will

show your support & make your friends, family and anyone interested in amateur radio aware of us. They can be accessed via  Just click on the icons at the top right
Finally I would like to wish you all a very happy and prosperous new year



Michael M6MBM

Silverthorn membership


Don’t Forget: - Subscription to Silverthorn Radio Club is now due. To retain your membership our Treasurer will happily accept the £20 fee

To Measure is to err..
          A Beginners Guide            

Measuring equipment is part of modern life be it the dreaded clock at work, a barometer for the weather, the lux meter for the cricket, the weighing scales used by the other half which either brings about happiness or glumness for a reason I know not. The question is what does the radio amateur really need to know?
The first part is to understand some essential definitions: 

Measuring equipment: All devices used to measure, gauge, test, inspect or otherwise quantify the characteristics of an article.

Precision: A measure of the consistency or reproduction of measurements amongst themselves.

Accuracy: The degree of correctness with which a method of measurement yields the true value of a quantity expressed in terms of an error.

Calibration:  A comparison between a measuring instrument to that of a known higher accuracy.

Standard: An instrument, device or material of known characteristics and of higher precision used to establish and maintain the accuracy of a measuring system or device. 

Clearly by these definitions precision and accuracy are not the same. Just because a dial gives a precise frequency to say six decimal places, it can still be precisely wrong! Calibration is another important factor which unfortunately is ignored by many radio amateurs mainly due to the prohibited cost. The key question, how does the radio amateur know the measurement that they have taken is “correct”?

We can find this out by calibrating the equipment against a known standard. Amateur radio test equipment may indeed be within tolerance when first purchased however once it has bounced  around inside  the boot of a land Rover several times then it’s really only fit for indication purposes. To put this into context some organizations use a CAT system and as can be seen “non-calibrated” is a long way down the list.  

CAT 1: UKAS calibrated.
CAT 2: Calibrated externally.
CAT 3: Calibrated before use.
CAT 4: For indication purposes only (Not    calibrated).
CAT 5: Internally calibrated.

With measuring equipment there are essentially two types of error that may occur:

1. Random errors: This can include: human errors (operating), environmental and stochastic errors.

Parallax: The best analogy I can think of is someone standing to the far left of a clock and stating that is say five past ten when in reality the hands of the clock are actually at ten o’clock.  If you look on some moving coil meter meters there is a small mirror at the back of the scale. If it’s not looked at directly there will be a reflection of the needle not in line.

One character I knew may years ago took some measurements during an experiment at college in the lab. The professor peered over his spectacles as they do (It must take years to perfect that look) at the “results” in a spotlessly clean log book. Suddenly he burst out laughing and promptly handed the lot back

to the poor & now deflated student to be totally redone. Why? Because every single so called “empirical” measurement that he had taken fitted the plot on the graph perfectly, in fact too perfectly!   There were no errors!

Environmental:  This is simply using the measuring equipment in a situation where there is a change in temperature conditions or using the equipment outside its operating temperature specification. Errors may also occur due to electromagnetic interference.

Stochastic: This is essentially a process such as noise which results in random signals.

2. Systematic

Construction errors: These types of errors are due essentially to the construction of the measuring instrument itself.

Approximation errors: These types of errors are essentially due when a linear relationship is assumed.

Ageing errors: These types of errors are due to the ageing of the components within the measuring instrument.

Insertion errors: These types of errors are due to the insertion of the measuring instrument or its probes into the item being measured affecting the actual value.  

One laughable example of a systematic error I can think of is a multi meter at work in which there is always a 0.2 V error. This was “solved” by the engineer using a highly technical calibration process” called “HotBos”

(Hit on Top, Bash on side) Not a recommended process though!    

It may seem obvious but it is important to understand how the measuring equipment that you are using actually works. It’s no good trying to measure a changing waveform if the equipment is using a sampling method internally.  The equipment must be fit for the purpose it is being used for. If a moving coil type is used the internal

impedance of the meter must be such that it will not affect what you are trying to measure.

