Wednesday, 31 August 2011

Requiescat in Pace

Saddened to hear news of the death of Anthony Edgar "Tony" Sale, whose work on the rebuild of Colossus was central to the preservation of Bletchley Park and the establishment of The National Museum of Computing.


Tony was there tending his creation when I visited Colossus last year - he leaves a legacy not only in the physical rebuild of the machine, but also in the enthusiasm he fostered in a team of colleagues who helped with the rebuild and now ensure the preservation of some important pieces of history.

...-.- de m0xpd

Sunday, 28 August 2011

A Splendid Jaunt

Just back from a few days in the beautiful surroundings of Pickering, North Yorkshire, where we stayed in a delightful cottage conveniently positioned mid-way between a trout lake and a railway station - the very 'gate of heaven'!


Whatever Kirstie and Phil might bang on about, this establishment didn't just rest on its location laurels - it was beautifully presented as well. In addition to the little two-bedded cottage in which we stayed,"The Limes", the good folks at High Mill also have a larger property for rent, which sleeps up to 12.
The view from my armchair was fantastic - here's 7F 0-8-0 heavy duty freight locomotive 49395 working a passenger service tender-first back to Grosmont...


We took the same trip ourselves a few days later, travelling back from Grosmont in fine style in the first class observation saloon at the end of a nice rake of wooden LNER coaches (you can see the new Barbour Beaufort I got from the Orvis store on Pickering's Market Place hanging over the back of my armchair)...


The staff at the Orvis store deserve special mention as they honoured the "£20 off" voucher that came with our railway ticket, even though I'd purchased the coat two days before!

Things took a turn for the better when some thoughtful chap came and offered us drinks - here's my "Gin and Tender"...


(the tender being that of the 9F engine 92214 "Cock O' The North", which strained and sighed on the other side of the glass whilst pulling us back to Pickering).

Here's the observation saloon from the outside on reaching the shelter of Pickering Station's new roof...


Aside from many other notable delights (Gannets at Bempton, the Castle atop the hill behind High Mill and a sublime piece of rib-eye steak at The White Swan), the trout lake served up its usual entertainment...


I think it is actually bigger than the one caught in April - certainly your humble servant looks pretty pleased with himself...


If you want a break in a great location, give High Mill a try - seen here photographed from the observation saloon...


I certainly will be going back.

The only fly in the soup was the trouble I had getting any signal out (2W on 40m CW from the FT817 and Whip). Still, the Mill is on a road called the "Undercliffe" - the clue's in the name!

...-.- de m0xpd

Saturday, 20 August 2011

Heavy Artillery

The same sale of surplus gear that bumped up my BNC socket stocks also saw me bid a tenner to win a wideband RF power amplifier, which runs 12 Watts, 200 kHz - 32 MHz, made by RF Power Labs, Inc. of Kirkland, WA. It had Albert, G3ZHE's sticker on it, so I knew it had come from a good home. Albert told be that previously it had been in Jim G3NFB's shack - it is nice to be keeping it in the Warrington family!

Today, I had chance to power it up and see what it does...

I hooked it up between the output of my multi-mode beacon (Blogs passim), which happened to be set to the 30m band, and the G5RV. Here is the "brick" on the bench...


You can just see one of my switched attenuators atop the amplifier, throwing away some of the input (the amplifier needs 1 Volt in for full rated output).

I was immediately spotted on WSPR in the USA by Edmund, WB1FIG, in Plainville, Massachusetts...

having previously only been heard in Europe.

I do get into the US on occasion with the standard 50mW on 30m, as demonstrated last night, when Douglas, W3HH, heard me once again in Florida...

Having fired WSPR signals over the pond with my new "big gun", I had a look to see if my other modes were being heard further afield. Sure enough, I could just make out my FSK-CW and Hell signals on Bill, W4HBK's grabber in Florida (although you do need to know where to look)...


