Electronic Experimentation (Spiralling Off . . .)

I wish now to relate something of the pleasure which can be experienced whilst carrying out simple experiments.

The Nutty Professor is at it again ! ! !

As many who experiment with home construction would no doubt relate, one thing quite often leads to another, which in turn leads to another, and so on (or to misquote a line from the "Commitments" movie - they go "spiralling off").

It's a wonderful thing on the whole, but one of the frustrations with it is that one never seems to get anything quite finished!

Readers of earlier blog entries will have spotted references to crystal controlled transmitters and receivers for use with the QRSS aspect of the amateur radio hobby.

Successful (one hesitates to say "the best" as this implies some sort of competition, and I don't think QRSS folk are particularly competitive) QRSS stations, whether simple or complex have to be well engineered.

Sloppy engineering practice soon becomes evident, manifesting itself in unreliability or in poor performance, and the poor performance I am thinking of in particular is that of frequency stability, or rather the lack of it.

My own home made efforts have exhibited acceptable, if not outstanding stability, and one quickly looks to ways of improving performance.

For some time now I have been pondering this issue, and a chance visit to a rather interesting web site produced a nicely written article explaining how to make a simple crystal heater
.
Thermostatic control of the temperature of the crystal used to produce the QRSS signal, or local oscillator in the case of a receiver seems to be a fairly obvious thing to do, and I had already looked at a commercial offering which offers high stability for a few pounds, and is a microcontroller based solution.

The heater to which I am referring though is a much simpler affair using a darlington transistor to modulate the flow of current through some low value resistors (the heating elements), with a thermistor to provide regulation and feedback.

This struck me as a brilliantly simple idea, so I resolved to build something similar if not quite identical.

With the exception of the thermistor, all parts came out of my junk box, in fact the darlington transistor was concocted from a small power transistor rescued from some long-forgotten project (the leads had been cut and had traces of old solder on them) and a low power Japanese 2SC something-or-other freshly removed from a scrap board which was probably a transistor radio or portable TV 20-odd years ago. Total cost of parts, probably quite a bit less than a pound.

The crystal being thermally controlled (heated) is physically but not electrically connected to a heated piece of thin tinplate (formerly part of a screening can also rescued from a scrap board).

When connected up to a power supply, my little heater worked first time (it is so simple it could hardly fail), and after some experimentation with the settings I had it heated up to just under 40 deg C, and was able to adjust the crystal FREQUENCY (the crystal was electrically connected to a completely separate test oscillator) by tweaking the temperature of the heater. The heater once it reached equilibrium maintained its set temperature perfectly.


My test set up involved monitoring the current drawn by the circuit, and the collector voltage of the transistor.

Pretty it ain't - interesting it certainly is!

Inspection of the circuit shows that they go in opposite directions - when the collector is high, the current drawn (and therefore the power being dissipated in the heater resistors) is low, and vice versa. If the surroundings change, or the circuit is heated up or cooled down deliberately the circuitry compensates for the changes very quickly thus restoring equilibrium.

One quickly realises that this little heater is really trying in its own small way to regulate the temperature of the
whole planet, and for it to be as economical as possible, it needs to be thermally insulated as much as possible from the outside world, and a little more thought reveals that in a way this little circuit is a miniature representation of, say, a domestic dwelling where the occupants try to maintain a comfortable temperature inside when the weather may be up to all sorts of tricks on the outside.

The heater schematic

Fascinating.

Also, as I have an interest in the application of microcontrollers, this application is also, as stated above, one where a microcontroller could be used, but this is where one needs to think about cost. Even buying new components, the unit cost of my little device would be no more than a pound, and the cheapest microcontrollers cost in the region of 75 pence per unit, so by the time you've bolted any additional components required, the simple version probably wins out, but only just. Die hard microcontroller enthusiasts would probably dispute that assertion!
Either way the mere consideration of one approach versus the other illustrates perfectly how experimentation can lead one through all sorts of interesting thought processes, which is really the whole point of me writing this note.

New Year, New Ideas (or not!)

I don't think I am capable of "Original Thought".

Every time I think I have discovered something new, I realise that I am re-inventing the wheel.

Please don't think I am bitter about this, if I have a philosophy in life it would be a misquote (no blasphemy intended!) of one of the "Ten Commandments" (or to be more specific the Tenth Commandment) in that I do not (or at least try very hard not to) covet what another has.

Wives, possessions, original ideas, it's all the same thing to me!  Coveting like resistance (misquoting the Borg this time) is futile.

A couple of weeks ago, a professional colleague who works at our Head Office, unlike me who works "out in the field" mentioned something called an "Arduino" to me, and I had to confess that I'd never heard of it.

Anyway, to cut a long story short I looked "Arduino" up on the web, got very excited (!) at what I saw, bought one, faffed about with it and began asking friends and other colleagues if they knew about this wonderful piece of gadgetry, and it seems that I was the only one who thought it was something "new"!

