This time I’d like to talk about Small Transmitting Loop aerials, or STL’s which are alternatively known by some as magnetic loop antennas.  A loop trades size for bandwidth (the lack of!). You’ll remember the old saying, ‘Small, efficient, Broadband’. Pick any Two.

The STL is small and farly efficient for such a small device, but trades bandwidth to achieve that small size.  An aerial with a narrow bandwidth inevitably comes with a high Q.  This makes for sharp tuning, but this ‘disadvantage’ also brings some benefits. Because the STL is a sharply tuned circuit, it rejects unwanted signals, and can therefore be of use in a noisy domestic environment.

So back to STL’s. I’ve built many over the years and I’ve found that the thicker you make the radiator element, the better it tends to work. I’ve built loops from wire, microbore pipe, 15 & 22mm copper pipe among other things, but my strangest creation was done for a bet.

While tidying up the back garden, I hapened across an old bike wheel I’d junked a few years previously, but kept in case it could be ‘useful’. I’d banjoed a rather large pothole in the street which had bent the wheel rim out of true by a considerable amount, rendering the wheel useless.  I bet Paul,  MM6PMC, that I could make some sort of functional radio aerial out of the trashed wheel, and so was hatched the plan for a ‘wheelrial’, an STL made from a bike wheel.  By this time, even I was a bit dubious that I could make it work at all well.

I used a chunky pair of old pliers to snip through all the wheel spokes. and removed the hub and remaining spoke parts so I had a plain wheel rim.  I next scrubbed all the grime off it with a tub of hot water and Fairy Liquid to get all the ‘gunk’ and green slime off it. I dried the rim then took a hacksaw to the point where the ends of the metal hoop forming the rim were joined. Rims are usually pinned and welded.  Having cut a slot, I riveted a piece of single-sided  fibreglass printed-circuit-board across the gap as a strengthener.  I sanded off the copper to create an insulating gap of about 6mm in the copper of the PCB. Next I need a tuning capacitor.  A handy 500+500pf from the junkbox was pressed into service with only the stator plates of both sections connected to the ends of the loop by paralleled strands of heavy copper wire formed into a couple of links to solder both stators to the remaining copper on the PCB..  The capacitor needed some physical support, so a varnished piece of stripwood drilled and bolted to the rim provides this. The capacitor was simply ty-wrapped to the wooden strip.

Next I needed a means of feeding the loop. My personal preference is for the Gamma Match. Although not a balanced match, it does seem to work well for me with loops, better than Faraday loops or ferrite transformer feeds.

I riveted a square SO-239 chassis socket to the bottom-most part of the loop where of course there will be a current node. From the centre-pin of the SO-239, I fitted a Gamma arm made of 8mm copper micro-bore pipe. I made the arm about a quarter of a turn in length and used a shorting strap made from the same pipe to find the ‘sweet spot’ on the radiator where the reflected power was at a minimum. This is usually about an eigth of a turn away from the ‘earthy’ point in the aerial. With the ‘sweet-spot’ located…. I used plastic spring clothes pegs to hold the shorting-bar in place as I moved it around…. I marked the position, then drilled the shorting bar and rim to take yet another pop-rivet. Where the shorting bar met the gamma arm., I simply soldered the two together. I sawed off the remainder of the protruding gamma arm and was ready to test the aerial.

Bike Wheel aerial.

For testing, I placed the aerial over a piece of wood placed on top of the wardrobe in the spare bedroom and sat my guitar + case on top of it to provide support. I hooked the aerial loop over the protruding wood and connected a patch lead to it. I connected the other end to my FT817 and tuned the aerial for maximum signal on 20M. I put out a CQ call and immediately made contact with an Irish station.  Seems that 2.5W or RF into a bike wheel does indeed go!

Even at puny QRP levels, very high voltages are present in a small loop such as this and they should be treated with care. In addition to the voltages across the tuning capacitor, ther are very considerable RF circulating currents in the loop. This is one reason why fat loops work better than thin ones. Variable capacitors with sliding contacts are not ideal because of the currents involved but I’ve found that a 500+500pf varaiable with only sthe stators connected works very well. In such a situation, the lossy wiper contact is not needed and is of no consequence while the capacitance is halved and the voltage rating of the capacitor is effectively doubled.