One area in which people do go horribly wrong is with the use of electronic calculators then followed by measuring. There they go tapping the numbers and coming out with an “answer”. Does the answer actually make sense?  Is the answer of the magnitude that I expected? If the answer on the calculator is obviously wrong then do they go back to the calculating board?

Lets for a moment suppose that you take two different types of measurement in order to put those values into an equation. How does this affect things? Well, unfortunately the errors of each piece of equipment will combine. However the square root of the summation of the errors is a much better approximation.
So we have look at errors in instrumentation

I will leave you with this final thought.
Consider a new naval officer straight out of the academy (before we had gps, sat nav, etc), starched shirt, collar and all that, plotting the precise position of a ship on a chart with the rule and a sharp pencil. Then there is the old sea dog of fifty years plus. When asked the position of his boat he looks at the map and presses his oily thumb print on it!
The question now is who is right!

Leslie G0CIB

Instrument & Measurement Pocket Book
W Bolton II 1996


“I was flying from Sligo to Bute and about half way between Ireland and the Mull of Kintyre, when my engine failed!”


Funny how things happen isn’t it?



Fly-UK had been to Northern Ireland in previous years, but in time for the 2012 adventure the rules for UK microlight pilots flying South of the border had been relaxed.  The crossing is from the Scottish Flight Information Region (FIR) into the Shannon FIR, a straight line which almost follows the border between Northern Ireland and Eire.  These are the huge zones that have control over the airways, of which there are three covering the British Isles.  The third is the London FIR.  So, on a glorious sunny morning, we took the first step - 23 miles across water from the Mull of Galloway to Newtownards, County Down, which seemed to take no time at all.

The route from Scotland to Northern Ireland and into Eire

I was in the company of Colin (Skyranger –CETV) who helps me with the interactive side of the Fly-UK website, John Mundy and Simon Stoodley (Skyranger G-CEZE) aka ‘The Breakfast Boys’ owing to their reluctance to fly before a hearty cooked breakfast, and James Sandars (Quantum G-MKZF) an enthusiastic adventurer who was crossing water for the first time.  I was in my ‘trusty’ Shadow G-MWEZ. 

I bought my microlight in 2004, but even in 2012 I still did not have a radio licence!  Why?  Well, I don’t get much time for flying and even less for sitting exams, so I had put it off - far too long!  Then, at the last minute I heard Wayne Chang was organising a course at Plaistows – my field. So I enrolled and picked up my FRTOL just before the start of Fly-UK. Now I was fully legal! As a part of the exam I had to ask for a bearing from a ground radio station.  That’s used to help position location and is called DF (Direction finding).  I called ‘QDM’ which is the Q code for magnetic bearing from me to the radio station.  I could have called QDR and I would have been given the reciprocal.  The examiner came back with ‘G-MWEZ QDM 280 Class B.’ B means within 5° accuracy.

I also had to deal with an emergency situation – that’s a Mayday or Pan call.  Everyone knows about the Distress call - Mayday – to be used when there is serious or imminent danger, which could include structural or engine failure for example.  Pan calls are less well understood.  They are urgency calls which do not require immediate assistance.  They give the emergency services notice of the possibility of help required.
These calls are made on 121.5MHz – the emergency frequency – and will be picked up anywhere in the country by the Distress and Diversion Cell.  D&D as they are known, monitor the frequency permanently, as do all commercial aircraft, so any pilot can be
sure of assistance wherever they are.

The author folding the chart for the flight into Eire

To fly into Eire we needed to be properly authorised by the Irish Aviation Authority (IAA).  So we had duly sent off photocopies of our documents and the application forms to have our licences validated1.  Now with the Validation documents tucked into our licence wallets alongside our FRTOLs we were ready to boldly go where no microlight had gone before – Shannon FIR – The Final Frontier!
The weather in June was everything from atrocious to diabolical, but with patches of good weather between the storms we persevered and were rewarded with a brilliant trip from Newtownards in NI, visiting Athboy, Abbeyleix, Rathcoole, Bantry, Spanish Point and Sligo.
As we were flying mid-week we didn’t meet many other pilots, but were kindly assisted at airfields with fuel runs.  My memorable location was Rathcoole where we stopped for fuel.  Not because the airfield
owner arranged a fuel run up the road, or the quality of the strip (it had been a wet year), but the service from the garage.