Of course, the QRSS modes into Europe were loud and clear, as seen on Joachim, PA1GSJ's grabber...


In fact, Joachim was also reporting spotting my WSPR signals both during and after the 5 Watt QRO test. Switching from 5W back to 50mW is a x100 change in power (-20dB) and, sure enough, Joachim's reports showed pretty much a -20dB degradation in SNR between two adjacent spots...


So - the bench RF amplifier works a treat.

Apologies to anybody offended by the fact that I couldn't be bothered to change reported power in my WSPR message during the short test - it is a chore re-programming the PIC - mea culpa!

...-.- de m0xpd

Sunday, 14 August 2011

Italian Job in Toytown

The XYL's father is something of a model railway enthusiast - the photo below reveals the ironic understatement...


During our last visit (in which I took the photo), he asked me to make a traffic light controller - no doubt in an attempt to bring order to the anarchic road-rage one otherwise meets at a 1:76 scale crossroads.

Of course, a traffic light controller is a pretty trivial problem in Finite State Machines 101, so I quickly whipped up a system based on a PIC16F676, with on-board LEDs to monitor progress and open collector outputs to switch on and off the "grain-of-wheat" bulbs which the Toytown traffic engineers have used.

Here's the system under prototyping, connected to my PICKit2...

and here's the translation to a PCB...


All pretty dull. So I decided to fool around a little...

Readers will remember the havoc that can be wrought by messing with traffic lights, as demonstrated in the movie classic "The Italian Job".


I decided it would be fun to introduce an occasional state of confusion in the traffic signals on my father-in-law's railroad - so I programmed in a display which would look good on the Golden Mile...


video

(Interesting how the video - captured by my iPhone in low light conditions - is incapable of resolving the colour of the bright monitor LEDs)

The traffic light chaos only kicks off every 200 complete cycles, so you have to be watching the lights (or driving past at just the wrong moment in a 1:76 scale car) to see it.

Let's see if he notices!

...-.- de m0xpd

Monday, 8 August 2011

Appreciation as Grabber Goes QRT

A few days ago on the KnightsQRSS Mail List Johan, on5ex, announced that his excellent QRSS grabber is soon going QRT.

Johan and his grabber have been giving wonderful service to me and to many QRSS operators for many years. In fact, it was Bill Meara's talk of this mysterious station up in Belgium picking up signals from The Eternal City which started my interest in QRSS.

Johan became the second station to report seeing my own QRSS signals and has been picking me up ever since (including back in the day when my Hellschreiber was UPSIDE DOWN!!).

So - now its time to say a huge THANK YOU to Johan and to wish him every success in his new games with other radio modes.

73 dr OM Johan,

...-.- de m0xpd

Enigmatic déjà vu

I was lucky enough to find myself once again in striking distance of Bletchley Park yesterday and enjoyed another interesting visit. Just like last time, the Battle of Britain Memorial Flight treated us to a fly-past - this time by a Spitfire...


Having last time focussed much attention on Colossus, I was determined to spend a little more time looking at the Bombe (which itself has been the subject of a re-build project) ...


I was fortunate to be able to chat with one of the guides, who explained in considerable detail the operation of this impressive machine. I don't know her name or her background, but she certainly understood operation of the Bombe in depth and I am grateful for her expertise.

Talking about expertise, I was pleased to chat once again with David Wright, g3zpa, who gave me some more information about the original (long-wire) antenna systems supplied for use with the Paraset.

In addition to the aircraft flypast, there was an impressive gathering of classic cars with the inevitable superabundance of MGs (I'm allowed to say that as an MGB owner)...


However, other marques were well represented too. The car of the show (for me at least) was a drop-dead-gorgeous Alfa Giulia Veloce - but I was pleased to see some nice 3-wheeler Morgans...


These 3-wheelers are of interest partly because the XYL's grandfather used to own one and partly due to their pivotal role in the plot of Dorothy Leigh Sayers' "Have His Carcase". Morgans more generally have a place in my heart as the XYL and I went on honeymoon in a 4-4. Happy days!