Largely thanks to my friend and mentor, Ron Taylor (G4GXO) of Cumbria Designs, I had been introduced to the world of microcontrollers some little time ago, in connection with the "Eden 9" project.  For those who don't know, the Arduino is essentially a "mini microcontroller development board" based around an Atmel microcontroller, and as such could be described as a "microcontroller on steroids".

Further research, and reading of other bloggers' output revealed that Arduino isn't the only contender in this market place, Julian,  G4ILO has blogged about the "Gadget Gangster Propeller USB" platform, which seems, at least to the casual observer to be more or less the same thing but done with different hardware.

The unfortunate thing for me is that I now have ANOTHER interest to compete for my limited free time with QRSS, meteor observations, Digimodes, Classic Rigs, etc etc.   If only I could afford to retire from the Day Job and play with all these new toys!

RC-14 - An Old Project Revisited

Way back in June 1987, the RSGB published an article in RadCom describing the "RC-14", a relatively simple "beginners" single band (20m) direct conversion receiver.    This was "kitted" by the then popular "Cirkit" emporium, and was offered at an attractive price to RSGB members.

This was, in my view a very well designed piece of equipment, and contained only three integrated circuits (one of the famous and rather splendid Plessey "SL" ICs and a couple of op amps configured as active filters with characteristics very similar to those of a high-performance crystal SSB filter) plus a varactor-tuned VFO, and the end result was a very pleasing receiver.

I built the receiver not long after it was published using the approved kit, and adapted it to my "bespoke" requirements - I disliked the flimsy enclosure provided and moved it to a more mechanically sound but less aesthetically pleasing aluminium die-cast box, and replaced the linear slider tuning pot (remember it was a varactor based design) with a rotary multiturn unit, albeit at great expense, and used it for a while (as you do) and moved on . . .

My version of the RSGB RC-14

Recently, I have become interested in the "QRSS" aspect of the hobby which is based around the transmission of very low power, low signalling rate beacon signals for extended periods which are received at various locations around the globe using PC-based "grabber" software.

Participation in this requires either the setting up of a "grabber" receiving station, or the use of a low power "MEPT" (Manned Experimental Propagation Transmitter), or in some cases both, though not necessarily at the same time!

Over the last few weeks I have been doing either and even occasionally both (!) using conventional equipment, and by "conventional" I mean "High Performance Japanese Transceivers", certainly as the receiving station, but it occurred to me recently that it was possible overkill using such high-spec equipment to perform such relatively mundane tasks.   In a flash of inspiration (or something!) I remembered my RC-14, and began to wonder if that could be dragooned into service as a QRSS receiver.

The built-in VFO, though adequate for general receiving purposes was certainly not of the required specification as a QRSS receiver, where frequency stability is a primary requirement, but the substitution of the built-in VFO with a crystal-based, or even synthesiser-based local oscillator would seem to be a Good Idea.

If you are following the argument, then by now you will surely have picked up on the mental thread . . .

And so, another project is born!

A New (Old) Direct Conversion Receiver

For a while now I've been participating in the "QRSS" aspect of the hobby, mainly by streaming my "grabber" or sometimes "grabbers" (I can run two simultaneously if I am feeling keen!).

Each of these grabbers ties up a radio and a PC.   As you may have realised I have quite a number of each of these commodities, a ridiculous number, if you were to ask my wife, but being brought up in post-rationing Yorkshire (though not of such Noble birth), I always felt that tying up a sophisticated multi-band multi-mode transceiver just to stream a Spectrum Laboratory grab onto the Internet was "overkill".

I've been pondering for some time knocking up a direct conversion receiver for, say, 10MHz which happens to be the most popular band with QRSS enthusiast.  I've built a few of DC receivers over the years.  They tend to be fairly "minimalist" devices, and yesterday it struck me in a flash that I have already got, gathering dust on a shelf, a 14MHz single-band receiver built back in the 1980s which would potentially fit the bill.

The receiver in question was dubbed the "RC-14", and was a project featured in Rad Com back in 1987, described as a "beginners receiver".   When built at the time it worked reasonably well, and I reworked it slightly to fit it into on of those ubiquitous die cast boxes as the one which came with the Cirkit (remember them?) kit was rather flimsy to say the least.  In my opinion, the nicest feature of that particular design by Steve Price GW4BWE was the AF stage which featured a nice two stage active low pass filter'  The performance of this filter meant that the radio sounded like a "proper" SSB receiver, when the received signal was strong and in the clear.

It hasn't had a great deal of use since then and it occurred to me yesterday that it would be relatively straightforward to "wavechange" it to the 30m band.

QRSS stations tend to operate around a single 200Hz channel either side of 10.140MHz, and just below the WSPR segment.   In  view of this, simply moving the built-in 14MHz VFO to 10.1MHz would probably not be the best thing to do.  Instead a fixed oscillator on the right frequency would fit the bill, or maybe a "VXO" to give a little more operational flexibility.

Now I haven't got a suitable 10.14MHz - ish crystal to hand at the moment, but as proof of concept I have temporarily modified the radio to accept an external oscillator, and used a synthesised signal generator as that external oscillator tuned to 10.1387MHz instead.   This puts the wanted frequency of 10.14 plus or minus right in the middle of the receiver pass band.  A slight tweak to the receiver's input tuned circuit was all that was needed to get the receiver up and running, and in this way I've been streaming this new (old) grabber receiver onto the Internet all afternoon with satisfactory results.

