rumotech

Are 27 & 75am crystals the same? Can someone shine some light on the subject for me?

redfox435cat

AM and FM are not interchangeable.

In order to change to an entire band requires a full retune of the Transmitter and receiver no you can't change em. If you do do a through range check and make sure anyone around you is not affected. Changing from AM to FM requires an entire board replacement. Some like to come on here and state that only 72mhz is not interchangeable. All bands it’s illegal to change the Tx frequency unless it's designed for it, synthesized, or you are licensed to do so, It may not be illegal to change frequency on 27 mhz but when you do it, that equipment is no longer compliant with it’s part 15 compliance it was licensed under, but then again on 27 mhz no one is going to care.
72 and 75 mhz there is no tampering with the tx in the US again unless you are qualified to do so. You can change Rx crystals within the same band, going for one band to another the circuit would be too far out of tune to be reliable.
Also it's not a good idea to change crystal between brands. Every company does there own specs in regaurdes to the acual crystal cut, so it's a sure bet to take any old cystal and shove it in any peice of equipment and expect it to work. On land based models it not that big a deal it simply doesn't work, but the interferance you may cause someone else can be.

rumotech

I am aware of 2.4 and spectrum. But I picked up a couple of traxxas vehicles for my kids and all 3 on the same channel. Noticed there where 27 & 75 sets of crystals was curious if difference.

redfox435cat

if they are on 27 and 75 mhz they are not the same channel?
your 27 mhz would be like a1 a2 a3 and 75 mhz is channels 61 to 90

on the 27 mhz it wouldn't be a big deal to change the tx and rx crystals to differant 27 mhz channels.

traxxas crystals

like i said stick with the same brand

rumotech

But if I bought a set of 75 crystals would they work in a radio that had 25 crystals.

EloyM

My Feedback: (194)

AM systems are not as critical with crystal selection as are the other types of systems.
     Of the two, 27 MHz is the least  critical, and in almost all cases, properly marked crystals will work in all systems.
     Not so with 75 Mhz - there is a 50-50 chance that they will (won't!) work. On 75 MHz, in the transmitter, some use a full frequency crystal, while others use one at half frequency and double it to the final operating frequency. Somewhat the same applies to the receiver, only the crystal frequency has 455 KHz either added or subtracted to it to arrive at the operating frequency.

     Nothing is damaged by trying different crystals, but while the equipment  might work at close range, it might not have the normal distance. 
   
     Write direct: [email protected], I may be able to help further.  I am an R/C technician. Thanks

tadawson

The bottom line is no - if the radio is on 27MHz, it needs to stay there, although you can change to a different channel within 27MHz to resolve your conflict. The same applies on 75MHz - the frequencies are so drastically different, that the electronics in the TX and RX are very different between the two.

If it is a module based TX, then you could get the 75 MHz module for it, but you would need to buy new receivers for the cars . . .

The good news is that there are enough channel in either band that you can clear your conflict cheaply and easily by changing crystals to a different *channel*within 27MHz . . .

- Tim