The pump had one of those digital displays; the type with 7 bars that light up to make the shape of each number.  Nothing wrong with that, but the top row of numbers (price per litre) was missing, the second row (number of litres) had some lights but they were not working, and the bottom row, which showed the price had random bars missing in each number.  Now that’s not too difficult if you are serving up to 50 litres, say, but I was filling jerry cans for everyone.  The display was reading something like Ihe:-e my 1:50 mix looked lost.
On top of all that, the pump was £s and Galls, not Euros and litres, but I was assured that it had recently passed a Weights & Measures check!  After a short discussion it was all sorted out, I was asked to pay £120 which was a few pounds less than the true cost and was given a bunch of 9 bananas from the shop for the trip! 
Weird, but appreciated!


After a great visit, the following day we were making our way back to the UK.  A direct flight from Eire to Scotland would save one stage of notifying customs, special branch etc and only 11 miles across water too - just a short hop.  At 3 hours, quite a long flight though.

I was flying from Sligo to Bute, and about half way between Ireland and the Mull of Kintyre, when my engine failed!  Just for the radio practice, you understand, with no risk of wet feet!
OK, I know, flying at 6500 feet I probably wouldn’t

have bothered as I could probably have glided in to Cambeltown on the Mull.  And anyway I was in the company of three other aircraft who would have given the call for me while I prepared for an uncomfortable landing in the water.  What’s more, with a dead battery, when the engine stops my radio doesn’t work!

What the Heck!  I let the others know that I would QSY to 121.5MHz for a Practice Pan.  A little surprised, they followed to listen to my call…
Nothing heard!  After a pause I tried again.
Still nothing heard!
I’d best get the aerial checked before next year.

G-MWEZ Shadow C-D


Over the water I started thinking back to my radio course; recently passed.  All that stuff about requesting a QDM; advising of diversions; Mayday calls…

Yes, and weren’t we supposed to do a Practice Pan at some time to get some experience in. 

My air band radio tuned to the ‘chat’ channel on 123.45MHz for talking to other aircraft
Now, what if I was here, right above the North Channel and I had an engine failure?  Mmmm, why not give it a go and see what response I would get
from those nice boys in D&D.  So here was my imaginary scenario…

           The VFO Projects           

by M6MBM

Week 4 and Peter G4KSE brought in his Heterodyne Frequency Meter, type BC221. The BC-221 is a three tube, heterodyne type frequency meter with an integral crystal calibrator. It can be used to set the frequency of both transmitters and receivers over a frequency range of 125 KHz to 20 MHz the instrument has two ranges - "low" and "high". On the "low" range it operates between 125 and 250 KHz on fundamentals while the "high" range covers 2 to 4 MHz, all other frequencies are determined by using higher order harmonics.

Peter had brought this beastly piece of equipment in to show me how it could be used to calibrate my newly made VFO, however because the frequency meter had not been used for several years there was a procedure which involved having to wind up the voltage on the piece of equipment to prevent the capacitors exploding as they might if you applied full operating voltage to them straight away. As a result another piece of equipment called a Variac was introduced to me on this evening also.
It is worth noting a few very important facts about variacs that will be very useful to users and their safety!

