Norcim rc electronics club page 18……









Looking at the latest BMFA news I noticed a couple of 1970 adverts for Staveley  Control. Evidently they had recruited Doug Spreng to produce  digital system but were still offering an analogue proportional system designed by Mike Dench. Seeing the advert got me to thinking about the differences between the various systems and I concluded that only pcm could lay claim to being digital.

With regard to pcm., did anyone produce a fully digital system with shaft encoders on the sticks right through to digital servos? I get thoroughly confused because what is currently termed digital is in fact essentially analogue.

PCM is of course digital where it is applied but sticks and servos are definitely analogue in my book.




A few good snippets about Stavely. Yes 'digital' the word, was used from early days but you are right, it's really still analogue. Think when mark/space and different tones were used with old analogue voltage feedback servos suddenly changed to consecutive pulses being transmitted.....the word DIGITAL got in there somehow and it's stuck ever since. On a similar subject, just before FM came to the UK with 10KHz spacing. Micron had invested in the purchase of a spectrum analyzer to help with development.

Germany already had FM and Micron got hold of a Simprop system to see how it was done. Interesting bit was the AM transmitter Micron had at the time was as clean as the Simprop FM ! (sidebands 40db down at +/- 7.5KHz). It looked as though at least the Micron AM Tx would have been capable of working on 10KHz. Indeed, many early imported 35MHz were AM. Unfortunately FM receivers didn’t like working alongside an AM Tx (even many channels away) . In the end the 'new' FM systems won the day however and all the importers began to bring in only FM stuff. Strangely, micron's 'FM' receiver of that time used their conventional AM front end along with auto gain control. This front end fed its IF into a standard FM chip TBA120, via a 10KHz ceramic filter. Their standard 4015 or (4017) decoder followed. The result was an FM receiver that was totally deaf to any interference from AM TX's. At the first Sandown Park show where UK manufactures were showing their 'NEW' FM gear for the first time....only Skyleader and Micron had FM on display. Micron ran out of kits and took home many pre-paid orders for postal delivery.

Interesting that early UK FM radio control was introduced on the existing UK 27MHz band. (35MHz band came later). The 27MHz band was completely dominated with AM transmitters so any FM ‘newcomer system’ would have to be real  tolerant of the AM dominance. Micron got it right in those early days with their receiver design. I remember at early flying displays, Micron demonstrated their FM system flying very close to several active AM transmitters perched on a table in the middle of the flying site.




Just remembered 'ACOMS' first import to the UK for 35MHz was AM. Think a few imports of AM stuff came in before the problem of the two systems AM and FM not getting along together on the same band (except Micron which was happy with AM transmitters). I do remember a few meetings of traders/manufacturers at that time deciding that import of AM systems would stop, allowing all warehouse stock to be sold providing 'FM systems only' were then imported. I think there was another imported 35MHz AM system too. As far as I am aware, the UK allocation of the 35MHz band for flying models only……does not state ‘FM only’.

SLM tooled the special Rx case for the double deck Micron Rx. Strangely at a much later date when that Rx case was no longer used, Fleet paid Micron for the use of the Rx case as a TX/RX charger !!!! So Fleet's charger was originally Micron's first FM receiver.

How about that then !





Q.. Hi Terry… I remember the first dual proportional radios way back in the sixties. The servos for rudder and elevator ‘quivered’ a bit but they flew very well alongside the bang bang reed equipmentof the day. Have you any circuits of these early systems ?


David Boddington and Terry Tippett2Sorry Barrie, I’ve asked around but probably because those early pulse proportional systems were quickly followed by analogue feedback servos, they had a short life and not many circuits exist. 

The first dual proportional radio I tried was during the late 50s. It was the tail wagging system called Galloping Ghost. This worked quite well. A couple of years later I did try speeding up the pulsing of the transmitter so that the flapping effect of the servos was almost unseen. (This is probably what your talking about). The Tx joystick movement altered the pulse mark space which moved a spring centered servo proportionally left/right. Up down movement of the joystick altered the pulse rate. This was converted in the receiver to a second mark/space channel, controlling the elevator servo. This radio system looked real good and smooth compared to Galloping Ghost. Several electric motors and converted servos of that time were tried. The best results came from slightly converted Graupner Bellamatic 2 servos. These used expensive Siemens TO5 electric motors which were coreless. The pulsing direction change of the armature consumed less current. The Bellamatic2Bellamatic 2 servos used a scissor spring, to return them to center. This didn’t give proportional movement with the 80/20% mark space input. The scissor centering spring was replaced with a piano wire torsion spring which fastened to the outside of the servo body. This radio flew the model quite well but there was a second or two delay of the servos responding to the joystick. This looked OK on the ground but in the air, not so good and led to much over controlling. There was obviously a knack involved in flying this system which unfortunately I never found.

The picture attached shows the Fast Rate Dual Proportional system being demonstrated to Radio Modeler magazine columnist David Boddington (top of pic) The second picture shows the standard Bellamatic2 servo. The scissor centering spring can be clearly seen in the left hand servo, just below the output arm. Very easy to remove.