I did a few tests on this aerial using the time-honoured trick of using a fluorescent lamp to ;sniff’ for RF.  I used a CFL (one of those coiled low-energy lamps) to ‘sniff’ the field around the loop.  Even my puny 2.5W from the FT817 running on pen-lite batteries would light the CFL to almost full brilliance when held anywhere near the tuning capacitor. I was pretty surprised at that!  The loop has proved to be robust and easily transportable… so long as you always remember to close the capacitor vanes.  It can be thrown in the back of a car, taken to a site and supported on a cheap fishing pole for use. Always carry Ty-Wraps so you can ty-wrap your fishing-pole to a handy wooden fence-post!  You need to be able to tune the loop, so the next paragraph gives a method.

Of course a tiny loop like this can’t compete with a full sized dipole and 0.5Lambda high, but if you live in a flat or a cramped place or the neighbours throw a wobbler at the mere sight of an aerial, this could be for you. The big downside of high Q aerials is the constant need to ‘re-tune’ when you move a few tens of Kc/s in any direction. It’a rather easy to add motorised tuning of course. Just a 12V DC motor run from a much lower voltage and connected via a high-ratio gearbox will work. I find the motors sold in our model shop work fine. made by COMO and they include a front-mounted gearbox. Buy the highest gear ratio you can find! Such loops tune very sharply, a clear indication of their high Q.

Well, I hope you enjoyed reading this.  I encourage feedback and comments from readers. Tune in soon for more fun & mayhem.

73 Al

GM1SXX

Alter repairing the FT102, I’d like to pass on some info about a good UK supplier of parts.

This is Audiocap, a company who supply capacitors for high Quality amplifiers of the Audio sort.

The specific capacitors I chose were 150uF / 500V DC rated types of 32mm diameter, which nicely fit the capacitor clips in Yaesu radios. I believe Trio/Kenwood use the same size caps but if you are buying for a Trio/Kenwood please double check the diameter before ordering.

The photo above is of the capacitor type I used.  They actually cost less than the Canadian imported ones I’d used and which failed, and which appear to be Chinese.

http://www.audiocap.co.uk/ft-150uf–500v-high-voltage-can-electrolytic-302-p.asp

The German capacitors are about three times the height of the ‘Canadian’ ones and slightly taller than the Yaesu originals.  I should also say that Yaesu and Kenwood radios employ 470K bleed resistors across the smoothing capacitors.  Those bleed resistors are *essential* safety-critical items and if you replace the capacitors, you should likewise replace the bleed resistors with new ones rated at 470Kilohms and a MINIMUM power rating of 2 Watts.  5W is preferable.

The resistors each have around 450V across them, so miniature types are NOT suitable.  If you can find decent 470K / 5W resistors, even better.  Just remember that your life could depend on these resistors working as they should, if you ever have to work on your radio.

I speak from bitter past experience here. Unknown to me, the original carbon bleed resistors in my radio had failed open-circuit and one day when I worked on the radio, I forgot to discharge the capacitors with my chicken-stick.  While turning the radio over (it’s a heavy beast!) I accidentally contacted the  900V DC supply with my right thumb. The current flowed into my thumb and out my right hand to chassis and blew a hole in my thumb at the top-most joint. I didn’t drop the radio!  I put it down on the bench and looked at my thumb where black smoke was still issuing from a puncture wound. I got VERY lucky that day, because the current flow was *only* through my hand.  The injury took many weeks to heal and I couldn’t bend my thumb at all for about a fortnight.  Thats the sort of thing that happens, if you are really lucky…. when you mess with 900 Volts. After I got zapped, I measured the voltage across the filter capacitors and was astounded to find it was sitting at 850V DC!  had the current path been from hand to hand, I probably wouldn’t be around now to warn you of the dangers.

I did take a photo of the damage to my thumb at the time, but I don’t seem to be able to find it. If I do, I’ll post it here.

This sort of thing should adequately demonstrate the importance of having good working bleed resistors. Old carbon composition resistors tend to drift high in value with age, and if your bleed resistors are of this type, treat them with extreme suspicion, or better still, replace them with adequately rated metal film types.

Until next time, 73.

AL GM1SXX

I’ve been rather busy at work of late and unfortunately for me, my much loved FT102 went U/S.  I didn’t really have the time to fix it until recently, so instead I’ve been using my backup radio, the TS820 described earlier.

