my cousin has a question

[sikeymikey]

me and him both have crystals with a 2 on them. and he bought a new radio and mine is 27mhz and his comes with a 75mhz radio and a reciever. so if he runs a 75mhz setup with a 2 crystal can i run a 27mhz system with a 2 crystal.

 

[sprocket6821]

Does it make a difference if i have either a 27mhz radio or 75mhz radio? When i went to Tower Hobbies i picked a cheap radio and it asked which frequency i wanted, and i chose "I have no prefrence, send ANY SURFACE FREQUENCY" i just want to know if this has a different effect? Thanks

 

[Diver6127]

Well,in general I would say that they shouldn' be run at the same time. Reason being is that a friend of mine was using channel 1 on a 75 mhz, FM and another guy was using channel 1 27mhz AM and it caused problems with one of their cars. One would be ok but the other would glitch. The frequencies can "bleed" over into the other and it's just a problem waiting to happen.

To be on the safe side, I would go get another crystal.

 

[SkyMaxx]

Interesting that you would have glitching between two very separated frequencies and modulation types, Diver...but I guess it is possible.

As far as the science behind this kind of thing goes, there should be no problems. 27MHz and 75MHz are fairly well separated. That is basically the carrier frequency for the band you operate the radio in. The numbered crystals are basically channels within that band and add a small shift to the 75MHz to give you a separate frequency within that band.

Further, AM (amplitude modulation) and FM (frequency modulation) are two very different modulation types. If used within the same frequency band and channel you could easily see interference of some sort, but when in separate bands and channels there should be no real interference.

The only thing possible and it is a remote possibility would be harmonics. If the two channels selected within the different frequency bands were close to being harmonics of one another, you might see some small problems. BUT as I said that would be a very remote possibility.

Bottom line: Shouldn't be a problem.

 

[canadian-mgt]

I've never seen channel 2 on a 75mhz radio,I thought 75mhz uses channels 61-90.I've only seen channel 2 on 27mhz.I'm not saying it's not possible,just that I've never seen it.

 

[Diver6127]

It was the first time I saw it. Would've never beleived it if I didn't witness it myself. In theory, it should be ok but would you want to risk it? It doesn't cost much to get the crystal set anyway.

 

[SkyMaxx]

You are correct on the channels within 75MHz, but the stickers on crystals may or may not relate directly to the channelization within their respective bands. That kind of depends on the manufacturer. I have seen numbered stickers on crystals from various manufacturers within different frequency bands that had the same numbers on them. I have also seen color coded stickers (mostly within the 27MHz crystals, but not exclusively so.)

It is also entirely possible that they have purchased the wrong crystal set for their radio.

 

[Rolex]

I run FM, and can't run when another guy on the same channel has his AM on. If you remember a thread from last week, my failsafe kicked in and stopped my car, and his went WOT and wrecked my foot before going on it's lid and throwing the con rod.
It's become a rule at the track, go by color or number. It seems to be the crystal, and not the frequency or band.

 

[SkyMaxx]

True, but were you guys both in the 75 or both in the 27 band? As I stated within the same frequency band AM and FM can interfere with each other. It would not be a constant inteference, but it would be noticeable.

 

[Rolex]

That I don't remember. I'll have to check tomorrow. What I do know, is that there wasn't a problem till we got about 20 feet apart, then my car stopped with the failsafe about 50 feet away, and his went nuts from about 30 ft away.

 

[SkyMaxx]

Probably in the same band. AM and FM usually interfere a little when in the same frequency band. In most cases a fully charged AM transmitter over powers the FM at range. You also can see an FM transmitter in one channel within a band interfere with an AM transmitter in another channel within that band due to the modulation that the FM transmitter works through.

I do recall your mention of the incident, but don't remember the entire thread.