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Author Topic: changing 35mhz to 40mhz rx-tx  (Read 7393 times)

sub john

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changing 35mhz to 40mhz rx-tx
« on: October 19, 2011, 09:27:27 PM »

I have read on  a few forums about people saying that 40MHz radios are probably going to be stopped being made because of 2.4ghz but i my self can not see why this is a problem there is some good 35MHz radio sets being sold on ebay and other places very cheep and are just about given away as no body wont's them for model planes any more and these are ideal to be changed to 40MHz if needs be. I have just changed a zip 9 futaba TX to 40 MHz   was all done in 15 Min's just waiting for crystal to change receiver to work on 40MHz, the receiver is PCM. The RX unit is the hardest bit to change has you have to change caps to return RX unit to get it right but doing this its not rocket science it takes more time to set up the test gear than it does to do the modes, i know that people will say that it won't be legal to do this and use it but i can't see if it is set up right there being a problem no body will no the difference between a brand new 40MHz set and one that has been modded
          JOHN
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Umi_Ryuzuki

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Re: changing 35mhz to 40mhz rx-tx
« Reply #1 on: October 19, 2011, 09:33:50 PM »

Typically the reciever, and the transmitter have to be retuned using an occiliscope to change the FREQUENCY from
35mhz to 40 mhz. Changing crystals will only change the CHANNEL, not the FREQUENCY. If you put 40mhz crystals into
 35mhz radio equipment, the equipment will not function properly.  I know that lower frequencies are favored for
RC submarines, but Air and Ground frequencies should still remain separated. I know I was at the pond a couple of
times when RC helicopter pilots would come over to the pond to see if anyone was on an air frequency. This would
alway happen when a friend was trying to sneak a sail with the one model that he had the airplane equipment in.
And He would always say, "no one would be in the park with an airplane."
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Subculture

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Re: changing 35mhz to 40mhz rx-tx
« Reply #2 on: October 20, 2011, 03:10:18 PM »

I think for most modellers, retuning R/C sets would be akin to rocket science.

There must be thousands of 35mhz sets out there gathering dust. AFAIK, it's not against the law to retune these sets, but the elephant in the room is how things would pan out with organisers if you wanted to use such tweaked sets at shows, especially if there are flying displays there too.

For instance, being reluctant to part with my perfectly serviceable TX's, but acknowledging the benefits of the newer systems, I have converted a couple of my older R/C sets to dual 2.4ghz and 35/40mhz using the DIY conversion modules you can purchase very inexpensively online. However, I understand these DIY modules are frowned upon by some organisations, and I don't think you can use them at shows or public displays.

This is understandable, as the quality of installation can be very variable, and it doesn't really come under any form of professional quality control.

Although the big Japanese and European manufacturers are gradually fazing out their low frequency R/C systems, it appears to be a (smaller) market that Chinese R/C manufacturers are happy to cater to- e.g. WFLY, Corona etc.

Build quality and  specification of these Chinese sets aren't always as good as the Japanese sets, but they seem to be getting better all the time, and at least some form of R/C equipment will be available for the foreseeable future for those entering the sub aquatic side of the hobby without having to break out the soldering iron.

sub john

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Re: changing 35mhz to 40mhz rx-tx
« Reply #3 on: October 20, 2011, 09:27:23 PM »

Reply#1
HI UMI RYUZUKI
You said changing crystals will only change the channel not the frequency but changing the crystal does change the frequency thats what gives you the channel spacing weather its 35 MHZ or 40 MHZ units can be tuned using a spectrum analyzer
    All the best John
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JB

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Re: changing 35mhz to 40mhz rx-tx
« Reply #4 on: October 20, 2011, 09:55:19 PM »

As a model aircraft flyer for 20 years I think I should offer some advice on this subject.

35MHz is legally allocated to flying models only in the UK, the reason is clear, anyone operating a surface model on 35MHz be it boat car or whatever is breaking the law and could interfere with an model aircraft's control within range of the transmitter, possibly up to 1 mile distant.

35MHz and 40MHz are different in the circuitry..as is 27MHz and 2.4GHz...changing a crystal will not change the circuit design and will not work, a change of 'module' would be needed to achieve this, you can change 35MHz to 40MHz or any other 'band' by changing the module which is the only way it would work.

JB.
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JB

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Re: changing 35mhz to 40mhz rx-tx
« Reply #5 on: October 20, 2011, 10:01:08 PM »



Also 35MHz is still used extensively in my flying club, a number of members don't want to scrap their large collection of usable gear.. as was 27MHz until only a few years ago, a model shop I use has 27meg still for sale..new..nothing wrong with it except the CB radio craze killed it off for aircraft.