FT102 Transceiver

The FT102 had developed a serious fault in the plate power supply and was blowing fuses. This of course is a nightmare for any FT102 owner.On a 240V AC supply, the FT102 needs a 3Amp QUICK-BLOW fuse.

The FT102′s Anode (Plate) supply is a simple voltage doubler circuit using 4 diodes, 4 small 470K resistors, two smoothing capacitors and a pair of 470K bleed resistors across the smoothing capacitors.  How difficult could it be?

The answer it seems is *very* difficult!  Two of the 4 diodes on the RECTB board had failed short-circuit, so I replaced them with modern replacements. I got a pack of new 3A Q/B fuses and tried again.

Loud transformer hum and the fuse blew again!  I checked everything I could and all the resistances checked out fine. I was running out of ideas now!

I disconnected the 320V AC connection at the mains transformer and tried again… fuse didn’t blow, so the fault WAS in the plate supply. I reconnected the 320V AC line.

It didn’t make sense.  All that was left was a few resistors and the two smoothing caps and all of them seemed OK.  Having run out of ideas, I ordered a new pair of smoothing capacitors and fitted them.  This time, success.  The capacitors I’d bought to replace the originals several years previously seemed to be faulty.  They measured OK on a simple resistance check but failed when high voltage was applied.

I’ve never seen a problem like this before, but I’ll sure remember it in future!  Here’s a photo of the dodgy capacitor and it’s bleed resistor.

Very strange!  A capacitor that works OK at low voltages yet fails when it’s rated voltage is applied.

I’m just happy to have the FT102 back in action again.

73 Al.

GM1SXX

Hi All,

Nicolas M1HOG has pointed out that I missed some obvious ways to get on the air cheaply, and I agree with him.  Among his suggestions are –

—————————————————————————–

Loan  equipment from your local radio club / members!   Secondhand  equipment from other club members – Well ones you trust  anyway!   Certainly  Wouxun, which you have already mentioned.   Kits – Walford, SDR and  kanga   Modifiy PMR – Some still very cheap/free and worthwhile.   Sprat – £6  per year!

—————————————————————————–

I agree Nick, and as for myself, I do have some kit equipment including Walford Electronics Midney and Kingsdon (RX and TX), plus several… OK, well a pile really of Ex PMR radios, so I can monitor miltiple bands.   PMR radios are built to high standards and can often be ‘tweaked’ to work on amateur frequencies.  It’s also possible to buy ready converted ones at attractive prices.  Common radios include the Philips/Simoco FM1000 ‘family’ of FM radios and the Storno range.    At home I have a pile of FM1000 and FM1200′s plus a Storno 6000 series radio.  All are good performers.   The Ascom SE550 is another PMR possibility.  My own thoughts are that the STORNO 6000 range of radios is in a class of their own.

Tetra are a well-known UK purveyor of ex-PMR radios.  http://tetra.co/  There are many others too.  Converted radios also appear from time to time on EBay. Sometimes a look under the covers reveals the original owner.  One of my radios originally belonged to the Dutch Fire Service while another was more local, having been fitted in a council van!   For those with the ability to reprogram EPROMs and do general radio work, there are bargains to be had with unconverted FM PMR radios while for the ‘appliance operator’ these radios can be bought for a fraction of their original cost.   Denis PA4DEN seems to have been responsible for a lot of the work needed in converting the Philips/Simoco FM1200 radios to the amateur bands.

http://www.pa4den.nl/fm1200.html  Some of my own radios have PA4DEN control EPROMS fitted.

Club Loans   Some amateur radio clubs have loan equipment avalable to members. This may be a route to take initially until you find your feet.

The kit approach.   For those competent at soldering and kit construction, there’s the excellent MKARS80 which is an 80Metre SSB transceiver kit while other radio kits are available from overseas.   The MKARS80 is a fine little single conversion transceiver with a huff-puff stabilised VFO and PIC based frequency readout.  For the keen constructor, it’s a real bargain.  Mine is built into a plastic electrical equipment box fitted with a clear lid and internal Lithium rechargeable batteries. It only needs a headset and aerial and earth added to get on the air.  Very portable and lightweight.

