hi to all members

can any one change the Mhz of our radio like my is 40mhz can i make 72 mhz?

what to do

If it is a module based radio, then yes it should be fairly easy. Otherwise it would be hard. Even if you figure out the circuitry, it would require serious testing equipment to fine tune it and get it proper.

You can always do the Assan 2.4Ghz hack instead, right ? That would give you a nice solution.

Agree to anwar. changing the circuitry is a difficult task....
My Q: For Eg. my tx is having a xtl of 72.810 Mhz with matching reciver xtl. CAN i use some other xtl set, of different channel like 72.510...............

There is "lo" band, "high" band and sort of "no band" receivers, at least in Futaba world.  The difference is how the "centre frequency" is tuned.  So low band receivers can take any channel/crystal in between 11 and 35, and high band ones can take any channel between 36 and 60.

So typically it is very safe to jump INSIDE these bands. 

JR etc have no such restriction, so you can feel free to jump to any channel.

While the receivers are designed to accept a range of crystals, Futaba transmitters have a more narrow tuning. I have observed signal level decreasing if you shift more than 2-3 channels.

The output cicuit in a Tx and the front end (input ) of Rx is tuned (optimised) for one frequency band(the crystals  which comes with the set) but the Tx Rx will work efficiently up to 2-3 bands up and down.
Changing the frequency crystal results in less output of Tx and less sensitivity of Rx.
Further this effect is less pronounced at lower frequecy (eg27,35,36,40,41mhz )and more pronounced at high frequency(eg 72,and 75Mhz.)This is why there are Hi and Lo in the 72 and75Mhz band and no such thing in the lower band frequecies(27-41Mhz)
Tuning of Rx  front end and Tx output stage is easy and requires minimunm of equipment,but but you should be familiar with the circuit and know which coils to tune.Not advisable. Change frequency only if absolutly essential.(especialy in 72 and 75Mhz)

Jitender

On the TX side, the manufacturers always specify that the TX has to be sent back to them for re-tuning. I have seen multiple people change it themselves locally though, without issues (at least so far).  Can't remember how vast the change was. 

I guess they must have been close enough to the original channel, as they just wanted to have a frequency/channel of their own in the field that does not conflict with anyone who flies regularly at the same time as them (during those days when 72Mhz and frequency boards were the norm).

Nice Replies..........thanks everybody.......in short..........not to take panga with your costly toy.........

Yes. 

Unless if you are really worried about someone shooting you down with a conflict, then move no more than 2 channels up or down on the TX side. 

And be aware that receiver tuning (based on crystals) is done for some intermediate frequency, so there is more flexibility there. This information comes in handy when you are trying to sell or buy receivers.

It is not that the effect is less pronounced. The real reason is that the "spread" between the highest and lowest allocated frequencies, is much wider in the 72 & 75 MHz bands ( 980 & 580 kHz. respectively). In contrast the spread is only 350 kHz in the 35 MHz band. This reduced spread is because of less channels and closer (10kHz) spacing.

Is there any equipment or any device/tx ever built (not commercially) from which you can take out any frequency/channel any time? i have tried googling a lot but unable to fine suitable key words..............
Sandeep

Assuming I understood the issue, all the higher end radios do that (like the Futaba 12 and 14 channel ones).  For example, on the Futaba 12FG, one can put a Futaba MZ-FM module (instead of the 2.4Ghz module), then one can choose any channel (11 through 60) just from software.  One can have different models on different channels, and when you jump from one model to another, the transmitter will begin to transmit in the right frequency (without having to physically do anything).

On many mid range TXs, you can get synth transmission modules where you can turn two pots to pick any channel.  Many Futaba 9C users have it (http://www.rcuniverse.com/magazine/article_display.cfm?article_id=542).

Google for "synthesized module".

Nice information.....thanks Anwar............

Is it any way to put 40 mhz crystal in 36 mhz radio (futaba t6xa).
What are the tuning procedures?
Need some information over this.

there are stages / sections in these RC devices, 1 control unit, 2 Radio, radio transmit signals, it can be digital, or Analogue, there are radios designed to harness these 2 types, RC set needs a reliable radios, that is why advance sections in radio design concept have taken over outdated, well the frequencies you mentioned has 40 Mhz and 72 Mhz  one cannot change directly it needs the processor or the control IC component to understand or take the signal through and pass it the Radio and handshake the receiver, the primary stage if modified little near 40 Mhz so that the control IC detects feed-in signal, all such IC are designed according to it regular usage, when it is frequency based, whether crystal (Resonant) or radio..