TX history of frequencies and modes

[Gary Morton]

Hello all, first posting, noob here!

My interest in RC comes from when I was a child and I used to visit the local model shop in York (early to mid 70's). My interest is actually in electronics and not the actual model flying, in fact I have never operated a RC model. I wasn't able to afford anything as a kkid , but things are different now .

Back in the 70's RCM&E used to publish electronic schematics of radio control TX and RX. I used to browse the magazine to have a quick look. These circuits have always fascinated me and I do actually have a few books. I also have some of the R.H.Warring books I used to get out of my local library back in the day.

Back in the 70's I tried to build a 5 channel "Microtrol"7MHz AM TX and RX, but it was a complete failure, because I didn't have the knowledge or tools to diagnose. Now I am retired I fancy building some RC electronics and putting them in a model of some kind. Sadly I didn't keep the home made PCB, but I did keep the tiny RX, which I tested a few years ago only to find out instead of using a NPN transistor I used a PNP. No wonder it never worked!

My question is about change in legal frequencies. Back then equipment was 27MHz AM. I have found a website which was helpful. I see that 27MHz can still be used (albeit not for aircraft), but there is now 35MHz, 40MHz and UHF.

Out of interest when did these new frequencies become legal/appear? For each frequency which mode (AM or FM) is allowed and/or preferred. Note: I'm not interested in UHF.

Did RCM&E every publish any designs for 35MHz or 40MHz?

I'd like to find a suitable design in order to build my own TX and RX, visit the local model shop (now Huntingdonshire) to buy a model plane, and next year I will find a local club to learn how to fly.

Many thanks for any answers.

[Gary Manuel]

Welcome Gary.

It would be nice to see some threads that put the E back into RCM&E. I don't have much working knowledge of radio electronics but would follow your quest with interest. Hopefully, someone will be along soon to help.

[Alan Gorham_]

40MHz is only legal for surface vehicles in the UK, not aircraft.

35MHz was allocated for model aircraft due to the rise in Citizens Band radio users illegally operating on the channels allocated for model use. Rather than police that we were given the new band. IIRC it was very late 70s or more like early 80s that 35MHz came in.

I know that 27MHz was still perfectly legal for model use but was discouraged in favour of modern, narrowband equipment. I haven't looked for a few years, but are you sure that 27MHz is now illegal?

RCM&E did publish designs for a 35MHz system but you might struggle to build them due to component obsolescence.

[Frank Skilbeck]

OK don't know the exact dates, but I got me first RC set a Futaba 27 MHz FM set at the start of 1980 and then a set of Fleet 35 MHz gear in 81/82, I think 35 MHZ became legal in the spring of 1980, and if I recall there was one manufacturer who offered a 35 MHz AM set, but by the FM was the way to go.

27 MHz can be used for all models, aircraft and surface vehicles, 35 MHz is for aircraft only and 40 MHz for surface vehicles.

Some info on early proportional transmitters here, including a picture of the RCME kit transmitter and Micron kit transmitters also.

I'm sure others with more knowledge than me will chip in soon.

[Peter Christy]

Welcome to the forum, Gary!

Wow! There's enough questions there to fill a book with answers!

A few quickies to start with. 27 Mhz remains legal, and as CB radio has all but died out, remains a viable option in many areas - but probably not near motorways! You can use AM or FM on 27 MHz.

35 MHz is FM only, and restricted to aircraft use. Similarly, 40 MHz is FM only, but for surface models. 459 MHz is AM or FM, but the only commercial equipment ever made available was all FM.

The VHF and UHF bands have all but been abandoned in favour of 2.4 GHz spread spectrum equipment. Nearly all currently available equipment operates on this band.

There were plenty of construction articles and kits for 35 MHz FM gear back in the day, but you would have to trawl through the haunted archives of RCM&E to find them!

If you like to tinker, something that might appeal is the growing "retro" movement, where people convert obsolete equipment to 2.4 GHz, either using commercially available modules or programming their own. There are also several encoders available using either Arduino or similar boards.

I would suggest you have a look here for some inspiration: singlechannel.co.uk

where you will find circuit diagrams and examples of equipment converted. There is also an associated forum at mode-zero

where you will find a bunch of people recreating / restoring / rebuilding older radio gear.

