900 MHz or 2.4 GHz what is better - Page 2 - RC Groups
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Jan 12, 2008, 06:24 AM
Proud to eat Kraut ;-)
Julez's Avatar
I think that spread spectrum on 900MHz would be the best RC frequency.
It combines the penetration of normal MHz systems and the reliability of most new 2.4GHz systems.
In RC applications, we already have more bandwith than we need with 2.4GHz. Thus, it would make more sense to make the signal reception more reliable, and this can be done by moving to 900MHz.
This frequency is IMHO the best compromise between
- lower frequencies (good penetration, bad security against interference) and
- high frequencies ( not so good penetration, high security against interference)

If the features (FHSS) mentioned by XPS ( ) exist in reality, then a 900MHz FHSS system will be hard to beat in terms of reliability, if well implemented.

Cheers,

Julez
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Jan 12, 2008, 07:51 AM
Registered User
I don't know if that's a good idea in europe. We are only allowed to be in 1Mhz range. I will wait and see.
Jan 12, 2008, 08:47 AM
Proud to eat Kraut ;-)
Julez's Avatar
I just read its 7MHz, and as usual, power regulations are much more complicated here I read only 25mW are allowed, but I dont know for sure.
As you said, time will tell.
Jan 12, 2008, 02:38 PM
Registered User
If 900Mhz has so many advantages why did they not develop it first


Heather
Jan 12, 2008, 02:48 PM
Registered User
I think they started with off the shelf components so they could get a product to the market as quickly as possible. They then realised the limitations of 2.4 and started exploring other possibilities.

I suspect they developed their own RF solution rather than buy RF modules, that's why they need FCC certification.

900/868 MHz is not necessarily better than 2.4 GHz. It really depends on which part of the spectrum is quieter in the area people fly.
Jan 12, 2008, 05:17 PM
Registered User
Why is it 868 mhz in the rest of the world? Is there something else on 900 there and not in the USA.
Jan 12, 2008, 05:32 PM
Kou
Kou
Registered User
No, just regulations... I believe. That is the advantage of 2.4GHz. No freq to worry about between countries.

MK
Jan 12, 2008, 06:26 PM
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pda4you's Avatar
Quote:
Originally Posted by Bob Finlay
Why is it 868 mhz in the rest of the world? Is there something else on 900 there and not in the USA.
Because I think other regions of the world use 900MHz for cellular - not positive.

Mike
Jan 12, 2008, 06:46 PM
Registered User
Yes we in europe have 900 mhz for GSM phones "cellular"
Jan 16, 2008, 01:20 AM
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skubacb's Avatar
Not sure if I remember this correctly (from the AMA show), 900mhz may not be available for Europe because of frequency regulations.

Big reason for 900mhz is that it is not at the resonance frequency of water. I.E. microwaves ovens at 2.4ghz. Also, the ability to travel though carbon fiber. Range will be somewhat similar to the 2.4ghz system which should be more than enough for any RC use.

Downside will be cost. I understand that the cost will be somewhere around what Futaba charges for their 2.4ghz system. This I understand was part of the hold up on the 900mhz system. The chips until recently were quite expensive.
Jan 16, 2008, 01:30 AM
The reviewer
XJet's Avatar
Quote:
Originally Posted by skubacb
Big reason for 900mhz is that it is not at the resonance frequency of water.
What utter piffle!

That has nothing to do with anything.

The reason for 900MHz is simply because its another ISM band which allows license-free low-power transmissions.

Where do you get this stuff from?

Quote:
Also, the ability to travel though carbon fiber.
More rubbish.

For someone who is so quick to criticize the knowledge and qualifications of others you're embarrassing yourself with this posting.

900MHz won't travel through carbon significantly more easily than 2.4GHz will. The advantage of 900MHz in a carbon plane is that the antenna is long enough that you can route it outside the fuselage.

Quote:
Range will be somewhat similar to the 2.4ghz system which should be more than enough for any RC use.
Sigh! The path-loss for 900MHz is lower (8.5dB from memory) than 2.4GHz but the range is determined by a number of factors. Watt for Watt a 900MHz system will have a significantly greater range than 2.4GHz.

If you're going to criticize others for talking BS on subjects they know nothing about it would be polite to refrain from doing the same.
Jan 16, 2008, 01:36 AM
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skubacb's Avatar
XJet, wrong again. Water absorbs 2.4 much more than 900. Thats why a microwave is 2.4. That is one reason why 900 is preferred in some cases over 2.4
Wrong again. Try some tests with a carbon fiber fuse at 2.4 and 900. Weave is important too.
Range: Wrong again. Depends on the antenna design and power levels. The new system will be about the same range as the 2.4 system. But of course you have no information about the new system.
Jan 16, 2008, 09:53 AM
Proud to eat Kraut ;-)
Julez's Avatar
Quote:
900MHz won't travel through carbon significantly more easily than 2.4GHz will. The advantage of 900MHz in a carbon plane is that the antenna is long enough that you can route it outside the fuselage.
I agree on this.
We all know that neither 72MHz nor 2.4GHz work well inside CF. Why should any frequency in between work better?
Jan 16, 2008, 10:36 AM
Registered User
Quote:
Originally Posted by skubacb
...
Range: Wrong again. Depends on the antenna design and power levels. The new system will be about the same range as the 2.4 system. ...
Not according to Digi/Maxstream: http://www.digi.com/technology/rfmod...0solutions.jsp
Jan 16, 2008, 07:41 PM
Dick Corby
altacom's Avatar
Quote:
Originally Posted by Heather
If 900Mhz has so many advantages why did they not develop it first


Heather
In the video from the AMA convention, i believe that Ji stated that they were developing the 2.4 and 900 systems at the same time. Just that it apparently took longer to get the weight etc. down. And now waiting for FCC approval to release it. He stated that they even have the plastic cases on time for this release.


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