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Author Topic: 35 Mhz to 40 Mhz?  (Read 2991 times)

roycv

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35 Mhz to 40 Mhz?
« on: April 21, 2019, 04:02:34 pm »
Hi all just triggered off by a sale of a 35Mhz Rx as of use to 'fly boys'!  I did a test I have been meaning to do for some time by inserting a 40Mhz crystal into a 7 ch 35 Mhz Rx (Futaba).
 I drove it with my multi but old Fleet Omega set 40 Mhz Tx.  It works fine it passes my length of the back garden and can hardly see the servo test without problem. 

I have had the Fleet set for 15 years and only just noticed that underneath there is a sticker mentioning 35 Mhz. (?)  It was bought as a land use 40 Mhz set, no complaints it has worked great.  I did have initial problems with the non-effective short rubber aerial which works well in the shop but has a range of only 20 feet but substituted that with a telescopic aerial, but that is water under the bridge.
I also recall that someone mentioned there was very little difference electronicswise between the two frequencies at the RF stage in the 35 and 40 Mhtz rx's.

So it would seem do not sell your off your 35 Mhz rx's just put a 40 mhz crystal in.  Anyone got a 35 Mhtz Tx to do the test the other way as well?

Perhaps the range might not be good enough at aircraft distances but with boats one is hardly ever more than 100 metres away.
Regards
Roy
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Klunk

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Re: 35 Mhz to 40 Mhz?
« Reply #1 on: April 21, 2019, 04:29:50 pm »
hi rOY, I HAD HEARD THE SAME MANY YEARS AGO ABOUT MULTIPLEX equipment. As you say good for boats, but would not trust planes or subs!
ps bring it to Black Park in Sept and we can try a long range test
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KitS

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Re: 35 Mhz to 40 Mhz?
« Reply #2 on: April 21, 2019, 06:35:58 pm »
Veeeeeeery interesting.

I have got a 35 Mhz Tx, so maybe I'll give that a go and see what happens.  :-))
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Netleyned

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Re: 35 Mhz to 40 Mhz?
« Reply #3 on: April 21, 2019, 06:44:52 pm »
Why would you want to use a non legal 40MHz system for planes?
35 does not need modding for air use.
Good use for old air gear with 40 MHz xtals if the range is adequate.
The price of 2G4 gear makes it hardly worth using old gear though.
Ned
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roycv

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Re: 35 Mhz to 40 Mhz?
« Reply #4 on: April 21, 2019, 11:08:01 pm »
Hi Netley...  If you read the thread again you will see I was referring to just the range.  Seems to me it is more like recycling gear that might be thrown away. 

If you have not got any old gear then 2.4Ghz is for you but lots of the 35 Mhz RC was very reliable.
Main point was that you can re-use the RC equipment rather than binning it.
regards Roy
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Netleyned

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Re: 35 Mhz to 40 Mhz?
« Reply #5 on: April 22, 2019, 09:07:53 am »
Hi Roy,
I was referring to Klunk saying he would not trust it with planes or subs. It would be illegal for aircraft use anyway. There is a lot of the old 35MHz gear around and I agree it would be a good use for it on small lakes if the range was sufficient.
Ned.
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malcolmfrary

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Re: 35 Mhz to 40 Mhz?
« Reply #6 on: April 22, 2019, 09:14:58 am »
If using it in a public area, it might be a good idea to re-label it to avoid anybody getting the wrong idea that 35MHz is OK for surface.  Thinking of an innocent passer-by, or an obsevant fly-boy.  It might be as well to remember that while some sets work OK on 40 with nothing more than the right crystal, it might not be universally true.
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Colin Bishop

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Re: 35 Mhz to 40 Mhz?
« Reply #7 on: April 22, 2019, 09:23:16 am »
Quote
It might be as well to remember that while some sets work OK on 40 with nothing more than the right crystal, it might not be universally true.

Yes, that is true. I definitely recall reading a while back that whilst some 35Mhz sets will accept 40Mhz crystals, most either won't or will not work properly. It depends on the rest of the TX/RX electronics which are usually different

If it were that easy then there would have been no need to sell separate 35 and 40 gear - just use the appropriate crystals.

Colin
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roycv

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Re: 35 Mhz to 40 Mhz?
« Reply #8 on: April 22, 2019, 10:36:13 am »
Hi Malcolm thanks for you comment, hopefully with the correct frequency flag flying it would be acceptable and go by unnoticed.  I agree some sets may not convert and I do not know detail of the double conversion crystals.
I would think it worth exploring for the 'simple' non computer units to see if they can be re-used in this way.  I had come by an 8ch Futaba Rx which I was going to pass on, now I shall keep it as a spare.
I have so many 40 and 27 Mhz rx's and Tx's that I may as well use them til they fail.  I have lots of crystals although with the 27Mhz FM crystals I have just 3 sets.
I love the classic Futaba M series with the silver case, mine is 27Mhz FM lovely thing to hold and so well balanced.   The near copy by Fleet is not so well balanced, but otherwise looks good.

For non 'black arts' readers multi channel 35 Mhz sets are FM and to possibly convert require a 40 mhz FM crystal,  40 Mhz AM crystals will not work.

I would be interested to hear if anyone else manages to do the conversion, and maybe the ones that do not work.

regards
Roy




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Captain Flack

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Re: 35 Mhz to 40 Mhz?
« Reply #9 on: April 22, 2019, 04:26:58 pm »
Whilst i fully condone your wish to re-use equipment rather than bin it, it might be prudent to think of the insurance implications.  In our current attitude of ambulance chaser solicitors they might see a non standard crystal in a TX as a quick way of dismissing any claim.It may work perfectly but it was not designed to take a crystal other than those designed for it. Not being petty or finicky or pedantic or any thing else, my club would not permit it's use.  We have enough problems with insurances and councils now, without inviting problems.
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Netleyned

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Re: 35 Mhz to 40 Mhz?
« Reply #10 on: April 22, 2019, 04:35:51 pm »
In the legal sense, It would probably be seen as an illegal use. A 35meg tx is still a 35meg tx regardless
of xtal. Claim for pain snakes would find a way to sue methinks.
Ned
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roycv

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Re: 35 Mhz to 40 Mhz?
« Reply #11 on: April 22, 2019, 06:00:17 pm »
Hi Netley I beg to differ!!!  (In the nicest way possible of course)

My Fleet transmitter sold to me from the shop in Fleet as a land based 40 Mhz set has a label underneath which reads

UK. Type approved No SMAE/35/ERA.82/FCS.02.  It has only ever had 40 Mhz crystals in.  Also had the 40mhz Tx flag.

I suspect the 35 and 40 Mhz sets mostly have a similar RF unit, which I believe has to be separately type tested for use.  All the rest of the circuitry is independant of the frequency in use.  The RF oscillator would not differ much in components and the crystal would force the oscillator into the higher or lower frequency depending on what was wanted.

I have another TX from Fleet with the same label underneath.  On the face the labels are Digi-Fleet Omega and the other Digi-Fleet XP/FM.  Again came to me with 40Mhz crystal in place.
The Fleet rx's and all servos esc's etc. all come with non standard connections but these are easily changed.  NB the black and red leads need swapping over.  If you don't it is goodbye rx!

Incidently my first decent RC was from Derek Olley, nice equipment. 

kind regards
Roy


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