Q.. Hi Terry…looking at David Caudrey’s Page 9 and 9 part two of transmitter circuits, I notice that all the FM circuits use a varicap diode to produce the frequency modulation. I also have a Multiplex and a Simprop Tx which uses varicaps. How is it that the Micron FM transmitter (which I also have in mothballs!) is the only one that does not use varicaps for making FM ?


Good point Roy….way back in the last century, (probably early 70’s) Micron could see that FM systems would be the future of R/C (even on 27MHz as it was then). Several manufacturers in Germany and Lextronic in France were already using FM. With a couple of imported systems and other info it became clear that they all used Varicap diodes to produce the frequency modulation. Microns problem was…they produced kits of electronic parts to home build the transmitters and receivers. The varicap needed a trimpot to set the FM correctly. This needed an expensive Lab Digital Frequency Counter…..Ooooops ! not a lot of modelers had such a thing in thier knife and fork drawer. Micron commissioned a freelance RF expert called Mike Meakin to look into the problem. Mike eventually came up with a delightfully simple solution. He used a ‘slow’ switching transistor to simply switch in and out, a second capacitor in series with the plug-in Xtal. Once the values of the two capacitors were found accurately in Lab conditions, the kited transmitters would simply be CLONES of the Lab transmitter. This meant that Micron transmitter kits when home assembled worked correctly to spec without the need for electronic equipment of any kind. Many thousands of kits were sold over the next several years. Mike Meakin’s circuit cost Micron less than 10p per transmitter ! Micron’s circuit is unique and not one you will find in the typical RF textbook !





Q..Hello Terry…Nice website! I’ve been a member of several clubs in the UK over the past five years now but I have never once come across any home made radio ! Your website is full of home made Radio Control and circuits. looking at the visitor map, there is interest from modelers all over the World! Why is it that there are no home brewed systems to be seen here in the UK ? Do they exist at all here or in other parts of the World ?


Thanks Mark…the reason why you never see home brewed R/C gear here in the UK now or for that matter in most other countries, is called PROGRESS!. Sixty years ago ALL ! R/C modelers made their own radio gear. The model magazines of the day in the UK, France, Germany, United States, etc were all full of articles of how to build Radio Control systems. Thousands were built and enjoyed by model flyers. These articles were the seeds of inventiveness and often used in school science & technology.  Slowly but surely, the ‘Model Related Authorities’ began drawing up their own ‘Regulations’ and ‘Modifications of Regulations’. Often the members of these committees were not even R/C fliers.!


TODAY?…. if you are still part of the ‘Soldering Set’ and now took your home brewed R/C gear to the local flying club…then you would be told quite emphatically that you couldn’t use it. (Regulations!). If you turned up with your home brewed gear at an organized model flying event…you would not even get it through the gates! (Regulations!) The only place you can now fly home brewed R/C gear is a large unpopulated open space by yourself. Although, you would have to keep in mind a possible visit from an anti-terrorist squad claiming that you were using unlicensed transmitting equipment ! REGULATIONS have stifled freedom of inventiveness and R/C enjoyment here in the UK and the EU, Australia, USA, and beyond.

So you see Mark, it is unlikely that you will come across that lonely guy in a field somewhere, still flying his homebrew R/C gear. ‘Those that know better’, have put a stop to it !





(and relating to the email directly above)

The following is a nostalgic taste of typical model magazine adverts of yesteryear.

(compiled by David Caudrey)



Pecon RC advt2                           Micron Advt2


The two above adverts were printed in UK RCM+E magazine It shows that at that during the 1970s, kits of

 electronic parts to build your own radio gear were well a part of radio control modeling. The

Micron advert was as late as 1978.


Remcon RC Advt2     Teleradio RC Advt


Again the two above adverts printed in UK ‘Radio Modeller’ magazine dated 1970 show much interest

with home assembly of radio control systems.


Image (3)a        Microtrol RCa



Another two well recognized UK radio control systems of the early 1970s….again all in electronic kit form.

Kit manufacturers of this era were inspired by magazine articles and magazine series of ‘how to build a radio

 control systems’. Superb articles came from the UK, French, German and mainly US magazines. Other, strictly

 electronic magazines such as the ‘Elektor’ from the Netherlands had great influence too, although

the English version of the magazine only became available in 1975.




The above ‘Radio Modeller’ advert for Radio Control in Kit Form dated May 1986 shows that home assembly of radio controlstill kept going through the eighties and beyond ! Indeed MICRON still produced electronic kits for

EU ‘Type Approved’ 35MHz Radio control equipment until the year 2001 when the founders

retired and sold on the business.




Hi Terry and David

I have recently retired and dug out some of my old Micron Radio Control gear that I used in model boating days. Looking through your website I can’t find any reference to servo circuitry. Andy at Micron advises to use Futaba servos which I have coming in the post. With now time on my hands, I would like to revive my electronics interest and build a servo. Can you point me in the right direction to obtain a servo kit or even a servo amplifier circuit.


