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Author Topic: RC  (Read 3107 times)

Willit

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RC
« on: March 01, 2008, 07:11:20 pm »

Hi all
I'm going to sound like a complete jackass here but here goes.  Basically I am somewhat confused about RC frequencies in the 27 and 40 bands.

I have a chart showing all the different frequencies, and I rather gathered from it that you could operate a model on the 27.145 band alongside one of 27.195.  Dad says you can but you obviously can't because we tried today and it didn't work.

So how much of a gap do you need between the 27s before they won't interfere with each other, or do all 27s interfere with each other anyway no matter what 27pointwhatever they are?

I've operated my tug on 40 meg alongside people with boats on 40, and they didn't interfere with each other at all.  I don't think the gap between the frequencies was especially big either.

So is it just 27 being finicky, or does this apply to 40 too?  Is it simply the fact that .145 and .195 are so close to each other?

you can tell I just enjoy building playing with boats and not caring too much for the electronics side of things (dads side of things!).  I can do wiring and set up RC no problem but I think its time I understood fully about this!

thanks

Matt
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malcolmfrary

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Re: RC
« Reply #1 on: March 01, 2008, 08:50:30 pm »

Being a long time user of 27, I have never had the problem.  I tend never to bother about the actual frequency, just the colour coding of the crystal.
It is possible that one of the sets is duff.  This could be either a broken set, or an RTR with no crystal changing facility, which, from a satisfaction point of view, seem to be designed that way.  These are often designed for low cost, and typically have low power output and poor sensitivity along with poor selectivity.  As a result, they tend to be swamped by anything else anywhere near their band.
Over the years, the number of allocated channels within the band has increased - older equipment can still be used, but there may be some issues when mixing new and old.  An old transmitter might well be producing signal in neighbouring channels, and a receiver might well try to resolve information being broadcast on them.  This may also happen if the sets lack either an FCC (US approval) or CE (Euro approval) label.  This indicates that they where made without troubling the certification authorities, and thus might not conform to any known standard.  Interference is a symptom of this.
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White Ensign

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Re: RC
« Reply #2 on: March 01, 2008, 08:53:33 pm »

Matt, could depend on the frequency. I know that in Germany the helicopters of the ambulance and police use to pop on a band close to the 27 Meg, which brings along massive interferences.
Also could be military the prob as well as High-Voltage masts. So, change the chrystals and if you do not succeed- check out to 40 Meg or much better, 2,4 Gig WLAN.

Hope that was out of any help.

Jörg
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Proteus

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Re: RC
« Reply #3 on: March 01, 2008, 08:55:56 pm »

What radio gear where you using as some will not work with splits, is it ce aproved.
Fredy
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Willit

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Re: RC
« Reply #4 on: March 01, 2008, 09:50:56 pm »

What radio gear where you using as some will not work with splits, is it ce aproved.
Fredy

my Springer tug was using a Hitec Bycmo 27.195 meg set and my friend was using a Dickie on 27.145

this would back up the RTR explanation above.

so if my friends Dickie was upgraded to a set which was still on .145 it would not clash with my boats?
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malcolmfrary

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Re: RC
« Reply #5 on: March 03, 2008, 11:00:24 am »

If both boats are fitted with, and using "normal" radio gear, you should have no more, but by the same token, no less, problems than anybody else.
The fixed single frequency sets do come with a frequency stamped on, but this is generally just to impress, and should be regarded as a loose suggestion rather than gospel, especially if it lacks the CE stamp.  The "proper" sets with interchangeable crystals do transmit and receive on the frequencies stated, and stop at that.
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Bee

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Re: RC
« Reply #6 on: March 03, 2008, 10:52:30 pm »

warning - technical stuff follows.
There is no 'magic' in a radio just because it has crystals. The transmitter is likely to be clean and on frequency. However the crystal in the receiver only means it knows which frequency it should have in the middle of it's band. More importantly the receiver has to have a "narrow IF filter". In older sets this was the little metal cubes with a screwdriver slot in the top. Higher quality sets sometimes advertised more "IF transformers". Nowadays it is doen slightly differently in single chip radios but hence the filter can be less narrow so adjacent (legitimate) frequencies  can get in as interference.
 That's not the end of it. 27 MHz sets are AM whereas 40 MHz are FM. Unfortunately AM is much more affected by this type of interference than FM for the same compromise n the IF design. This is part of the reason Broadcast radio AM is lower quality than FM music channels.
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barriew

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Re: RC
« Reply #7 on: March 04, 2008, 08:41:47 am »

That's not the end of it. 27 MHz sets are AM whereas 40 MHz are FM. Unfortunately AM is much more affected by this type of interference than FM for the same compromise n the IF design. This is part of the reason Broadcast radio AM is lower quality than FM music channels.

I think you will find that 40Mhz 2 channel sets are AM.

Barrie
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DickyD

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Re: RC
« Reply #8 on: March 04, 2008, 09:06:45 am »

All my 40Mhz 2 channel sets are AM. O0
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malcolmfrary

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Re: RC
« Reply #9 on: March 04, 2008, 12:04:08 pm »

While it is true that there is no magic about sets with interchangeable crystals, they have usually been designed to a higher standard than those that dont, which have the primary design aim of low cost.
The only reason that AM is more prone to interference is because interference is , normally, an AM signal, but unwanted.  The RX can thus resolve it and process it on as a valid signal, even if it isnt wanted.  FM, on the other hand, is less prone to that kind of thing.
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Proteus

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Re: RC
« Reply #10 on: March 04, 2008, 12:46:43 pm »

40 mhz Jr sets  where  FM

Fredy
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rcfred

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Re: RC
« Reply #11 on: March 04, 2008, 03:51:28 pm »

Your problem is 99.9 percent certain to be the Dickie receiver which needs the whole of the 27MHz band to operate successfully. Unfortunately, it is not a simple matter of buying and connecting a standard transmitter/receiver. You need to rip out all the electronics and start again - speed control and servo. Probably easier to change bands in your other boat - 40MHz or better still 2.4GHz and never have to worry about crystals again.
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Willit

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Re: RC
« Reply #12 on: March 04, 2008, 04:31:43 pm »

Your problem is 99.9 percent certain to be the Dickie receiver which needs the whole of the 27MHz band to operate successfully. Unfortunately, it is not a simple matter of buying and connecting a standard transmitter/receiver. You need to rip out all the electronics and start again - speed control and servo. Probably easier to change bands in your other boat - 40MHz or better still 2.4GHz and never have to worry about crystals again.

we are gutting the Dickie anyway (this was the plan when he bought it!), we thought the whole thing as bought to be utterly rubbish

I've instructed my friend to bring a large hammer, which will be taken to the Dickie RC gear, as it gave us so much hassle!

As soon as all the gear is here we shall begin wrecking, I mean removing the Dickie RC  O0

thanks guys, thats answered my question perfectly. 
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malcolmfrary

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Re: RC
« Reply #13 on: March 04, 2008, 08:16:03 pm »

If you haven't already found it -
http://www.modelboatmayhem.co.uk/
look at builds, then the bottom right corner has a Dickie conversion.
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Willit

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Re: RC
« Reply #14 on: March 04, 2008, 08:30:46 pm »

If you haven't already found it -
http://www.modelboatmayhem.co.uk/
look at builds, then the bottom right corner has a Dickie conversion.

thanks Malcolm, I've already read all of the conversion builds, and I know exactly what I've got to do.  :)
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