keong

sorry for this silly question...just wanna know how crystal works with rX??? how come the crystal can know they are 72.8XX mhz and 72.9XX ....anyone has done some research on this???i hope this little piece of clay would have some answer from the experts here..
thanks

JPMacG

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Inside a crystal is a small wafer of quartz. Two metallic plates touch both faces of the wafer and are attached to the two external terminals. The quartz naturally resonates at a certain frequency. Frequency of resonance is controlled by the dimensions of the wafer and the characteristics of the quartz.

The crystal is the frequency determining element in an oscillator circuit. Crystals are an inexpensive way to produce a moderately precise and stable frequency. This is 70 year old technology (at least). There is a ton of information available on the internet and in books. Do a google search on 'crystal oscillator'.

keong

U ARE AN EXPERT BRO!!

rmh

an end of an era approaches -
my new 2.4 radios as well as all the soon to be available 2.4 radios use no crystals - no tubes no slugs no coils --none of these "mechanical " devices to control frequency
Just like the AM tube car radios of the past - our crystal controlled radios are rapidly being moved to the rocking chair.
But it is good to know the history of how it all got started.
I remember my cousin's cat's whisker radio he made when he was 12.----

Campgems

Dick, don't you find it strange that the engine of all the technology changes, the computers, still use crystals? The crystals are so easy to produce, and thus low cost, that there is a strong economic reason to keep useing them in some applications.

The new 2.4 radios are going to change things no doubt. You know, I don't believe my Futaba 9CAPS with the synthizer module has a crystal either.

Those cat whisker radios, "Crystal Radio" were a lot of fun. Some of the later ones used a 1n34 diode in place of the old Galinium crystal with the wire (Cat's whisker) probe. I even say an article where the soldiers in WWII would use a razor blade in place of the crystal. I never tried that one, but about anything that would work as a diode would be OK.

Don

dirtybird

My Feedback: (5)

The main reason 2.4 gh radios use no crystals is crystals cannot be made to generate that frequency. I bet they would use them if they could. They are simpler and cheaper than any other way to generate a precisely controled frequency.

rmh

not in this case -
the new 60001 rx are just a chip -I bet you could mount the rx on the engine and it would still work .
I have Dx6 and 7 radios
the entire 6001 rx weighs ---3.5 grams- not much more than a crystal in a can and socket and it includes a case and a full hd 6 pin block!
The electronics is a teeeensy weeeensy part of it

Mac_Man_UK

Ok, so what controls the CPU ? That needs a clock for timing purposes !

JPMacG

My Feedback: (2)

I think the reason 2.4 GHz SS systems don't use crystals is because they don't need very accurate frequency control. A spread spectrum transmitter sort of smears its signal over a wide bandwidth and the SS receiver reconstructs the modulation and seperates it from other signals and noise by use of "code" filtering. So it doesn't matter that the frequency of the transmitter may be inaccurate.

Microwave signal sources that require accurate frequency control do use crystals. Laboratory microwave sources typically use 10 MHz precision ovenized crystal oscillators. The 10 MHz signal is multiplied, divided and mixed with itself as necessary to achieve the desired frequency (this is the idea of a synthesized source).

tkilwein

The PLL (Phase locked loop) circuit, (used in a number of syn RX's and TX's) uses a low freq crystal-osc then multiplies it up to the needed freq.
With this you can use a low freq crystal-osc (cheaper) and then the PLL will do its job and output the high freq needed.
With a 25MHz crystal-osc and PLL you can get 2.4GHz freq very easy and with less than 100ps of jitter, 30-80ps typical, just one example.
With one crystal-osc and PLL logic you can get many different freq's verses a crystal for every frequency
I design hardware that goes up past 4+GHz operations using a low freq osc and PLL logic contained in the IC's being used.
Oscillators will be around for awhile in one form or another.

JPMacG

My Feedback: (2)

Here is a not-too-heavy overview of PLLs and synthesizers if anyone wants to read more.

http://en.wikipedia.org/wiki/Frequency_synthesiser

rmh

Yes - -Wilkipedia really does a good job on explanations
BUT they don't show any of the RC stuff described in my 1949 Air Trails

dirtybird

My Feedback: (5)

OK I stand corrected. Crystals and PLL's can be used at 2.4GHZ