Sorry John W…….. We doubt whether you will find any radio control servo kits around now but we may be able to sort out a couple of servo circuits for you. Micron’s very early servo circuit was before Integrated Circuits came on the scene. It was however an interesting variant of an analogue servo circuit that they had used successfully in fast pulse proportional systems. An extra transistor (5 in all) at the input, produced a linear volt rise of the digital pulse. The analogue amplifier simply followed the peaks of the voltage rise. Fat pulses gave around 3v5 volts input to the analogue amp. Thin pulses gave around 1v5 input. The amp circuit was named by Micron as the ‘DACS’ amplifier. (Digital Analogue Conversion System). This simple circuit still needed the ‘old’ four wires to the servos, i.e. it needed a centre tap wire from the battery. One advantage however was that in the event of flying (or sailing) out of range, all servos returned to centre ! (a change of one resistor value produced a throttle servo ! It sent the servo to one end to kill the throttle).






I've been looking at your brilliant norcim website and wonder if you can help with some further information.

I've bought a 2nd hand JR3810 Tx that has 3 digital and 1 analogue trim control.

The Tx was mode 2, and I'm trying to convert to mode 1.

I've move the mechanicals to suit, but it appears that a previous owner had already been 'tinkering' with the wiring for the trim 'pots'. I was unable to test the Tx before buying - it is my 2nd 3810 and I'm rather a fan of these using Frsky 2.4 modules.

Do you have a wiring diagram for the sticks/trims so that I can re-wire to allow mode 1 use please.

Many thanks,



Hello Peter

Sorry but we don't know anything about the JR3810. I hope you manage to sort the thing out. We could do with some input to the site about the Frsky 2.4 Gig modules you are using. Do you find them OK for range? Any pictures would be great.

Cheers Terry and Dave.


Hi Terry,

Thanks for the email.

I had been using a plug-in Frsky module in my original JR3810 tx for some time until the module pins became loose causing a radio failure. The 3810 was quite old (2nd hand) so I hard wired in the Frsky "hack" module, and since then had no further problems. This also had the benefit of replacing the 35MHz antenna with the 2.4 item.

I have also built a single channel transmitter using Phil G's encoder module and attach a couple of photos of this complete with Sharkface. This operates the rudder servo as a bang-bang (as per Elmic Conquest escapement) control which was how I flew my original Sharkface in the 60s - photo attached. Both Frsky units have excellent range and bind on switch-on faster than my Spektrum DX7.

Single channel Tx (1)a         Single channel Tx (2)a           Sharkface2


I am also using JR3810s with the FRsky 2.4 modules. This module requires the Tx to be set to the standard PPM coding. I have two JR3810s, one has the plug-in RF module shown below, left, the other I have hard wired the FRsky "Hack" module; (shown on the right hand side) the latter being an older Tx with not such secure plug-in module retention, hence the "fix".

 JR Module2

FrSky 2I'm using the FRsky 8VFR and 8VFR HV-2 receivers, also the small FRsky 4 channel receivers (without range issues). All work fine.

Best Regards,



Hi Peter

Some good stuff that you are doing! good to hear the 2.4G conversions are working so well and thanks for your emails. We traced a supply of the FrSky plug-in JR 2.4G module shown left to

priced at £11.67 .....and the DIY version shown right can be found at for just £12.99.



Peter Gascoine shows just how cost effective it can be to convert your favorite computer Transmitter, or indeed a favorite elderly vintage Transmitter to the new well established radio control frequency band. Thanks Peter !











Hi Terry,

FRsky set up (2)Please see attached photo of the FRSky system installed in one of my models.The model is a small pylon racer with an OS25 FX up front. It goes well!
I have been totally satisfied with 2.4GHz, so much so that I sold all my 35MHz gear and converted first to Spektrum (which I thoroughly recommend and praise Horizon Hobbies for such a fantastic after sales service) that I still use and more latterly to FRSky with the JR3810 Tx. The greatest benefit is the security knowing that nobody can shoot you down. I started way back with single channel using 27MHz regen equipment so I really appreciate this! The FRSky system has a faster link on switch-on, and also has the benefit of only requiring one Rx as opposed to the AR7000 Spektrum having the satellite Rx. But having said that, both systems work perfectly well and show a significant improvement over 35MHz when flying electric powered models - there are no glitches at all. I normally try to place the ends of the small aerials outside the model, but they seem to function perfectly well inside the fuselage which can be a benefit.

I belong to 2 model clubs, the first has many old boy members with a large 35MHz contingent, the second has more new (not younger!) members who have obviously started with2.4MHz.
With the FRSky equipment so reasonably priced, I can see no reason not to change and benefit from this added security.





HI Terry

Turbulent and Toucan 005aSeeing your paragraph on early servos with four wires and their self centering in absence of a signal brought home to me a recent happening. Desperate for something to make quickly, I purchased  a West Wings Toucan kit.

It is an excellent kit of accurately cnc machined parts for a small shoulder wing model slightly reminiscent of the Shorts Toucano. Being a small model intended for use with a 300 size motor, it dispenses with an undercarriage.