At home I also have a part finished BITx20 transceiver.    http://www.radio-kits.co.uk/   http://www.qrpkits.com/bitx20a.html

For those who favour QRP operation, and that includes me, there’s the excellent G-QRP group with their magazine Sprat.  I recommend joining the G-QRP group if you have *any* interest in low power operation.

http://www.gqrp.com/

More recently I bought an 80Metre Finningly receiver kit. The Finningley is an SDR (Software Defined Radio) and uses the power of a PC via a soundcard connection to do the signal decoding. This allows a great deal of flexibility, but of course ties up a PC.

Finally, My much loved FT102 threw a hissy fit, made a LOUD buzzing noise, and before I could reach the on/off switch, popped it’s 3 amp fuse!  I’ve traced the problem to the HT section by disconnecting the 320V AC line from the power transformer to the HT voltage rectifier/multiplier.  It’s likely that one of the PSU diodes has failed short-circuit or thePA  anode to Pi-Tank coupling capacitor has gone short-circuit.   I’m sure it can be fixed, but for the moment, it’s PLAN B… using my TS820S instead. The TS820S is a lovely old radio, but is missing the WARC bands, so wish me luck in repairing my FT102.

Until next time…. 73   AL GM1SXX

Today I’d like to talk money.  Not big money, mind you, but the sort of money that many of us could afford, like say £100.  Now, what could you buy for a hundred quid these days?  Well, certainly not a shiny new radio from Kenwood, Icom or Yaesu but of course you could buy a perfectly fine new Wouxun dual band handy for that sort of money, very useful for out and about, and with an external aerial, perhaps some SOTA activity.

But when it comes to HF radio, a hundred quid won’t buy you much… or would it?  I have to admit to having a very well equipped shack here but none of my radios are very modern.  Until I bought an FT817ND a few years ago, my most ‘modern’ radio was an FT290 MK1 bought in 1986!

In the shack, my most used radios are my much loved FT102 and it’s standby radio, a Trio TS820.  Both of these excellent radios were purchased for under 100 Pounds (each).

The FT102 was purchased as ‘known dead on transmit’ from a radio rally.  £5 worth of parts, to repair the driver stage,  had it back up and running again.  It helpsgreatly  if you have the technical knowledge to be able to repair and maintain your own radios, surely a strong incentive to go for a full license and to study as much as you can.  Failing that, it helps to have a friend with the requisite knowledge who can help.  Since repairing the FT102, I have changed out virtually all the relays in it and it performs excellently.   It sees daily use.

The TS-820S was also bought from a rally, for 90 Pounds. It came to me looking rather neglected and grubby but all the screws were in place and none were ‘chewed’. A positive sign.  I gave it the ‘all important’ ‘sniff test’ looking for anything burned or the presence of tobacco smoke (which kills radios!). I checked all the controls for smoothness and it was apparent that the VFO needed some attention.  It smelt ‘neutral’, so I bought it and took it home.

Set up on the bench it was obvious that this was a fully working radio. Apart from being grubby and having a sticky VFO knob, it was in pretty good shape, but transmit power was a bit down on what I’d have expected.  I removed the sheet metal covers and thoroughly cleaned them with AF spray foam cleaner.  They were in near pristine condition under all that ‘grot’.   I removed all the control knobs and used the same cleaner to clean the front panel, spraying cleaner onto a soft cloth and using that plus cotton buds to reach awkward areas. My radio now looked almost brand new.

Next to attack the sticky VFO.  I got the service manual from the WWW and proceeded to strip out the VFO unit. It was a bit fiddly but it was obvious that the lubricant used on the bearings and spindles had dried out, hardly surprising in view of it’s age.  The original lubricant had turned into a sticky goo. All the VFO mechanical parts were carefully cleaned and re-lubricated sparingly with lithium grease and the VFO was returned to the radio. It now was silky smooth in operation.  I finished reassembling the cabinet and control knobs, and the radio looked very good indeed.

Here are a few photos of it after it’s service.

The radio actually looks better in real life than it does in the photos, for which I used flash. In reality, it’s a very clean and well cared-for radio.

Although these radios were built in the 1970′s, when I still had long hair, they still perform very well and should not be overlooked if your need is for a solid dependable HF transceiver.  They are capable of excellent performance and are fairly easy to work on and maintain.  Being ‘Hybrid’ radios… transistors and valves, high voltages are used in the driver and PA stages and you do have to be aware of that when servicing them or working on them.