Cars and aeroplanes aside, there was lots more to interest me at BP - not least in my first visit to The National Museum of Computing which, appropriately, is in the same building as Colossus. After seeing the PDP8's of my youth I was pleased to see a healthy display of analog computers (which - for those of you who don't know - solve differential equations by electrical ANALOGY) amongst which was something I'd never seen before: a hybrid analog AND digital computer...


In truth, it was an analog computer with a few digital elements (flip-flops etc) along the bottom "row" in the photo above.

I was also delighted to find an example of the main board from a Tangerine "microTan 65"...


One of my first computers was built around this 6502-based system marketed as a kit by Tangerine. There was a basic interpreter, a disk operating system and all sorts of goodies. Nice to see it again!

However, the high spot of my visit to the National Museum of Computing was certainly the Domesday systems, based on BBC / Acorn hardware and in the news recently because of the "Domesday reloaded" initiative. Here's one of the two working systems at BP...


We were staying with the in-laws, near Pulloxhill, Beds., so we used the amazingly modern multi-media interface to search for Pulloxhill and pulled up a picture of the characteristic water tower...


Here's a link to the photo on the web-based Domesday Reloaded resource.

Partly (I am told) in consequence of the recent financial debacle at the RSGB, the new radio centre isn't yet open to visitors...


... but we did call into the MKARS club house (in an old generator building on the BP "campus") where I had a nice chat with Graham, a G7 licensee (I missed the rest of his call), before driving back to Pulloxhill.

On the drive back we stopped to take an up-to-date shot of the water tower...


Sitting outside drinking a cup of tea half an hour later, the day was crowned by an unexpected flypast of a Consolidated Catalina, the conspicuous lines of which were unmistakable even at altitude...


I assume she was G-PBYA, which is "berthed" at Duxford - she certainly was heading in the right direction!

Perfect end to a(nother) grand day out!

...-.- de m0xpd

Saturday, 6 August 2011

Harvesting Parts and Knowledge

My attendance at weekly meetings of my radio club has been rather patchy of late (pressures of work intruding on the finer things in life), but my last visit coincided with a Sale of Surplus Equipment, at which we managed to capture some of the excitement of the last few minutes of Bargain Hunt (albeit with more desirable items for sale, naturally). In addition to a nice Linear Amplifier (which allows me to make vulgar QRO emissions at 12 Watts, should I ever want to get involved in EME or similar games Hi HI) I was winning bidder on an old piece of kit which bristled with silver plated BNC sockets - 19 in number...


Perhaps you can make out the label - "Junk but spare sockets". A 50 pence bid secured the item.

A side panel carried identifying marks, revealing the object to be from the Hewlett Packard stable...


but some searching on the 'net hasn't provided any more information on pedigree, use, date or other aspects of provenance.

Taking off the sides revealed a set of 11 parallel "channels" (ten of which are connected to BNC sockets on the "front" and the last of which leads to a socket mysteriously located off on one side)...


Casual inspection suggests the unit is some kind of switching/multiplexing device (the clue was in the name on the side of the box!!) with a number of input signals multiplexed onto a number of output channels, using diode switching. The channel select and other control signals apparently were applied through the Centronics-style connectors seen at the right-hand end of the photo above. The whole thing was beautifully built - seemed a pity to pull it to pieces - but here's one channel stripped out of the enclosure...


At this point I had completed the harvest of BNC sockets - now I was about to harvest a different resource.

You can see a line of devices in glass envelopes protruding from the bottom of the board in the photo above. Unsoldering one confirmed my initial identification as a diode and a quick test with the multimeter showed a forward voltage drop which suggested the diode to be of the Germanium persuasion.

I couldn't see any identifying marks, but the glass envelope was clearly marked with colour rings - as on a resistor...