Preferring models to rog. I decided to fit an undercart and to power it with the optional 400 size motor. Because such a small model would not be flown at distance I fitted a 35MHz micro receiver.  So modified, the model was very twitchy to fly; having a marked tendency to stall on the landing approach. To overcome this I built a new wing with 25% more area and a higher aspect ratio. For some reason I concluded initially that this hadn’t improved matters and put the model to one side. Fancying a challenge a couple of weeks back I resurrected the model and I was pleasantly surprised to find that it actually flies beautifully. However my euphoria didn’t last because, during a low pass, it suddenly dived into a wheat crop.

When recovered, model was not damaged superficially but nothing worked. On investigation I found that the micro servos had  apparently gone crazy due to loss of signal, completely mangling the control linkages. Obviously micro receivers do not fail safe in absence of a signal. A 2.4 Ghz receiver with failsafe is now installed.




Hi David

Good to hear the Toucan is now ‘tamed’ and flying great. Looks really good too and as you say, there is a ‘Shorts Toucano’ in there and wanting to come out. It is a shame that we have no detail circuit of the early DACS servos that flicked to center with loss of signal. Must be fifty years ago now that these simple transistor voltage feedback servos were used. Amazing that they did offer such a simple self centering effect with loss of signal !







Skyleader potsDon't know whether you guys can help or you can pass me on to someone who can.

I have recently got out of my loft a Skyleader SLX Proportional R/C 4 Channel 27Mhz set that I used to fly various models such as Wot4's, Ripmax Dazzlers etc.

It has languished in my loft along with my planes and another set of Skyleader Clubman 35Mhz gear for more years than I care to remember.

I have set about refurbishing the 27Mhz set so that it can be used in cars or boats. As expected the Nicads had corroded and there was also the dreaded "black wire corrosion". Having managed to sort out the latter and source some new batteries for receiver and transmitter,  when first fired up I was pleasantly surprised to find the servos responding. However I have now found that corrosion from the transmitter battery has spread to at least a couple of the components that I believe are called trimmer resistors that are mounted on the PCB. There are two of these per channel and I want to replace at least one pair of these as the servo on that channel rotates constantly and the corrosion appears to have badly affected the carbon tracks on the trimmers.

The problem I have is that I need to establish the values of these trimmers so that I can source some replacements. The only markings I can see are paint spots  that look like Yellow, Mauve and Brown on 4 of the trimmers and two Blue spots (or no markings) on some of the others.  Obviously these trimmers need to be of the correct value and the set will need to be lined up when they are replaced. I have attached some photos of the rear and front of the PCB (which is marked SKYLEADER T2103) and also of the main case.

I note that on the site there is a circuit schematic for a Skyleader Courier 35Mhz Xmtr, but this does not assist in this case.

Any help would be much appreciated!!

Best Regards


Hi Andrew

Thanks for your email. David is looking through his notes to see what he can come up with.

The pictures you sent are clear and we can see the problem. I am wondering if you could use a de-solder tool to carefully remove a 'good' trim-pot to measure its value. ?

Anyway I will get back to you soon.

Regards to you and yours



Hi Terry


Well after a bit of a struggle I removed two pots from a known good channel. Not too easy as the corrosion has affected the PCB and so the tracks tend to lift from the board when de-soldered and when the components are put back. So had to bridge a couple of connections on the board with wire. Fortunately when put back the channel still works OK!!

OK so when I measured across the carbon track (two front legs) of each pot as you suggested, on one I got a measurement of approx 500 ohms and doing the same on the other pot I seem to get approx 5K ohms. Now I don't know if these values are in line with what would be expected. Would yourself or David happen to know if these figures are in the ballpark?  If they seem to be OK then I would replace all channel trimmers with pots of these values as they are so cheap to buy. Could you possibly let us know your/David’s thoughts on these values?

Once again many thanks for your help with this.

Best Wishes



Hi Andy

Talking to David suggests you are on the right lines removing the trim pots and measuring. The values sound correct. When you replace these, try to position the wiper by eye as best you can to the position of the one removed. This should give a 'working ' position for that channel. One of the new pre-sets may need a tweak to get the servo to center on that channel. 


Hi Terry

Said that I'd let you know how I got on changing the trim pots in my old 27Mhz Skyleader transmitter. After a bit of a battle finally got the two corroded ones done. The reason for the struggle was because the PCB tracks kept lifting because they had been badly affected by corrosion from the old NiCads. I had to use wire straps in places to replace tracks that had lifted/disintegrated. However eventually got the pots changed and then threw myself an enormous wobbler over the aileron channel which didn't work intermittently. After much head scratching, checking work done etc, eventually discovered it was the servo on that channel that was intermittent, nothing to do with the transmitter or receiver. Haven't looked at that yet, but think it is probably to do with the lead or plug having a dry joint or disconnection somewhere.


I do have one further problem with the transmitter however. The pot on the rudder channel is very noisy and causes other channels to twitch when the rudder is used. The pots used in the Xmtr are made by Bourns and are 5K linear variable ones with solder tag connections and a shaft with a flat. I have searched as much as I can for a replacement, but have not been able to find a direct replacement.