You may also find this site of interest: norcim

which contains lots of useful information and circuit diagrams!

Reading that lot should keep you occupied for a bit!

--

Pete

[Nick Cripps]

Hi Gary, welcome to the forum.

Section 24 of the BMFA Handbook gives a list of legal frequencies for model use in the UK.

[John Wagg]

As far as I am aware 27MHz is still legal to fly aircraft but I wouldn't recommend it. RCME published a design for home builders of which I have just scrapped mine after being in a cupboard for 20 odd years. The design culminated in 35MHz FM but is no longer available. Again it is still legal to fly and quite a few people still do. Building your own was a less expensive way of getting into RC.

Today's radios are generally 2.4 GHz and I don't know of any published DIY designs and probably not worth it.

2.4 GHz modules are available for converting some 35MHz sets to work with current 2.4 receivers but you need to check on their legality for using in the UK.

All above posted while I was putting ink to paper.

Edited By John Wagg on 10/12/2020 14:26:24

[J D 8]

There was a nice article about Fleet control systems in the September 2019 RCME.

For more info go to "magazineexchange.co.uk " It is possible to look up many old articles and down load for a cost. Some times hard copy's are available as well

[Gary Morton]

Posted by Nick Cripps on 10/12/2020 14:19:28:

Hi Gary, welcome to the forum.

Section 24 of the BMFA Handbook gives a list of legal frequencies for model use in the UK.

Thank you. Found it using google. I also found some other web pages which has given me a clearer picture. For some reason I assumed that 27MHz had been "discontinued", so was almost surprised to see that it still can be used, although I read that some clubs do not allow it for airplane use, due to possible interference I suspect.

[Gary Morton]

Thank you everybody for the warm welcome!

Thank you Peter for the multiple links (I will be sure to check them out), and the clarification of AM/FM.

Since my interest was back in the 70's when I loaned books from the local library, I still have an interest in vintage equipment, and I see that there are parts of the forum dedicated to that, so I will browse further. I recently spent a few hours viewing YouTube videos of vintage RC electronics, and it has sparked a new interest .

I recently spoke to a friend, who has a friend who has lots of back issues of RCM&E (nowhere near me). He is going to see if he can borrow some to scan articles of interest for me. If anyone could provide any specific dates of any TX/RX projects it would be most appreciated. I could pass this information to my friend to obtain the right issues.

[Alan Gorham_]

I must admit that when I recalled earlier that RCM&E published a design for a 35MHz FM set, I was actually remembering the RM Digicon set published in Radio Modeller magazine in January and February 1986.

The January issue is listed for sale here:

**LINK**

But the February issue might be worth scanning ebay for...

[Nick Cripps]

RCM&E did publish a design for a 35MHz set in a 4-part series in the May-August 1979 issues. The radio was designed by Terry Platt and several companies offered kits based on the design at the time.

A later issue stated that despite printing 48000 copies of the May and June issues they achieved a sell-out!

Gary, I've managed to scan the relevant pages so if you'd like to send me a PM with your email address (don't publish it on the thread!) then then I'll forward them to you.

[John Wagg]

DIY:-

https://www.youtube.com/watch?v=pjBnFZGfsjI&feature=youtu.be

[Robert Harris 1]

Many years ago I built a rx from a kit by Micron radio. they supplied all the components and pcb, you then had to solder the resistors etc onto the pcb. It used futaba crystals.It was quite successful,as I had a futaba tx..

[Gary Morton]

Posted by John Wagg on 10/12/2020 20:50:39:

DIY:-

https://www.youtube.com/watch?v=pjBnFZGfsjI&feature=youtu.be

Yes. Fascinating. I saw this very recently. Until I viewed it, I was unaware that radio control had moved to the UHF band. I thought that the way he made the case was very clever. I didn't know that this material even existed.

I want to go old school to begin with (i.e. transistor encoder), however at some future time I will use an arduino to read the pots and generate the modulation waveform. I also want to go old school and construct the radio frequency parts of the TX and RX, as they are a bit of a challenge. As a kid 27MHz seemed a really high frequency, nowadays its well in the bandwidth of most low cost scopes.