Transformers - The Variac : - Apart from allowing you to increase the voltage slowly, there are many other uses as well. A fully variable power supply is easily made using a Variac and a normal transformer, bridge and filter caps. Any desired voltage is attainable, and it can be varied from zero to the maximum. Using a Variac also lets you test equipment over the full mains voltage range that may be expected in the field, 120V, 230V, etc, it can vary widely, especially in remote areas. Any non-isolated Variac must be considered to be as dangerous as the mains itself, regardless of the output voltage at the time. Because there is always a risk that active and neutral could be reversed, no part of the output of a Variac can be considered safe unless it is stated to be isolated (and tested to verify that this is the case). Since the vast majority of all variacs sold are non-isolated, the output must therefore be considered to be live. For this reason, any Variac should be fitted with an earthed input lead with a normal mains plug. The output must likewise be connected to a mains socket, and all wiring enclosed. On no account should a non-enclosed Variac be used as a bench tool with leads hanging off the terminal block. This is an inherently lethal way to use it, and cannot be discouraged strongly enough. With some variacs, the shaft may not be isolated from the wiper. While unusual, the Carl Zeiss version is an example of a non-isolated shaft. In this case it's perfectly safe, because the secondary is isolated and low voltage. This may not always be the situation though, so before working on a Variac with the knob removed, please ensure that the shaft is isolated from all internal wiring. It's not always easy to see whether insulation is present or not, so a check with a meter is advised. As with all transformers, overloads are permissible, provided their duration is limited and time is allowed for the Variac to cool. If operated at 150% of rated current, a typical Variac can be used for a maximum of about 15 minutes, after which it must be allowed to cool to ambient temperature before the overload is repeated.

We needed to monitor the voltage and current as we wound the voltage up with the Variac, so with the supply off we removed the frequency meters plug top to expose the inside of the plug, then removed the fuse and attached one multimeter across the fuse links, and selected the ac milliamp range to monitor the current in series. The plug was inserted into the variacs output socket and another multimeter connected in parallel across live and neutral to monitor the supply voltage as it was being wound up. Peter G4KSE slowly wound up the voltage over about an hour until we had the full 230v ac flowing through the frequency meter.

Meanwhile while Peter and I were concentrating on this task, Tom M5AJK had been looking at the faulty VFO and its circuitry. To fault find it he had drawn the as fitted circuit down on a bit of paper, and then compared that to the original diagram in the Intermediate book, at which point he noticed an anomaly with the connection across the FET. He had picked up that the gate and source connections were the wrong way round, something which Peter G4KSE and I thought we had checked thoroughly ourselves. The RSGB intermediate course book did have the information but to me it wasn’t very well presented, especially as this was being aimed at people who would have had little experience of building. If you just used the as fitted diagram the book had provided you may have made the same mistake as I had and mirror imaged the FET connections. In my opinion this is where the doubt was raised because the as fitted drawing looked as though you were looking directly down on the FET and the round metal top of it rather than the pins sticking up at you!
The FET circuit diagram was two pages away from the as fitted diagram implying as though it was not needed or not as important. The FET circuit connections were a further two pages away from the as fitted diagram again implying that this was not needed, or important Even though Peter G4KSE and I checked online for the correct connections of the FET and used a circuit symbol and connections identical to the as fitted diagram and drew this down, I still managed to connect the gate and source incorrectly.
Thinking back on it with hindsight if I hadn’t allowed the melting of the capacitor to cloud my judgement maybe I would have looked at the FET sooner. Thinking about it logically, obviously if it hadn’t been connected correctly it would not have been acting as an amplifier circuit, small signal in larger signal out. We had already made sure that there was current flowing through the circuit and this would not have been so if there had been any problems with the components. There just would not have been a circuit there if anything was broken.

I quickly de-soldered

then re-soldered the connections into place making sure to switch them over. I then connected the completed VFO up to Peter G4KSE’s DC variable power supply using some bell wire and wrapping the wires around the battery connectors negative and positive. Now I checked and said it out loud what the connections were on the battery and then applied it to

the battery connector and used the small round connector as the negative and the larger as the positive!
I turned the variable supply on and wound it up slightly then checked the voltage with a multimeter set on volts DC and straight away I noticed that I was getting a negative reading -9vdc. I knew that this was not right! However because I had earlier checked the connections and in my mind had convinced myself that they were correct I couldn’t understand why I was seeing a negative reading suggesting that the connections were reverse polarity. I mentioned this to Peter G4KSE and immediately he spotted what I had done. The smaller connector on the battery connector fits into the larger connector on the battery which was the negative terminal! I switched them over feeling slightly embarrassed for making this beginners mistake, and checked once again with a multimeter this time seeing the correct polarity & voltage. The VFO was now receiving the correct voltage and so therefore now should have been sending out a signal. Using his heterodyne frequency meter