Hi Andrew

Good to hear from you. Think the bourns pots you have may be plastic film type. If there is a 'way in' to the pot track (even by drilling a tiny hole) it would be worth a try at a quick squirt of WD40 into the pot housing. Pad the inside of the Tx with kitchen towel to catch inevitable splashes. Martin at SLM engineers may have some 5K Bourns pots left over from R/C days. They may not be the exact type but definitely 5K. Worth a try. I think these pots were only imported by R/C manufacturers of the time and not a stock item of the likes of RS, Farnell, etc.


AndrewBurrageBipeHi Terry

Thought I'd let you see the results of the first refurb of my collection that have been in the loft for 15 years plus.

Its called "The Basic Bipe" and is built from a plan in the American "Radio Control Modeller" magazine of March 1977.

I previously flew this with an OS40 and my old set of Skyleader 27Mhz that you helped me repair recently. It has now got an Enya 40 up front, nothing to write home about but a good old slogger that I managed to get from "fleabay" along with another exactly the same. As you will see from the photos I will now use my 35Mhz Skyleader Clubman rig which appears to work perfectly after renewing the batteries and clearing up the black wire corrosion. As for the bipe itself I managed to just repaint the fuselage and tailplane, but had to strip the nylon covering off of both wings as the paint I had used previously had crazed and cracked. Rather than spend a lot of time and money recovering and respraying the wings when I still need to prove that the R/C gear is OK I opted to use Easycote as a quick and easy cover job and that accounts for the colour difference between the wings, ailerons and tail. I really do not like this type of heat film covering and would always usually opt for nylon and dope as it adds a lot of strength and you can choose your own colours!!


Regards Andrew






Good morning from NZ,

I have been reading your Norcim site for a while now, and have been meaning to write, but I see that you have recently added some more pages, and that has sparked this.  This covers a variety of topics all in one email;

Firstly, I bought a PL-7D transmitter kit from you, around Aug 1977, that gave some years of good service. I was at the RAF College in Cranwell, Lincs, at the time.

I see that Dave McQue is now "late" I never met him, but often read his material, as far back as in the old (small size) RCM&E. He will be missed.

It has been interesting following your comments on various versions of FM receivers and their early problems.  I think (?) all this started with Terry Platt's series that was published in mid-79 in RCME&E. It was interesting to read his comment in the first issue that went something like::  "The very best receiver used a passive DBM, but at the last moment Motorola introduced a great IC for RC that was almost impossible to ignore"  

I guess that he did not do a lot of testing after finding the MC3357, as the wide-open front end, a FET pre-amp and internal mixer weaknesses soon manifested themselves with 3rd order IMD and cross-modulation off AM sets. I, and several others, did some work-arounds to reduce the problem, usually by converting the FET into a mixer of some sort.

I see that others had different solutions, Micron used a starved-current mixer and Fleet used a FET mixer with a tiny amount of LO coupling.

In the USA, Mike Dorfler did several versions, but used cross-coupled FETs and front-end AGC.  Fred Marks did an excellent version with a Mini-Circuits DBM. While others (mainly in Europe) went the Siemens SO42P way.

All this is largely now superseded by SS systems on 2,4GHz. However, we here in NZ are starting to see the odd problem as the noise floor creeps up, especially in urban areas.  We operate under a GURL (General User Radio License) that allows the band to be pretty much a free-for all.  Up to 4 W EIRP is allowed and the terms of the license are very clear:   ie  You have no special rights, it's a shared band, interference is just tough luck, and don't even think about complaining  (which some RC modelers are !!)

The marketing weenies have been playing silly games by claiming that such systems are "impossible to interfere with"  This is nonsense, as everything has it's limits.  Allowing for the process gain  (10 log chipping rate/data rate) and a few more dB for luck, suggests that most systems will collapse with about 10-100 Watts from an interfering emitter. That is quite true. I have a quite old high power signal source, the Philco-Sierra 470 that can put out about 50W between 2 and 2.6 GHz, the US military used to use these for EMV/EMI/EMC/ testing years ago-that's how I acquired this one, I was a contractor working with them at NAS Patuxent River doing some avionics testing.

And yes. this does collapse most systems, instantly !

It can be argued that this is not a "real" or "fair" test. But it can be. Here in NZ, Hams can now operate with up to 1000W in most bands (inc 2.396 to 2.45 GHz) and can also use a high gain antenna, the DL6WU or G3JVL Yagis, being popular and easy to make, with about 18-22dB of gain. So the field strength can be very high indeed.  The most usual application they experiment with is EME bounce comms where the high EIRP is important. I'm not sure what the regulations are in the UK.  Could you have the same problem there?

The mention of super-regen receivers bought back a lot of "interesting" and challenging times in the early 60's. Are you aware of a fascinating (and now very rare) book by a JR Whitehead of the TRE, (Cambridge University Press, 1950) ?  It deals with the theory nicely, as well as providing good schematics and descriptions of the British wartime IFF transponder, and the German Lichtenstein Radar receiver. It also has a small section on very simple "soft" valve (Raytheon RK-62) receiver "used for radio-controlled model ships and aircraft" !