I've now ordered to RC gimbols(?)/joysticks from AliExpress. Thanks to interest by makers and robotics fans, the price of servos now really low and I have already bought a couple, although I have yet to use them.

BTW, general question, if I were to post pictures and information on my own TX and RX, would that be on-topic for this forum, and if so under which catagory should I post?

Thanks again.

[Gary Manuel]

Why not just post it here Gary?

Anyone interested in this sort of stuff would surely be interested in your history. There's always the option of asking a moderator to change your thread title if it becomes necessary.

Edited By Gary Manuel on 10/12/2020 22:14:32

[Bob Cotsford]

Was the Microtrol the homebrew that used a massive PCB filling most of the back of the tx case? If so I built one from the book but can't honestly say that I had much luck with it, probably due to my home etched boards and cooking transistors. Both RM and RCM&E published systems iirc the RCM&E one started on 27MHz and a 35MHz update was published using revised coils and filters. Was it also sold as a kit under the name Viking?

[Robin Colbourne]

This RCM&E cover shows the homebuilt set Nick Cripps mentioned and that I recall.

RCM&E May 1979

List of R/C Equipment article PDFs

[Toni Reynaud]

I built the Dave Platt outfit in 1980 or thereabouts while in Germany with the RAF. I added an earphone socket to the Rx so that I could check that there was no CB activity on my channel before flying. Used it for years.

[Phil Green]

Posted by John Wagg on 10/12/2020 14:23:02:

Today's radios are generally 2.4 GHz and I don't know of any published DIY designs and probably not worth it.

Some of us try to support the 'E' in RCM&E and some like John question its value.  With the proliferation of RTFs you could equally say that scratch building is 'not worth it'!  
There are many facets to this hobby and you're denouncing one on the basis that you're unaware that many of us homebrew on 2.4ghz. There are several published DIY 2.4ghz designs, and all current multimode modules are based on hobby projects. Whether its 'worth it' is down to the individual - on mode-zero right now for example is a project hatching which will combine all the transmitter electronics including encoder and RF into one module. Gary has stated that his interest is more in electronics than flying, so might find DIY worthwhile 

Cheers  
Phil

 

 

 

Edited By Phil Green on 11/12/2020 12:15:30

[John Wagg]

Posted by Phil Green on 11/12/2020 09:35:22:

Posted by John Wagg on 10/12/2020 14:23:02:

Today's radios are generally 2.4 GHz and I don't know of any published DIY designs and probably not worth it.

Some of us try to support the 'E' in RCM&E and some like John question its value. With the proliferation of RTFs you could equally say that scratch building is 'not worth it'. There are many facets to this hobby John and you're denouncing one on the basis that you're unaware. Many of us homebrew on 2.4ghz. There are several published DIY 2.4hz designs, and the whole multimode thing is based on amateur projects and whether its 'worth it' is down to the individual. On mode-zero right now for example is a project hatching which will combine all the transmitter electronics including encoder and RF into one module. Gary has stated that his interest is more in electronics than flying, so might not share your opinion

Cheers
Phil Edited By Phil Green on 11/12/2020 10:10:21

Yes Phil you are quite right. I have always built my stuff just to use and not just for joy of the electronics. Although I do like to understand how a thing works.

Having said that I have recently modified a Futaba Conquest to 2.4 just for the fun off it and there is not a better feeling when things work.

My own background for RC kit building started with a heterodyne single channel followed by the Microtrol then the RCM&E. The Microtrol was built at a time when, as a young family, spare cash was at a premium and luckily I had access to parts and equipment through my work.

I still have some of the kit receivers I built with the RCM&E bottom right. All 35FM and still working.

Cheers

[Paul Newell 2]

Hi,

I don’t normally contribute to forums but this topic kicked off a nostalgia element in me.

As mentioned in previous posts, I was the designer of the ‘Microtrol’ system, published in book form by Radio Modeller. ‘Theory and Practice of Model Radio Control’ first came out in 1972. Two further editions followed, the content being updated to reflect the technical advances of the decade.

All the equipment was on 27MHz and used AM (amplitude modulation) for the radio transmission. Around 1979 we gained 35MHz for aircraft use and closer spaced channels. This was partly due to the adoption of FM (frequency modulation) for the transmission.