I've just bought a new 2.4GHz set for my next boat project ok2
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Subculture

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Re: changing 35mhz to 40mhz rx-tx
« Reply #6 on: October 20, 2011, 10:05:15 PM »

I understand the logic behind reserving 35mhz for aircraft use, but as a flyer also, I always had in the back of my mind, that whilst flying my model, someone could quite legitimately switch on a transmitter on the same frequency in a nearby workshop testing out an aeroplane etc., and I'd be blissfully unaware of this until experiencing interference of some kind.

Just one of the reasons why I much prefer 2.4ghz. If only it worked beneath the brine!

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Re: changing 35mhz to 40mhz rx-tx
« Reply #7 on: October 20, 2011, 10:13:13 PM »

I've seen that happen on the flying field! the peg board broke down sometimes %) anyone new usually has 2.4 now, its only the old MOG's who stick to 35 and wont move on!

I've gone 2.4 so I don't care anymore :D

JB.
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sub john

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Re: changing 35mhz to 40mhz rx-tx
« Reply #8 on: October 20, 2011, 10:31:09 PM »

HI Subculture
Yes it has always bothered me on flying on 35MHZ i remember some body switching on a 35MHZ TX unit in the car park and some one was flying on the same channel needless to say the plane ended up in a black bag i myself fly every thing on 2.4 if you have got 6 grands worth of F3A pattership in the air the least thing you need is some plonker switching on 35MHZ and shooting you down and i will need a black bag to take it back home . I would say that i would never fly a plane on 35MHZ again as it is to dangerous to many things to go wrong. l
   

Some one said that the circuit for a 35MHZ set and 40MHZ are completely different but sorry to say there is not much difference at all unless one is 35MHZ AM and the other is 35MHZ  FM

Subculture won't to get back on to low frequency radio links for subs somebody has just given me a 7ft uboat hull and deck when i get to build it i don't no seem to spend most of my time designing electronics at the moment
    John
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JB

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Re: changing 35mhz to 40mhz rx-tx
« Reply #9 on: October 20, 2011, 11:40:25 PM »

HI Subculture
Yes it has always bothered me on flying on 35MHZ i remember some body switching on a 35MHZ TX unit in the car park and some one was flying on the same channel needless to say the plane ended up in a black bag i myself fly every thing on 2.4 if you have got 6 grands worth of F3A pattership in the air the least thing you need is some plonker switching on 35MHZ and shooting you down and i will need a black bag to take it back home . I would say that i would never fly a plane on 35MHZ again as it is to dangerous to many things to go wrong. l
   

Some one said that the circuit for a 35MHZ set and 40MHZ are completely different but sorry to say there is not much difference at all unless one is 35MHZ AM and the other is 35MHZ  FM

Subculture won't to get back on to low frequency radio links for subs somebody has just given me a 7ft uboat hull and deck when i get to build it i don't no seem to spend most of my time designing electronics at the moment
    John


 {-) {-) {-) {-) {-) {-)

Well...that 'someone' was me..JB...and I'll not bother wasting my time replying to any of your writings...and another point...don't try to change what I have written...OK? 'different' is not 'completely different' ...what you are trying to suggest just won't work.

Don't blow yourself up now will you..... %)

JB.

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Circlip

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Re: changing 35mhz to 40mhz rx-tx
« Reply #10 on: October 21, 2011, 12:16:19 AM »

Quote
HI UMI RYUZUKI
You said changing crystals will only change the channel not the frequency but changing the crystal does change the frequency thats what gives you the channel spacing weather its 35 MHZ or 40 MHZ units can be tuned using a spectrum analyzer

 Yes, the crystal does change the frequency, but within close limits of the base frequency be it 35 or 40 moggies. The basic oscillator circuitry is different by changing a few capacitors and also the number of turns on the oscillator coil. It may be possible to overdrive a 35 meg circuit to 40 by "Tweaking" the coils looking at a trace on a spectrum analhizer it won't do it efficiently cos the base circuit ain't designed to work on 40 moggies.

  I've been shouted down on this forum before on the basic operating regime we Aero guys were always taught was to turn the receiver on before the transmitter to ensure that no one else was using the same frequency to bring yer pride and joy down to firma terribly. Can't do that with toy boats cos of the electronic gizmo's, but it takes a special kind of idiot to disregard anyone else's safe operation when flying, but yes, there are loonies who refuse to change from the illegal air frequencies when operating surface models.

  To quote the sixties film, "I'm alright Jack"

   Regards  Ian.
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Re: changing 35mhz to 40mhz rx-tx
« Reply #11 on: October 21, 2011, 05:29:56 PM »

Some of the responses seem to be a bit acerbic in this thread. I didn't recall seeing anything in the original post about just changing crystals or tweaking. Looking at the other stuff John has done with his Gato, it looks to me like he knows what he is doing.