I am now wondering at the practicability of using this principle as the basis for a two or possibly three band dedicated QRSS receiver.  And so another project is born!

Good News, Bad News

First the Good News.

I believe the PC which was whacked by a virus/trojan/bot last weekend, courtesy of a "driver site" is now back up and running having been seemingly "de-loused".

As it was still partially crippled, even after a Windows XP "repair" from the OEM CD, whilst I was driving up to the top of Scotland at the beginning of the last working week I figured that one way of dealing with the problem was to connect the affected PC's hard drive as an additional drive to a fully functioning PC, and to virus scan it from that PC.

This is what I did yesterday, and the virus scan found a few suspect files and zapped them.

Once the "cleansed" drive was reconnected to its proper PC and that was booted, it was immediately evident that the nasties had in fact been purged.

I then fixed the on board virus checker (this PC runs Microsoft Security Essentials) with a "hotfix" downloaded from Microsoft, and then let Windows Updater catch up with everything, including re-installing Service Pack 3.

I took the opportunity to vacuum out the PC, a Dell Dimension 3100, which always has been blissfully quiet and generally tidy up all the cabling associated with it, no trivial job I can assure you!

Anyhow, it all seems to be in reasonably fettle now, and I have once again started up my QRSS grabber, though I think I won't reinstate the Apache Web Server.

As part of the rescuing of the situation I moved all affected sites off site, and I will leave them there for the moment.

Now the Bad News.

On a whim, I extracted my TS-180S from the shed with a view to giving it a little exercise as it has been lying discarded for a few months.

To my horror upon firing it up I found I once again had a "dead" digital display.   The receiver is still working as it was when I put it to one side, but when last used it had a fully functioning display.   My favoured theory at the moment is that I disturbed some wiring when I tidied it all up before putting the covers on.  

Knowing the previous track record of this radio, that might be wishful thinking!

Bother ... !!

QRSS - And More on the Fascination with Propagation

I would be the first to admit that I'm a bit of an "odd fish".   Regarding my radio on-air activities I am most content just lurking in the background, listening and watching and taking note of what goes on whilst my transmitting activities are very sporadic.

I accept that in a way this is quite a selfish attitude - if all the other enthusiasts in the world did what I did, there would be very little for those like me to listen to!

Thankfully, we are all just that bit different, and the mathematics of probability dictate that the mainstream provides the required fodder for practically all of us.

However what I have learned to do over recent years is to make a contribution to the world of Amateur Radio in another way, by uploading information to the Internet in such a way that fellow enthusiasts can make use of it.

There are many ways of making this kind of contribution, all you need is a computer or computers, an Internet connection, and software which allows the uploading of information automatically.  There are a number of ways of doing this, each serving its own particular niche interest.

One I have been doing for quite a long time now is participating in the WSPR (Weak Signal Propagation Reporting) network.   This is actually one activity in which I make a regular transmitting contribution though that isn't essential.

One I have started to make a contribution to more recently is the self-administered network of QRSS enthusiasts.

For those not in the know, QRSS, which has been around for a number of years is a very slow signalling system, usually our old friend Morse Code but sent VERY slowly, used to modulate very low power (usually less than one watt) transmitters, and the reception of these transmitters is recorded using a suitable piece of DSP-based software, and the screen displays of these programs are uploaded to the Internet where they can be seen by interested parties.   The web pages displaying these are known as "grabbers"  Claudio, I2NDT maintains a web page of links to many of these "grabbers" - he calls it his "Compendium" and I would encourage you to click on the link to have a look.  In QRSS terminology, these low power transmitters are often referred to as "MEPTs" (Manned Experimental Propagation Transmitters) to distinguish them from "Beacon" transmitters, as there are licensing issues with the use of the latter terminology in some parts of the world.

I have built a little web page showing my own contribution to this system which can be found HERE. This will only be active for some of the time, as it does tie up equipment, but when it is active I make an announcement on the "KnightsQRSS" EMailing list, likewise when it is shut down.

I also have on the bench as a construction project a little QRSS transmitter from a QRP Labs (brainchild of Hans Summers, G0UPL) which will hopefully take to the airwaves on 30m very soon.  This will use my alternate callsign of G8LBT which, in Morse Code terms has a more even distribution of dots and dashes, and should, I think be slightly more useful as a QRSS source.

Expect more Blog contributions relating to this fascinating arm of the hobby, and in the meantime if you want to have a look for yourself at "live" QRSS transmissions, I would suggest you dial in either 7.000MHz USB or 10.139MHz USB into your HF receiver, and feed the output into a PC soundcard, and run appropriate FREE software such as ARGO or Spectran (my personal favourite is Spectrum Laboratory by DL4YHF), and see what crawls across your PC screen. www.weaksignals.com/ is one good source, as is DL4YHF's page if you want to download Spectrum Laboratory.