A (Christmas) Magic Smoke Event . . .

I have recently been giving one of my "old ladies" in the guise of my 1982 vintage FT-101ZD Mk3 a "run out", promoting it to "main station rig" status for a few days despite the fact that I am aware that it is still in far from perfect working order.

It's basically a nice set, so that was no major sacrifice.

However, after the radio had been on for a few hours I suddenly started to get a distinct smell of "something" from it. I've smelt very many electronic faults in my time, but this one seemed rather to smell of a pan on the stove burning dry, but I quickly realised that there was no pan on the stove in the kitchen, and that the smell was indeed coming from my '101.

I removed the power and found a flashlight so I could investigate the cause, and spotted a little plume of smoke emanating from the left hand rear of the rig, and I also noticed that this corner of the rig seemed to be rather warmer than normal.

Straight away I disconnected all the external cabling, and, having allowed a reasonable time for the internal high tension power supply to discharge, I removed the top cover thinking that the sooner I could get at the innards, the more likely I was to identify the source of the problem.

Thus I homed in on the "Rectifier B" board and quickly spotted a rather distressed looking electrolytic capacitor which also seemed to be unusually warm to the touch.

Rectifier B Board in situ - PB-1968B

Now it may be recalled that this radio, bought originally as a “spares or repair” item from EBay, has had a chequered history having done questionable service as a high powered and illegal CB rig. It had no doubt been abused, quite possibly by someone less educated in the finer arts of the tuning and conservation of valve/hybrid rigs, this abuse being most keenly felt by the power supply stages. I had already rebuilt the “Rectifier A” board which had expired completely, and it now appears that I should have paid rather more attention to the “Rectifier B” board, which supplies screen and grid bias supplies to the output stages.

My own fault and hopefully any collateral damage will be minimal.   Looking on the bright side, as one of my “Twitterati” so nicely put it, at least it was “Christmas Magic Smoke”!

Huff and Puff Stabilisers - they really DO work!

In an earlier post I alluded to the fact that I was building an X-lock by Cumbria Designs with a view to incorporating it into my 30-year-old Yaesu FT-107M as that particular radio has (or had) a bad case of "driftitis".

X-Lock is a software based derivation of the "Huff and Puff" oscillator stabilisation technique whereby the frequency of an oscillator is sampled, compared with a crystal or other high stability reference, sampled again and frequency nudged in the opposite direction to any detected drift.

A couple of sessions with the soldering iron saw the kit completed without any issues, and then followed quite a bit of "circuit-bashing" (study of schematics!) plus reading up of other implementations of X-lock into old equipment.   After all this I had on the back of an envelope a plan for interfacing the two pieces of equipment.

Last weekend I lashed up a test which looked promising, and finally, this weekend the project was completed and I now have an "X-locked FT-107M".

The X-lock fits very snugly into the radio, and all of my interconnections are such that no mechanical or electrical changes have been made, and it could all be removed without a trace, if required.

This will all be written up properly in due course and posted on my web site - here and now isn't the place for detailed explanations, but the following two "Argo" screen grabs illustrate just how effective the unit is on received signals.

They both show reception of the 14MHz beacon IW3ICH and were grabbed withing minutes of each other, one with X-lock controlling the frequency, and the other with just the bog-standard built-in circuitry in control.

The above trace is with X-lock disconnected, in other words how the "vanilla" FT-107M performs even after the radio has been powered for some considerable time.

Now look at the same signal with X-lock in charge :-

I would say that's quite an astonishing result and the screen grabs speak for themselves!

One of my long-term objectives has been to improve the frequency stabilityh performance, if possible of my old radio gear to the point where they could be used without any embarrassment on modern modes such as WSPR, and I would say that the X-locked FT-107M is now "good to go" on WSPR.  I just might try it today ...

Radio Prague - Another R.I.P., I'm Afraid ...

I don't really want to appear to be a "doom and gloom merchant", but a chance series of events caused me to learn that we (shortwave listeners) are about to lose another source of programming on shortwave, that of the very well known and respected "Radio Prague".

The sequence of events to which I refer started with the fitting of a 6kHz AM filter to one of my "classic" old transceivers, my FT-107M.