I do know that some people have their radio sets in the States frequently retuned from 72mhz to 75mhz for surface use, quite legitimately by service centres, as the range of equipment available over there is not as good as it is here in the UK.

sub john

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Re: changing 35mhz to 40mhz rx-tx
« Reply #12 on: October 21, 2011, 09:18:12 PM »

HI SUBCULTURE
  Thanks for comment on seem to no what I'm doing it does seem to be that some people do seem to throw there DUMMYS out of there prams easy. One of the things with changing radio's specially on RX yes you have to get xtal oscillator to run at right level but what is more important is to get the RF input set up on RF front end of RX other wise will not have full range. One thing i would like to say it does work its sat on the bench finished works just fine,

You said that some of the guys in the USA i think you said use 72 MHZ and change them to 75 MHZ didn't no that they could use 75MHZ, do any of the guys out there have problems with range under water as it seems a bit high in frequency for under water
   John
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Re: changing 35mhz to 40mhz rx-tx
« Reply #13 on: October 22, 2011, 06:58:00 AM »

They seem to get the same range as we do with 40mhz.

Circlip

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Re: changing 35mhz to 40mhz rx-tx
« Reply #14 on: October 22, 2011, 11:09:42 AM »

Ah for the good old days of 27moggies AM super-regen sets, there seemed to be far less "Accidents".

  Unfortunately, the original title of the posting makes an assumption to the uneducated that it's just a quick twiddle and a crystal change. Further posting reveal buzz words like "Test Gear" and "Spectrum Analyser" but who fully reads postings anyway?

 In a much earlier age, when 27mogs Superhets were prevalent, if you had to explain why it was imprudent to fly a "Brown" flag while being on a "Blue" crystal to some, what chance do you have when the also comparatively "Easy" conversion of swopping a 35 for a 40 beckons the uneducated?

  Yes and then there's Hitec's cheap solution to the great drift to 35 mogs when the C/B brigade swamped the 27 band. 35 megs AM what a brilliant idea, certainly made for a bit of head scratching but did ensure that Hitec did have a monopoly on 35 meg AM crystal supply when FM was the preferred (although more expensive) systems.

 
Quote
As a model aircraft flier for 20 years I think I should offer some advice on this subject.

  Yes mate and as a toy aircraft flier of more than 50 years, some of us have erased the Video and long since used the Tee-shirt as dusters. 27 AM still works well as most of the C/B ers have long since burned out there burners and let dust settle on there 27FM legal sets. I wouldn't advocate its use on yer super dooper zoomaplane, but if the spectrum of available channels on 35 mogs FM is too narrow, life is really sad.

  Hopefully you're going to remove the "Type Approval" stickers from the 35 mog transmitter Sub John ? I would have though you would have got far bigger frowns by this conversion rather than turning off the whole "front end" of a 35 set and substituting a 2.4 gigly one?

  I think the frown bride are far more bothered about the "Quality" or lack of by some of the far eastern manufacturers, especially when applied to some of todays electric high speed buzz saws?

  No dummy spitting, just a clarification for those who might not understand the intricacies of smoke filled containers.

  Reghards  Ian.
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malcolmfrary

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Re: changing 35mhz to 40mhz rx-tx
« Reply #15 on: October 22, 2011, 01:57:47 PM »

For a truly legal conversion involving the changing of components on a type approved board, you do need as a minimum, certificated, type approved, calibrated, test gear.  That means a full grown service center, who will be entitled and qualified, having tested it, to apply the appropriate sticker to indicate that it is a legal set.
The components on the board set the basic frequency band that the set will operate in - the crystal fine tunes and stabilises the set down to the actual channel to be used.
Top line manufacturers often have conversion modules for transmitters.  The receiver is a module all of its own, and while conversion is theoretically possible, it is a job for someone with a workshop full of the appropriate gear.  It one of those "If you have to ask, best not try it" sort of scenarios.
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essex2visuvesi

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Re: changing 35mhz to 40mhz rx-tx
« Reply #16 on: October 22, 2011, 03:31:53 PM »

a few years back when I used to fly planes the flying club issued you a channel.... that was YOUR channel and no one else was allowed to use that channel
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Re: changing 35mhz to 40mhz rx-tx
« Reply #17 on: October 22, 2011, 05:06:00 PM »

a few years back when I used to fly planes the flying club issued you a channel.... that was YOUR channel and no one else was allowed to use that channel
OK as long as there are less members than channels.  Tends to fall over a bit if a guest turns up.
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essex2visuvesi

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Re: changing 35mhz to 40mhz rx-tx
« Reply #18 on: October 22, 2011, 05:16:20 PM »

True but it worked most of the time
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