Peter G4KSE started to hunt for the signal from my VFO, it wasn’t long before he homed in on it confirming he had picked up my VFO by placing his hand near the components of my VFO whereby adding capacitive resistance to the circuit and changing the tone of the signal as he moved his hand close to it and then moving it away, repeating this several times so that I could see and hear the tone changing.
Yes it was working! WE were both over the moon.
Next time we will calibrate my VFO using the club Yeasu rig and its VFO to zero beat the upper and lower ranges of the VFO and also build and compare the alternative VFO project.
Michael M6MBM


Editors Note
It should be made clear  that I am a J.I.B Approved Electrician and fully understood the dangers and the care needed for experimenting with mains voltage in the way described. It is therefore not recommended for non qualified personnel to attempt such procedures.



Diary Dates

Club Events This list supersedes all previous ones. Please note these events are subject to change and other events will be added as they are organised.

Friday 21st Dec 2012 – Christmas Party
Wed 26th Dec 2012 – Christmas 2m Net at 11.00am (S20 145.500 QSY S19              145.475 if free or lower channels
Tuesday 1st Jan 2013 – New Year 2m Net at 11.00am

Future events in 2013
Radio Junk Sale                            Jan 2013 –      Date to be determined
Second Hand Sale                        Jan 2013 –      Date to be determined
Thinking Day on the Air     16/17th Feb 2013
National Mills Weekend     11/12th May 2013
VHF National Field day     6/7th    July 2013
Silverthorn Club Camp      Jul 2013         Date to be determined
Jamboree on the Air           19/20th  Oct 2013
Annual General Meeting    25th       Oct 2013 8.00pm.  Probably at New Venue

Local Rallies 2013

Don’t miss these rallies…    Check details with the organiser before making the journey

Canvey Island, Essex.  Vic, G6BHE, 01702 308562 (evenings)


Rainham, Kent.  Trevor, G6YLW, 07717 678 795, trev


Godmanchester, Cambs.  David M0ZEB, 01353 778093,


Foxton, Cambridge.  Lawrence, M0LCM, 01223 711840, rally2013


28 & 29 SEPTEMBER -NATIONAL HAMFEST - RSGB in association with the Lincoln Short Wave Club.
Newark and Notts Show ground, Newark.

12-14 OCTOBER  RSGB CONVENTION – Near Milton Keynes.


If anyone is interested in participating in any special events or contests please make this known at the Friday evening meetings. Why not organise a team. Operation from the TOC is available at most times and Club equipment is available if needed.

Is anyone up for one of the more unusual contests next year? 
If so please contact Tom M5AJK to see if we can get a team together

IRTS 80m Counties Contest 2013
The date for the 2013 IRTS Winter 80m Counties Contest is Tuesday 1st January.


Check the rules at:

Please take note of Rule 4.4 and 4.5 and keep the portion of the band
between 3.650 and 3.700 clear.
Also note the change in Rule 10.1 which states that entries must be received by the Contest Manager not more than 14 days after the contest

Bargains to be had!

Rod recommends …

627 Romford Road
Manor Park E12

Tel:  020 8553 1174

Michael recommends........

JAB Electronic Components for Radio Hams

We normally despatch items twice a week Mondays & Thursdays. We aim to complete all orders as soon as possible and in any case Within 14 days from receipt.

RSGB Special Offers.

From their on-line catalogue

Some of the current special
Offers are web exclusives!

Buy today whilst these offers last!
When they are gone - they are gone!  Or so I’m told!

Only available at

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