The filter was acquired from a fellow amateur who had acquired an FT-101ZD complete with said filter, but who wanted to return it to its "factory condition". For those not in the know, the FT-101ZD though equipped with AM facilities (a special board had to be acquired) had a rather lame implementation of this mode due to the way the "IF Shift" was connected (long story). The bottom line of this tale was that this particular FT-101ZD owner and myself eventually figured out what the previous owner had done and the modification was successfully undone, and the grateful new owner awarded me the unwanted AM filter as my reward!

This was a mutually acceptable arrangement, and today was the day I decided I would fit this filter to my FT-107M, as that particular radio implements the AM mode "properly".

The fitting of the filter to this radio was simplicity itself, and when it was done I decided to have a little tune around the 7MHz, or "41 metre" band looking for broadcast signals.

In early morning there is no shortage of strong signals from Europe, and before long I found myself listening to Radio Prague on 7.345MHz for the umpteenth time in my life.

As is usual these days shortly before the radio station closed down its English broadcast the announcer gave out some information about how to find Radio Prague on the Web (www.radio.cz), and a few minutes later I surfed into that very web site, like one does.

To my dismay my eyes alighted straight away onto a piece entitled "Radio Prague's shortwave broadcasting to end on January 31, 2011", the content of the article citing budget cuts as the reason why.

Now, the economics of shortwave broadcasting are a subject not unknown to me, as earlier in my life I worked in this medium, and was familiar enough with costs due to the fact that I actually signed cheques payable to the Regional Electricity Company who supplied the power to a major shortwave broadcasting station! Been there, done that, got the T-shirt ...

What I could never really relate to was the "value" in such broadcasting, as, being a Brit, I only ever was a "hobby" consumer of this medium. I was always told that overseas things were very different, and the average man-in-the street relied on shortwave to bring him news just as much, if not more so as he relied on his daily newspaper. I am sure this has been very true, but I wonder whether it is still true. I strongly suspect that it isn't, generally speaking, and, logically, many other broadcasting stations will soon be going the way of Radio Prague.

I would say, therefore, "enjoy them while you can" !

Classic Hybrids and WSPR and ...

A very interesting thread has sprung up on the "Fox Tango" Yahoo group prompted by an Italian amateur with an interest like mine in classic hybrid radios - in his case a Yaesu FT-901.

Apparently his radio developed a couple of faults, in particular the failure of the 6V regulator which feeds (inter alia) the DC supply to the VFO circuit.

Not surprisingly the original IC regulator is obsolete, and having nothing else to hand he replaced the faulty one with a bog-standard 7805 unit, and even though the previous 6V supply is now only 5V he claims that the VFO is now "rock solid".

You will realise from my www.g4fui.com web site that old radios are also an interest in mine, and it so happens that over the last couple of days I have been looking at the performance of my own FT-902DM and in particular the VFO stability (or rather the LACK of VFO stability) of this particular set.

I had been musing upon the supply regulation to the VFO as it appears that the real problem is that the VFO drifts as the set warms up, and as it is a bulky, heavy radio it really NEVER warms up properly (not in a reasonable operating period anyway), consequently it NEVER stops drifting.

It drifts so much that you couldn't use it sensibly for a mode such as WSPR.

I had come up with a theory that the original regulator, which claims to be a "low drop-out" device (ie it will work with the input and output voltages relatively close together, really was working just TOO close to the wire with only a theoretical 8V input being regulated to 6V out, such that the thermal changes in the environment were affecting the output volage to a significant extent.

Having a bunch of 7805s kicking around in my junk box, I just might give this a try. OK the output voltage may be significantly lower, but assuming any static frequency change can be trimmed out, the extra volt of dropout voltage, coupled with a more modern device may well make a noticeable difference to the performance.

Another contributor to the same thread suggested putting a diode in the common lead of the 7805 to lift the output voltage, but I would be tempted to try it without as (a) it would reduce the dropout voltage and (b) I suspect that the temperature coefficient of the diode would exacerbate the drift problem. Having said that, it would be very interesting to find out!

Another alternative would be to fit a 7806, and possibly take the input voltage from somewhere else, eg a 12V or similar rail in the radio.

Another item added to my "to do" list, so watch this space!