Lastly, I read the comments on anodizing with interest. I have had limited success with this, However, there was a very good article in "Model Engineers Workshop", Oct 2012, issue, where a Ramon Wilson claims to have solved most problems. Part of his success was by using a Titanium wire electrode (a TIG welding rod) to connect to the article in the tank.  He has also found that old-fashioned ink does a great job of colouring. Parker Green and Red  and  Watermans "South Seas Blue" being very good.

I would agree that the new Dylon dyes (in the plastic sachets) are useless for this purpose. I read somewhere that Dylon had a fire in the factory a few years ago, and when they re-built, they changed the formulation, partly to meet some EU regulation over hazardous substances !?  Anyway, none of it works !  I have had some good success with RIT dyes from the USA, but not all colours work. (Sunshine Yellow and Scarlet are good)  I have also read in a forum that some inkjet printer dyes work well, but have not tried these yet.

I could easily obtain the correct anodizing dyes, but the suppliers will only sell them in a 1kg packet for around NZD400 !  That's far too costly, and would be enough for several lifetimes !

All the best, and keep up the good work.

Barry Lennox


Hi Barry

Good to hear from you and of course NZ. ! Barry, I can tell from your mail that you have lived R/C for, should we say…enough years to know a bit about it. (let’s face it, how many flyers remember the ‘Small RCM+E magazine’ ! ).


I have highlighted the bit of your text that I find most interesting and technically very well explained ! You make a particularly good argument for not using the 2.4 Gigahertz band for Radio Control in NZ. In fact I recon your thinking may well apply to many other parts of the world too.


I have just deleted the text I had written here simply because after reading it back…..I recon I was simply re-writing and agreeing with everything you outline above !


I hope a few people read your comments and let us know how they have been getting along with the 2.4 Gig shared radio band. Any comments, good or bad, will be greatly appreciated…. Have any of you Guys actually returned to 35MHz ? ?.....let’s know what happened !




Many Thanks Barry.




Hi Terry

Having seen Barry’s e-mail in Page 18, I begin to realise its full implications. Although not versed in the subject, I have always been skeptical about the claims for spread spectrum operation in an ‘open’ band; fearing that an increasing noise floor might eventually cause range issues. If I understand it correctly, Barry’s ‘10 log chipping rate/ data rate’ is the effective signal to noise ratio for spread spectrum operation (akin to - ∆f / fm for frequency modulation). If so, it is interesting that the Futaba 6EX 2.4 GHz I use sends its data at twice the rate of the 35MHz transmitters. This caused problems with some of the installed electronic speed controllers (ESCs) when 35MHz receivers were replaced by 2.4 GHz receivers in my most frequently flown models and was the reason for the in-line ‘data rate halving circuit’ in Page 10.




Thanks David (David Caudrey is Technical Co-Author of Norcim). Any of you guys with a Futaba 2.4 Gig transmitter….Page 10 will be of interest for ESC compatibility.





Hi Terry,

Like the NZ Guy, I’m not entirely convinced that 2.4ghz will be OK in the long run.  What started me on this train of thought, and what persuaded me to get a 2.4ghz speccy analyzer, was that I seemed to be shot down on this band about 12 months ago. First, the circumstances:-

I fly (sometimes) at a very isolated site here in Spain, and when I arrived there was just me, and another flyer who was several hundred yards away, fiddling with his model on the ground.

I prepped my little leccy heli, hovered it for a few seconds, all was well so I added power and a bit of forward stick, and the heli commenced a climb out up and away into what would have been a normal climb-out. After only about 75 feet (I can estimate this distance fairly accurately, as I fly control-line sometimes, on 70 foot lines, aren’t I sad?), it started to dive and continued straight into the ground with me having full back stick on all the way to impact. I was a bit pissed off to say the least.  A few minutes later, having picked up all the bits, and disconnected the brushless motor wires, I powered up the heli, and everything worked just fine!! I then wandered over to the distant flyer, and noted he was fiddling with an FPV model (this might have been significant). (FPV…First Person View or Video….)

Shortly after this, I went back to the UK, took the 2.4ghz gear with me, and flew it many times in a slope soarer, with others on the slope, so the radio was ok!!!

Then I got the speccy analyser.....and noted this cheap Hong Kong 2.4 set only transmitted on one narrowish band of frequencies in the 100mhz wide band, unlike Spectrum DSM2 (which I now fly) which transmits on TWO wider segments of the band.

Then I thought...what if the FPV model was transmitting its downlink video in the 2.4ghz band? Such a powerful (broadband) signal might just be right on top of my transmission...the result of which would be my loss of the data link from my Tx to the model at some point!!!

So that’s my hypothesis.....I think that FPV model shot me down.

How could it have been avoided?  Well, with that cheap set, no way, if he was transmitting on top of my signal. BUT a Spektrum DSM"2 would have been ok (which is what I now use), but any of the latest Spectrum DSMX sets, or any Futaba 2.4ghz sets are immune as they use proper spread spectrum transmissions across the WHOLE band.....a serious improvement.