I figured the colours were brown - white (or, possibly, grey) - green (with a rather indistinct black blob at the other end). I had never seen colour coding on a diode before - so off I went to the internet to search for an explanation.

I learned two important nuggets of information, completely new to me...

Firstly, colour codes - exactly those familiar to us from resistors - were indeed used on diodes and semiconductors in general. That made these diodes "195"s - but that didn't make much sense. Until I recognized a second fact which had been staring me in the face for decades; semiconductors were often named using a system in which the device type (i.e. diode) was followed by a numerical name. The device type was signified by the Number of junctions ("N" for number).

According to this scheme a "1N" device is a diode (there being one P-N junction defining a diode), as in the entirely familiar 1N4148. Similarly, a "2N" device is a transistor (there being two P-N junctions in a [BIpolar Junction] Transistor), as in the entirely familiar 2N3904. It is so entirely obvious when you think about it that I'm surprised I'd never realized before!

I am used to learning something about the nature of a valve/tube from its (alpha-numeric) name - as in an ECC83 being a double triode and a PCL86 being a triode-pentode, the E and the P signifying different heater requirements. However, despite a lifetime of using diodes called 1Nxxxx and transistors called 2Nxxxx, it simply never occurred to me to notice the significance of "1N" and "2N".

So - as well as a rich harvest of BNC sockets, I also had harvested some knowledge. Unfortunately, I'm still not yet out of the woods, because I don't yet know how to put all the pieces of the jigsaw together...

Does the "195" on my diodes mean they are 1N95s? Sure enough, there is a Ge diode called the 1N95. However, my internet researches suggest that the "1N" identification of a diode wasn't included in the colour coding scheme, suggesting that the diodes are 1N195s. The 1N195 seems to be a Si device, which isn't consistent with the 0.23V forward Voltage drop I measured.

If anybody can explain this, I'd be interested to hear from you.

...-.- de m0xpd

Gyrator Analysis 2

Recently I posted an analysis of a circuit called a "Gyrator" - only to realize that it was wrong! I'm interested in the gyrator having used it in a design for an active CW Filter, recently published in SPRAT.

Fortunately, I spotted my mistake before suffering the indignity of having somebody point it out and I updated the original post with a warning that the so-called "analysis" was nonsense. I also promised to correct it - so here we go...

The circuit under consideration is shown in the image below...

We start the analysis by noting that the voltage at the non-inverting input to the op-amp can be related to the input voltage using the potential divider equation (it was at this stage I made one of the dumb mistakes in my previous botched analysis)...


Ideal operation of the op-amp (which here is set up as a voltage follower) will force the voltage difference between the inputs to zero, such that...


We're now ready to solve for the two currents i1 and i2 – we start with i1


Substituting for the voltage at the non-inverting input gives...


(Microsoft's Equation Editor has done a pretty poor job of laying out this equation - but life is rather too short to do anything about it!!)

Next we turn our attention to i2
...


Now we have both currents, we're able to solve for the input impedance of the circuit ...


which is solved by substituting our solutions for the two currents...


A little boring algebraic manipulation gives...


and a little more yields a more useful form for the "final" result...


This impedance is that of a series combination of resistor and inductor, with another resistor "shunting" the inductor, as shown in this equivalent circuit...


The Gyrator is seen to emulate a "virtual inductor" having value L = (R2-R1)R1C, in series with a resistor Rs = R1, shunted by a resistor Rshunt=R2-R1. This virtual inductor can easily have large value - a value so high as to be impractical to achieve using a physical inductor.

Simplistic descriptions of the Gyrator have an approximate solution for the "virtual inductor" (which is the same as that presented in my erroneous "analysis") but miss the shunt resistance. In practical cases, R2 >> R1, such that the simple solution is a very good approximation of the correct analysis presented here. But that's no excuse - an analysis (even one published in such informal surroundings as this blog) must be right.

QED Hi Hi

...-.- de m0xpd