Here is the basic spec of the TS820S

Type:Amateur HF transceiver
Frequency range:10-160 m + WWV
Mode:SSB/CW/FSK
RF Power output:Max 100 W
Receiver system:Single conversion superheterodyne IF: 8.83 KHz
Sensitivity:0.25 uV (10 dB S+N/N)
Selectivity:SSB: 2.4 KHz (-6 dB), 4.4 KHz (-60 dB) CW: 500 Hz (-6 dB), 1.8 KHz (-60 dB) Image rejection:N/A
Voltage:Mains (or 13.8 VDC with DC-DC option DS-1)
Current drain:RX: 0.6 A (5 A heaters on) TX: Max 15 A @ 13.8 VDC
Impedance:50-75 ohms, SO-239
Dimensions (W*H*D):335*155*340 mm

Wouldn’t look out of place today really!

Don’t let the use of valves in these radios put you off.  The 12BY7A driver valve is long obsolete, but being a TV valve can still be found second hand and generally tested, on that great E**y emporium!  The 6146B PA valves are still in production, so pose no problems at all to find. Taken proper case of, the PA valves can last the life of the radio, but the 12BY7A drivers do have a finite life in amateur radio duty where they are being deliberately over-driven to do a job they were not really designed for.  I therefore keep a small stock of 12BY7A valves to keep my old radios working.   Expect 5 years hard use from a good 12BY7A.  My TS-820S still has the original 80′s vintage S2001A PA valves (a Japanese ‘clone’ of the 6146B), and they will if asked still deliver full output. If you take care of PA valves and don’t over-drive them, they can, and will’ last a LONG time. I replaced the 12BY7A which was a bit weak, with one from my personal stash.

Bear in mind that some of these hybrid radios were made before the WARC bands (30,17 & 12M) came into being and may therefore not have these bands present.  Whether or not that matters is for you to decide. I’m a big fan of 17M so I can operate on 17M on the FT102, but not on the TS820S which doesn’t have that band.

In the case of hybrid radios, if you find the transmit power is low (and you should expect it to vary across the bands, with less power as you go UP in frequency), before you even think of replacing the PA valves, substitute a different 12BY7A driver valve, to see if that helps. In my experience, it almost always does.  As for finding operating and service manuals for old radios, there’s an absolute wealth of information on the WWW.  I get all my manuals there… for free.

If you are looking for an HF transceiver and don’t want to spend a fortune, these hybrids can fill the need. I’d also like to mention that some people I know have sold their shiny new ‘Rice Boxes’ and purchased hybrids instead.  None of them would ever be willing to return to using modern radios.  Something worth considering IMHO.  Ease of use and the lack of bells & whistles can be a big advantage for the serious operator. All the controls on the front panel and easy to use. It’s quite persuasive.

Until next time.

73 AL

GM1SXX

I hope you all had a good holiday and a Good New Year.

This time I’d  like to mention a bit about the amateur radio allocations.  I often hear complaints from radio amateurs about others who use ‘our’ radio frequencies, and no more so than from those who use amateur radio satellites.  It has to be understood that the radio spectrum is a busy place and no one group ‘owns’ frequencies within the spectrum.  Instead, The ITU (International Telecommunications Union) divides up the available spectrum space with a view to making the most of whats available.

http://life.itu.int/radioclub/rr/rindex.htm

As radio amateurs, if you look at the current bandplans for whichever IARU / ITU region YOU live in, you will see that some bands have Primary and some have Secondary status.

Having Primary status infers that WE are the primary user of that band, but one should be aware that other users may also use that band by permission of the relevant authorities, but have to accept that  they may suffer interference from Primary users… i.e. US!

Secondary status means exactly that. We are secondary users of that or those bands, and MUST accept interference from the PRIMARY users.  We also have a duty NOT to CAUSE interference to the PRIMARY users.  A case in point is the 70Cms band, where in Region 1 we are Secondary users, and so must accept interference from RADAR, Military systems and other PRIMARY users, and must not cause interference to those users.  Many amateur satellite users don’t seem to understand this. some spot frequencies on 70Cms are also used for car-locking systems and Short-range-devices.  These users also have secondary status and for example cannot reasonably make a complaint against being locked out or in their cars by RADAR and other Primary user activity, and yes, it does happen.

