Tuesday, February 27, 2007

New 2.4 GHz Spread Spectrum Developments -- Dave Armitage

Spektrum/JR have introduced the revolutionary new DX7 radio and the first impression is that it is very, very good. From my own testing, and observations it fits very well into the requirements for use in the 2.4 GHz band. The manufacturers have got around the previous DX units range problems as well. A ground range check proves beyond doubt that the DX7 range is more than adequate for any type of model aircraft.

The manufacturer claims that it will give interference free flying of just about any size of model aircraft, without frequency clashes. They also claim a peg board system is no longer needed, but SAMAA still requires using a peg on system on the frequency board to show that the band is in use. The general rule for 2.4GHz streamer colour overseas is black. Anyone using spots on the other legal frequency bands must still have the appropriate streamer attached to his/her aerial.

The radio has been type approved in The USA, Canada, Belgium, Denmark, France, Finland, Germany, Italy, Netherlands, Spain, Sweden, and the United Kingdom. ICASA Type approval for South Africa is also being undertaken and should happen within the next few weeks or so when all the necessary documentation is received from the manufacturers. Type approval is not automatic but with so many countries having already approved the system, there is no reason to believe that it will not be passed. The equipment fits in well with South African specifications.

SAMAA formally approved the DX6 radio about six months ago. The DX7 uses the identical transmitter module to the DX6 so SAMAA approval for the unit is basically in place. This will be finalized once the ICASA Type approval has been received.

The system operates in the 2.4 GHz band using technology utilised by NASA and the US Military. There are 79 channels on the 2.4GHz band and when switched on the transmitter scans for two unused channels. When it finds them, it locks onto them and will transmit on those channels until switched off. Each transmitter has a Global Unique Identification Code (GUID) built in. There are somewhere in the region of 4.3 Billion Guid codes universally so the chances of having two identical codes are extremely remote. The receiver is also "Bound" to the transmitter electronically before use and once "bound" will only respond to transmissions containing that code.

The transmitter aerial is short, about 15 cms long and the receiver aerials even shorter at 30 mm each. There are two separate receivers linked together by a 15cm. cable. Each receiver unit actually has two receiver chips giving a total of four on board and when installed correctly they give very good range coverage though the short Tx and Rx aerials do take some getting used to.

The system has what is called "modelmatch" on board. If the receiver detects that the wrong model memory is selected then it will not respond. Unless you have two identically set up aircraft one cannot use the " I had my transmitter on the wrong model" excuse ever again.

Other claimed advantages of the system are that the long lead interference problems do not occur. Quick test reports from overseas also state that it will work with the receivers totally enclosed on a carbon fibre fuselage. These will need further exploration though.

A check through many sites on the web show that the equipment reports are only good and in some case the claims for capabilities are quite extraordinary. The set is supplied with four digital servos and a 1100 Ma/H receiver pack. The transmitter also has a 1500 Ma/H NIMH pack installed.

ICASA state that although the 2.4 GHz band is licence free, they do want the equipment to be type approved, and incidents of interference will not be investigated by them.

This equipment is a major leap forward in Radio Control Technology and should make the flying of model aircraft very much safer.

It needs to be said that although many claims are made for this equipment it may not be the "Be All and End All" for Aeromodellers. SAMAA will keep a watchful eye on the use of the systems and will review the situation in about six months' time.

Finally it has been announced that 2.4Ghz Spread Spektrum modules for the larger radios of most makes will soon be available. Don't despair your JR 9X2 and JR10X will be compatible as will the Futaba 9CAP and even the 14 MZ

1 comment:

CrazyErick said...

I have been using the DX7 for about 3 months now and found it to be a great radio. I can report no interference thus far. Also the idea of not having to worry about being on the same frequency as someone else is peace of mind.

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