A new ‘Microtrol’ system was developed and a complete revision and re-titled book was published in 1982 ‘Radio Control – a handbook of theory and practice’. Several things happened around this time.

• Japanese designed equipment started to become available at prices that became competitive with home construction kits.
• The hobby trade adopted a technical approval procedure to protect the integrity of our frequency usage – an early version of the concept now represented by CE marking.
• Radio Modeller magazine (but not the books) was sold to the publishers of RCM&E.

All in all the wrong timing for bringing out the new book for home constructed equipment!

My own career developed into specialising in the adoption of microprocessors for industrial electronics and modelling related activities took a back seat until around 1995.  At this stage I constructed a computerised transmitter, still christened ‘Microtrol’ and utilising the transmission module from the 1982 book as it had passed the hobby trade approval process.

Another upgraded computerised transmitter was designed and constructed around 2006, still using the same 35MHz module.

For a long time my flying interest had been electric launched thermal soaring gliders and in 2009 I started to fly competitively in national and international competitions. This very much coincided with 2.4GHz coming in and I bought my first ever commercial RC outfit, a JR.   More recently this has been replaced with a latest state of the art top end commercial product.

What can I say, modern servos have so much more precision than what we had in the earlier times. The transmitter/receiver system has a matching precision in the handling of the control commands and the integrity of the radio communication link is something we could never have imagined in the days when I first began designing equipment.

I am still a very active flyer and take to the air regularly with a type of model where the precision of the control equipment can really be appreciated. Every time I take to the air, it brings home to me just how much we have progressed over the past 50 years. It was exciting to have contributed a small part of it.

Edited By Paul Newell 2 on 11/12/2020 18:17:07

Edited By Paul Newell 2 on 11/12/2020 18:19:11

[Peter Christy]

Paul: Its great to hear from you! FWIW, I still have my first edition for your book, and it was that that inspired me to start designing and building my own systems a few years later!

In my mid-teens, I had devoured the American RC Modeler magazine, especially the "Digitrio", and later "Classic" construction articles, but it was your book that joined all the dots for me, and led to my eventual career in electronics. I owe you a huge debt of gratitude!

Glad to hear that you are still active! I'm sure if you follow the links I posted earlier in this thread, you'll find an abundance of like-minded folks still developing home built and designed equipment - even 3D printed stick assemblies - for enjoyment!

And I can assure everyone, that if you think your first successful solo flight was an experience you will never forget, doing it with a RC system that you have designed and built yourself is even better!

--

Pete

[Paul Newell 2]

Hi Pete,

Have to say that, like you, I was inspired into electronics by others from the modelling fraternity. In my case it was Idris Frances of Flight Link. At a later stage my RC involvement introduced me into a business partnership with Peter Cabrol of C&L who earlier had produced the Climax R/C equipment.

Apart from mundane industrial applications I designed equipment for fully automated leisure industry ride systems, laser lighting controls for ‘the Who’ and we even used variations of the R/C systems for ‘Spitting Image’ and Ford tractors.

Copies of my books and other Radio Modeller publications are on my bookshelf. Examples of most of the Microtrol equipment are still in the loft, except for that first Tx with the awful large air spaced coils in the output circuit. - I robbed the Tx for the stick assemblies.

Top specification equipment these days is beyond the facilities available to home constructors as it invariably uses tiny complex components that can only be assembled into circuits using automated production machines. 2.4GHz is derived from Bluetooth and Wi-Fi and at these high frequencies there is little latitude for inaccuracies in the physical aspects of assemblies.

[Gary Morton]

Posted by Bob Cotsford on 10/12/2020 23:21:54:

Was the Microtrol the homebrew that used a massive PCB filling most of the back of the tx case? If so I built one from the book but can't honestly say that I had much luck with it, probably due to my home etched boards and cooking transistors. Both RM and RCM&E published systems iirc the RCM&E one started on 27MHz and a 35MHz update was published using revised coils and filters. Was it also sold as a kit under the name Viking?

Indeed that was the design which I attempted to build and failed miserably! I really wish that I still had the home made PCB.

The author has posted in this thread. I have two of his books, but I have never tried to build anything else ... but hopefully that will change soon. Mine is the second edition from 1974 (older than I thought).