For 70CMs in Region 1, the following conditions apply…

So, no matter what some people think, in Region 1, we get to use 70Cms as SECONDARY Users.

More recently there have been web postings about the 23CMs band and the possibility of radio amateurs causing interference to the Galileo GPS satellites, which among other things, operate on the 23CMs band.    http://www.southgatearc.org/articles/galileo.htm

We are also SECONDARY users on 23Cms, so in addition to accepting interference from the Primary users, we must not cause interference to them.

You’ll remember the bit when you were studying to become a radio amateur which generally goes… ‘Use only as much power as is required to maintain the contact.’

Why then do I hear so many stations giving out 599 reports?  Surely a 599 report should be considered a lousy one?

Until next time.

73

AL GM1SXX

The first problem I had was a faulty 723 regulator in the -7 volt line. This was a few years ago, and because of the scarcity and cost of obtaining a replacement round canned Ua723, I chose to build an off-board regulator using a modern negative voltage adjustable regulator IC. This proved to be very easy to do and restored the radio to a working condition.  

I’ve had other problems too. The PSU is a linear type and supplies
+20, +12, +5, -1V and -7V and is fitted on a single PCB with pass transistors mounted on the rear apron of the set. If the RA1772 has any real design issues,  it’s in that PSU. It’s very cramped and being a linear type with multiple voltage regulators, runs hot, so has a tendency to ‘bake’ the wiring, leading to brittle insulation that can crack and fall off, which of course can lead to short circuits:-)

This ‘Observation’ has some large images that may take time to load.  Just be patient.

My most recent receiver fault also turned out to be PSU related.  The bridge rectifier listed as D2 on the schematic disintegrated… at least the positive output tag somehow separated from the rectifier leading to a total failure of the receiver.  D2 generates most of the heat that emanates from the PSU.  My first thought was to replace it with a potted bridge rectifier purchased from Maplin, so I proceeded to go about replacing the faulty bridge rectifier with a new one.

In the photo above, you can see the rear panel of the receiver folded down and the PSU board is just visible in the jumble of wires on the left of the photo.

Here you can see the offending rectifier as removed from the radio. The positive connection tag just lifted free  as I was about to unsolder the leads from it!

This photo shows the PSU board with the new metal cased rectifier bolted into place and ready to connect up.  The PCB pads marked ML1 are the site of the original Ua723 that was used in the -7V supply, and which I removed years ago.

In the event, I deceided to take the recfifier off-board completely, a simple matter of arranging a few flying leads from the PCB to the rectifier, in it’s new position, so the photo above is NOT how my PSU looks now!  That new metal canned rectifier has been moved!

The wiring connected to the pins at the bottom of this photo suffers badly from being ‘cooked’ over many years of use. The insulation tends to become very brittle, and the wires inside oxidise, none of which is a good thing. In the photo sandwiched between the new rectified and the small IR bridge rectifier to the right of it are some pins that have thin ‘fuse wire’ soldered across them in normal use, to provide on-board fuses for the various supply lines. There are a number of these links used in the PSU board and ALL of them must be present and correct for the radio to function. In this photo, I had removed the links.  I fitted new ones later.

I’m not sure what sort of ‘fuse wire’ RACAL used for these links, but I use a single strand of wire culled from normal stranded hookup wire as replacements.  Works fine for me!  The links protect the transformer secondaries in the event of a fault condition.

This photo shows the eventual setup I used!  Since the bridge rectifier D2 produces most of the heat generated by the PSU, I decided to take it ‘off-board’, so I unbolted it and placed some ‘copper island’ pads where the rectifier had sat, so I had convenient connection points for the new wires I installed to connect to the rectifier. The advantage of this arrangement is that I take the heat generated to another part of the radio chassis where it can’t do so much harm.  The RA1772 is very ‘tight’ for space so I had to do some thinking about where I could place the rectifier to dump the excess heat while being a safe position to avoid short circuits etc.  

Here’s another photo of the PSU area showing the main reservoir capacitors  and the PSU panel folded down.