Incidentally, I remember when 2.4ghz was first on the market, and one of its selling features was said that it would look for a quiet part of the band, and use that.  I have looked at MANY 2.4ghz sets now, and can say with confidence that NONE of them exhibit that characteristic. Some slightly better simple sets MOVE their frequency band every time you switch them on, and Spektrum DSM2 MOVES its two bands of frequencies again, every time you switch them on, BUT its the same movement every time you switch the gear on, i.e. it takes no account of other signals on the band.

Now onto another comment....I have been using the speccy analyser here in Spain a fair bit, and the band is getting busier by the week, and some of the signals are STRONG (and this is not only at our flying site, but actually ANYWHERE) and at 10dB below one milliwatt (received), that’s one hell of a strong signal. They are there quite often, and that’s worrying! Spain has no spectrum policemen, so ANYONE can start transmitting, and it seems that they are!




Wow ! Michael…. That is one hell of a story and thanks for the technical groundwork and expertise you have put into tracking down the problem. A bit scary really that just one extra user of the 2.4 Gigerhertz band appears to have caused a complete wipeout of the helicopter. When you consider that there are Millions of transmissions every day and night on the shared 2.4 Gigahertz radio band (world wide) (and these are not R/C transmissions!)  it is not surprising that that some things go wrong. Your findings above will help future modelers.


Terry T







DC1Built from an original Mercury free flight kit for 0.5 diesel power !

David has used electric drive in this version. Some registration markings have now been added and further detail of the electrified version will be added here later. Not flown yet but first flight notes will come soon.

David has added a registration in memory of the late Canon Michael Benton who sent the kit to him when he realised that he would never be able to build it.

Hopefully it will fly close to where Canon Michael Benton can participate in its progress.



















ODgliderAn all balsa design with split wing for carting to the field. Looks a pretty model with wing area well capable of catching a thermal or two. Flying characteristics will be added here later.
























The receiver looks like one of the ‘standard’ type versions available in the seventies/early eighties. Sold in electronic component kit form for R/C modelers to assemble themselves ! WOW…you just don’t know what modelers got up to in those days. The speed controller was based around a quirk of a standard MC4001 Cmos integrated circuit. (Micron could get these at the time, in quantity, for less than 10p…but don’t tell anybody !). The electric motor was a standard  ‘Sun’ 540 size industrial motor which came from Micron with a diode and capacitor (and a micron sticker) in the pack to solder across the input terminals. These components very effectively suppressed the flight motor interference to the close by receiver. The motor was not intended for electric flight of model aircraft. In fact it was a motor for industrial use such as car side window operation. By loading the motor with a fairly hefty prop, diameter and pitch (usually Graupner type) the motor produced fine electric flying for glider type models. Many of these motors have lasted for years, not only in cars but also in micron model gliders.


The micron speed controller circuit









INDOOR AERIALS ! Barry Lennox was chatting recently about the long flex aerials of 27, 35, 40 MHz receivers. He outlined a method that he has used to make these things unsightly.

Indoor AerialI did some range testing yesterday at a friends place, with the receiver held about waist height, and the transmitter likewise, with just section of antenna up (OAL= 13cm) we obtained 260 metres before the servo started to jitter. 


 ‘’ One of the criticisms of the 2.4 GHz bunch is the "silly long aerials"  so I used an old technique, to compress up the Rx antenna. I wound it into a loose helix about 4 cm across and 25 cm long, small enough to fit in any model. (See attached pic) Then the range dropped to about 190 metres, still very good.’’


For a small model I would wind it on a bit of card, balsa or (being cheap) a bit of old meat tray. There's actually quite a bit of info published on shortening and short antennas.  My main ref is the various papers published by the R&D branches of the US military, obviously, they would like antennas to be as small as possible, and preferably invisible and weightless! One Dr Steven R Best (he was a consultant to the USAF for a while) has published some excellent info. He does make the point that much of his work was derived empirically  (aka cut'n'try !) Helical antennas

I'd agree with Dave McQue, our antennas at VHF are pretty lousy. There is a formula that allows one to calculate the impedance of short antennas and it's reasonably accurate. Yes, just a few pf and very little R.  I'll do some calculations and measurements to verify that theory and practice agree.


For several years, I made normal-mode helical antennas for transmitters (pics attached) They had a small loss compared with the usual telescopic ones, but it was very small, and insignificant compared with all the other variables in the Tx-model path loss. Their main problem was they are a very high-Q tuned circuit and thus very narrow band. Harrington and Chu did a lot of work on small antennas and their bandwidth trade-offs many years ago, their papers are worth reading, but a bit heavy going- it's much much easier to cut'n'try !


They were also a bit of a b------ to manufacture as the PVC sleeve and little end cap, all detuned them by a small amount, so you had to allow for that when winding the antenna. It was "resistant to calculations" and the exact amount of detuning was learnt by trial and error, then experience.








