I wanted to know whats the
difference between a simple reciever n a synthesized rx.
There's also single conversion n dual conversion.
What do they mean.

FM receivers (as opposed to 2.4Ghz receivers), work on a set number of "channels" within the "band" they are built for.  For example, a 72Mhz band FM receiver will work on channel 11 (72.010Mhz), channel 12 (72.030Mhz), channel 13 (72.050Mhz) upto channel 60 (72.990Mhz).

So within 72Mhz, there are so many channels, and the channel a particular receiver listens on is determined by the "crystal" inserted into the receiver.  This is what allows various people to fly FM at the same time, as they pick different channels for each (both on the transmitter and the receiver). This also means that you have to hunt down the right crystal for your particular channel, so that it matches with the channel *your* transmitter is transmitting on.

Synthesized receivers remove this limitation of having to source separate crystals by either having dials which can be turned to select the channel you want to use (like Futaba R319DP)), or my listening to the most powerful transmission around and then "remembering" it during the "bind" processs (like the Corona ones).

Dual conversion receivers shift the signals down twice, and the claim is that this allows for better selectivity/filtering.  But this is highly contested, and the fact that JR does not have any dual conversion is an indication that the advantages (if any) are fairly limited.

The important thing is that if you have a dual conversion receiver, you have to get a dual conversion crystal. 

And there is no concept of dual and single conversion when it comes to transmitter crystals. 

Overall, the hassle of sourcing the right crystals is one another reason why 2.4Ghz is becoming ever more popular these days.  Just see the "Wanted" board on this forum, to see how people are having issues with getting the right crystals.

Here is a long but thorough investigation of the single versus dual conversion issue.

http://www.bergent.net/SC-DC.pdf

If don't want to read the whole thing, just read the last page

That means getting a fm radio set now means getting mad looking 4 crystals later.
The 2.4 ghz seems gud with rcforall offer.
Anyways don't these 2.4 ghz radio use crystals.
Is a reciever 4m a brand compatible with tx 4m another brand.

Quote from: Anjan on January 12, 2010, 07:29:20 PM
Anyways don't these 2.4 ghz radio use crystals.

No. 2.4Ghz completely avoids the need for *user changable* crystals.  Crystals may still exist as clock drivers inside the receivers / transmitters as electronic components, but they are fixed and not meant to be altered by the end users.

Quote from: Anjan on January 12, 2010, 07:29:20 PM
Is a reciever 4m a brand compatible with tx 4m another brand.

Yes and no.  There are two main classes of receivers, depending on whether they are positive shift or negative shift. When using FM/PPM, Futaba and Hitec (which are both negative shift) will work together.  That is, a Hitec receiver can be used with a Futaba transmitter.  Similarly, JR and Airtronics will work together, as they are both positive shift.

Again, this is where the shift agnostic ones like Corona shines, they will work with all the major brands.

Under FM/PCM, each will only work with its own type, as the PCM encoding is proprietary for each brand.

Thank you Mr anwar for answering my question so
patiently.but im not done yet. I have many more question to ask about so many things.