My eventual solution was to bolt the rectifier to the rear of the card-cage that holds all the modular boards.  This has decent ventilation while providing a large surface into which the heat can be dissipated.  The wires from the rectifier are routed back to the PCB where the old one used to live. Unfortunately, I’m a bit like Henry Ford when it comes to wire colour… black, black, or err, umm… red!  Ideally I’d have preserved the RACAL wiring colour-scheme…. but where to buy grey wire with blue stripes evades me!  I used a load of small ty-wraps to tidy up the wiring and although not as nice as the original lacing-cord, it does a job of work.

The bridge was fitted below the level of the edge of the card-cage in order to clear the cage lid when it was re-fitted.

In this photo, you can see the modified PSU board and my earlier repair to the -7V supply, where I used a regulator  fitted in the space vacated by the -7V supply’s pass transistor  I ripped out along with the 723 regulator associated with the -7V line, identified on the PCB as ML1.    I used an LM337T regulator and a pair of fixed resistors and decoupling capacitors for the new -7V supply.  Because this is a non-standard mod- I also labelled it as I have now also done with the D2 rectifier.

You can see the -7V supply more clearly in the photo above. The heavy wire goes to an earth tag on the chassis. I used ‘copper island’ PCB pads cyano-glued to the heatsink to make the various connections. This repair has seen daily use for several years now without any problems.

This photo shows the relocated rectifier D2 and associated wiring. The box to the right is the RF stage, preselector etc.

The old and new rectifiers for comparison. The new one is rated at 10 amps.

Almost back together again!  You can see how little space there is around the PSU board on the left side of the photo and also how much metal is available for the rectifier to dump heat into. The rather ‘chunky’ mains transformer can be seen to the left of the photo in it’s steel box.  RACAL didn’t do things by halves. It’s a very nice varnish impregnated job, and very quiet indeed.  The grey box situated between the transformer and the front panel is the ovened 5MHz frequency reference for the synthesizer. To the left of the loudspeaker (on the rear of the front panel) you can see the 30 position band-switch. I imagine this was a ‘special’ for RACAL and it’s beautifully made. One thing you can’t see is the tuning encoder which is an optical quadrature type constructed as a bespoke item for RACAL.  It’s beautifully made and a complete delight to use. Silky smooth.

Here you can see the receiver with the card-cage screening cover  in place. The edge of the rectifier just clears the lip of the cover… whew!

Copy of the PSU PCB overlay… from the RACAL service manual.  D2 causes most of the heat (and trouble).

Back together and working. 331?  That’s the Glasgow Airport NDB navigation beacon… just for a quick test!

The unit below the 1772 receiver is the RACAL MA1720 transmitter exciter.

73 Al.

GM1SXX

Why anyone would use this amount of power on BPSK is an absolute  mystery to me. At home here, I run a couple of ancient hybrid transceivers made in the 80′s, so they are around 35 years old now.  That’s older than some operators I talk to!  The FT102 is a big beast of a radio, but to ‘tame it’ and operate ‘sensibly’ I yanked the three 8298A PA valves out of it and in place put a solitary tired old 6146B pulled from a scrapped radio. This allows the radio to generate what are ‘sensible’ power levels for BPSK working. I normally run 2-4Watts on BPSK and with that I’ve worked all over Europe and beyond, so why use more?  It’s propagation, and not power, that gets your signal from A to B:-)  I remember also in my RAE Exams back on 1985 that one thing that was expected of the candidate was ”’ to use only enough power as is required to maintain the contact.”.  Most PSK operators seems to have forgotten that one, as witnessed by the broad snotty trails splattering all over my Waterfall display that should of course be the neat ‘cats eyes’ of a correctly modulated signal.  Without a doubt, Saturdays and Sundays bring out the LIDS in their droves.

On BPSK with a simple vertical or wire aerial, I find that 5W will do almost anything I’d want.  Over the Christmas and new Year Holidays, I experimented with BPSK31 using my deliberately ‘crippled’ FT102 running power levels of 1-5 Watts.  What I found was that if 5 Watts to my lousy non-resonant DIY vertical was making the trip, 2W would do so too. Only when I backed the power off to 1W or less, did *some* stations notice. 