JUST BEFORE MICRON (UK) CEASED PRODUCTION OF THEIR TRANSMITTERS YEAR 2000….their transmitter aerials were in fact the shortest of the 35MHz and 40MHz types at just 67cms total length. For some reason these aerials gave equivalent field strength readings compared to the internal base loaded 110cms standard at that time. The shorter length made it easier to move about on the pilot line without poking fellow pilots eyes out ! An added feature of the tuned coil design was a Pi-L coil effect which further filtered out of band harmonics and spurious transmissions. The telescopic aerial was based on a Maplin import and modified to the spec shown at the side. The coil had a red heat shrink tube sleeve over it and looked quite ‘Cool’….



















Hello Terry,


I have really enjoyed reading your web pages on some of the early 27MHz and 35MHz receiver designs. 


I have tried to understand how the designs work and why the design choices were made.  One of the questions that has come up in my mind is in relation to the typical xtal oscillator circuits used in the early receivers (eg Micron Superhet or Dorfler).  These are specified as 3rd overtone oscillators, but I’m not sure I understand how the fundamental is suppressed. 


I’m writing in the hope that you can shed some light on this.  I have had a go at understanding the circuit, but have not been able to locate any literature describing it.


My best guess is that the oscillators are effectively a Pierce design with phase shift being provided by the transistor output impedance driving into the collector-emitter capacitor and further phase shift by the transistors base/miller capacitance.  In the AC small signal model the RFC (from collector to supply) in series with the emitter resistor appear in parallel with the collector-emitter capacitor forming a low-Q parallel LCR circuit.  I assume that this LCR circuit is simply tuned to resonate between the fundamental and the 3rd overtone to provide inductive loading at the fundamental and capacitive loading at the resonant frequency.  Does this seem in the ball-park?


I would really appreciate any help you can give me in understanding this circuit. 


Thanks again for your fantastic web site.



Hans Trinkle.


Hello Hans

Many thanks for your email.

I think that you are ‘well in the ball park’ with your description of the simple crystal oscillators used in 27 to 72MHz R/C receiver designs but I will join in with some notes for Xtal Oscreaders. Most of the R/C oscillators are based on a single stage transistor amplifier like Fig 1. Often the oscillator circuit would be minimized (component wise) to that shown in Fig 2. Mike Dorfler was perhaps the first to do this.


You are right that the emitter resistor in Fig2 does have a damping effect on the collector tuned circuit but in the receiver this is no disadvantage as a ‘rampant’ local oscillator just 455KHz away from the incoming signal somehow gets into the weak filtered aerial system at range causing problems. In Fig 2 the RFC would be around 10 uH for 27/35/MHz but more important would be the self resonant frequency of the choke used. This ‘self resonantFig 2frequency varies from manufacturer to manufacturer so it would seem more important to select an RFC for the  Self Resonant frequency of the Rx crystal used. Micron receivers (based on Dorfler and other designs) used a slightly different approach. To further dampen the receiver local oscillator (to allow a weak signal through from the Tx) they used a tiny ferrite bead in place of the RFC in Fig 2. This seemed to absorb oscillator activity further without reducing correct ‘Third Overtone’ frequency at startup and very low voltages. The 2.5 turn ECW on the FX1115 ferrite bead, gave just enough inductance to encourage the Xtal to ‘ring’ on its ‘Third Overtone’ but not nearly enough to get it to try oscillating on its Fundamental ! ‘Fundamental’ frequency crystals could have been used for receiver Xtals but their actual frequency is quite dependent upon the external circuit. The manufacture of Fundamental Xtals approaching 30MHz make them extremely fragile, they would not survive a fall of a few feet and would not be tolerant of engine vibration. This is perhaps why most R/C transmitters 27 to 72MHz use ‘half frequency’ (or third frequency) fundamental crystals and the Tx circuit doubles (triples) up to transmit. ‘Third Overtone’ crystals will operate on their fundamental frequency (9MHz for a third overtone 27MHz crystal) if forced to by the external circuit. But they are manufactured and ‘cut’ to favor their ‘third overtone’.



Crystal 2<FIG 3 shows the operation of a quartz crystal. Unlike a simple capacitor, the voltage swing of each terminal is the opposite of the other. This is similar to a ‘Pi Network’ talked about in Page 14 . Compared to a Pi network capacitor/coil arrangement, which has a selectivity ‘goodness’ of around 100 (referred to as ‘Q’), the typical quartz crystal can have a ‘goodness’ value (Q) approaching a million ! So the plug-in crystals that we use in our transmitters and receivers, keep the channel frequency extremely accurate.

Just a couple of thoughts about crystals. (1) they change frequency a little (very small amount) with age so after several years (say seven) they should be replaced. (2) the small can of the plug-in crystal is pressurized during manufacture to keep out normal atmospheric contaminants that would oxidize the quartz wafer. The crystal socket design and our ‘handfistedness’ in plugging the crystals in, leads to a weakening of the pins sealing at the base of the crystal. This allows atmosphere in and rapid decline of the frequency stability. (3) don’t be shocked by the fact that if a crystal falls from the bench onto a hard surface and it refuses to work anymore ! Inside the small metal can there is a wafer of desperately thin disc of Quartz and it will have shattered. Always have carpet under your bench.



Disclaimer: Note that the above email answers are those of the Norcim webmaster, Terry Tippett. They are not necessarily the views of any contributors to the Norcim wesite.




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