Because my aerial is screened by a nearby fence, causing most of the RF to be beamed Eastwards (See the BOCTOK AHTEHHA), getting out to the US is not so easy for me, but even so, I’ve worked the US on 15-20Watts under fairly poor conditions.  60W to a beam is NOT required or even desirable.  On PSK, a clean well-modulated 10W signal will do better than a 50-60Watt splattering one.  

Recently I worked Vladimir, UT5LC and by my standards, a ‘local’. It was a very easy comfortable contact running just one watt. Although the QSO says I was running 2W, the power had dropped to one, and I didn’t notice it until later. It’s obvious that Vladimir had NO problem copying me. I batted a paper QSL in his direction. 

CQ CQ CQ DE UT5LC UT5LC UT5LC
CQ CQ CQ DE UT5LC UT5LC UT5LC CQ
pse K

CQ CQ CQ DE UT5LC UT LC UT5LC
CQ CQ CQ DE UT5LC UT5LC UT5LC CQ .

CQ CQ CQ DE UT5LC UT5LC UT5LC
CQ CQ CQ DE UT5LC UT5LC UT5LC CQ
pse K

UT5LC UT5LC de GM1SXX GM1SXX Pse K

GM1SXX de tnT5LC GM1SXX de UT5LC
Good morning DR OM
Report 599 599 ,
NAME Vladimir Vladimir,
QTH IZYUM IZYUM Ukraine Ukraine ,
LOC KN89PE KN89PE RDA : HA-23
Info http://QRZ.com

HW?
GM1SXX de UT5LC pse k

Good day to you UT5LC Vladimir
UR RSQ 599. My name AL (Allan) .
Power 2 (Two) Watts.
Loc: IO75TU IO75TU. QTH: Paisley, 10Kms West of Glasgow..
Details@QRZ.COM. Logged 07:34:05z
BTU my friend Vladimir UT5LC de GM1SXX

GM1SXX de UT5LC Vladimir
Thank you for your informations dear Allan.
Good luck to you and your family!
QSL via www.eQSL.cc and bureau
Please, send me yours QSL!!!
Many thanks for this QSO.
p hope to meet You again soon in BPSK31 or in other modes.
All the best and good DX’ing
GM1SXX de UT5LC BYE BYE, 73 SK

TNX Vladimir UT5LC MNY TNX for the contact.
Hope to meet U AGN. QSL via eQSL (AG), or direct only. No BURO.
UT5LC de GM1SXX 73 Bye Bye Vladimir SK SK

GM1SXX DE UT5LC
BYE 73 SK TU Marry Chistmas and happy new year 2012

73 my friend, will post QSL card direct to you.

If we all reduced our power on PSK to sensible levels, it would be a lot more pleasant for everyone concerned.. After all, it’s what we are supposed to do, under our license conditions!

Until next time.

73 AL GM1SXX

Note the splattering powerful signals.  One was an individual station while the other was a special event station.  Note also the ‘swishers’, carriers wandering across the passband of the waterfall.  Actually, I’ve seen it a lot worse than this, but it’s bad enough, and puts the sensible guys off.  Sometimes it pays to run QRP in these conditions. Seems daft, but it often works. I think they get such a surprise at seeing a weak signal that they go back to it!  What gets me is that this sort of behaviour is not common during the week, so I can only guess that even amateur radio encourages the ‘Sunday Driver’ mentaliry in some people.  Whatever the reason, thats why I do most of my operating on weekdays.  I could earily copy the strong PSK signals above with my TS820S, without an aerial connected!

Now honestly… is there any need to run so much power?  Does nobody remember the bit in their radio amateur exam where it says… ‘use only enough power as is needed to maintain a contact’?  I guess not.

Looking out the shack window, I’m very surprised to see that the sky has turned a strange colour.  Being Scotland, it’s normally grey, but today is different, it’s a lovely shade of… umm… err… sky blue!  Once the missus is back from the shops with the ‘messages’ as grogeries are called in Scotland, I’m off to the park, with out rescue greyhound Cleo and a 2M/70Cms handy.   According to my missus, I’m addicted to those b**dy radios. I guess he just might be right.   But I like sunshine, long walks with the dog, taking photos with my digital SLR camera and …. gabbing on the radio. Heck! Did I just mention r**io again!  Hmmmm, maybe she’s right! 

Whats that weird droning noise?  OH, that’d be the PSK   Thats it! I’m off to the park!

73 AL GM1SXX

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