kistner

My Feedback: (10)

A couple quick (I hope) questions about transmitters, receivers, and crystals.

Will any fm radio, 27 or 75, work with any fm receiver of the same 27 or 75? ie: should brand 'A' tx work with brand 'B; rx if both are 75mhz using the same crystal?
are there special crystals for fm versus am? I have seen a few on ebay that do not specify am or fm.
I saw some crystals labeled 'am/fm', whats up with that?
and lastly, in the brand 'a' brand 'b' scenario above, can we use brand 'c' crystals?

I appreciate any answers, or links to answers. Trying to learn so I don't buy a bunch of stuff I don't need.

Dr1Driver

Without getting into a lot of technical details:
Some radios will not work with another manufacturer's crystals. It's best to stick with the same brand. Also, some radios will not work with other receivers. Make sure the RX is rated to work with the TX. AM will not work with FM. 27 will not work with 72, etc. Dual conversion/narrow band radios must use the same type of crystal. My advice - Buy a full radio set, complete with TX, RX, batteries, servos, crystals and switch harness. Don't get a slapped together eBay system unless you're SURE everything will work together.

Dr.1

kistner

My Feedback: (10)

Well, that is sort of what I figured. The cheap side of me is drawn to the bits and pieces on ebay that are dirt cheap, but my inexperience with these tells me to stay away.
are there are sites that have a little more technical info for me to read up on?
Thanks for the info.

airbusdrvr

And don't forget there is the positve shift/negative shift incompatibility.

bruce88123

Until you get a lot more experience I suggest avoiding EBAY. Many items are mis-advertised either deliberately or because the seller doesn't know what he is talking about. I've seen used engines sold as new. Radios that don't even work sold as "perfect". It's a trap, be careful. That said there are some bargains IF you know how and where to look and for what.

Rodney

Any fm transmitter will work with any fm receiver on the same frequency if the shift is the same. In most parts of the world, all receivers work on positive shift but; in North America, Futaba and Hitec (there may be others) use negative shift. Some receivers have automatic shift detection and will work with either shift (shift is a function of the transmitter). On AM ( not really AM but simply keying the RF signal on and off at a predetermined rate) all receivers should work with any transmitter on the same frequency.
As to crystals (those in the receiver) there is no difference between AM and FM however, there is a difference in DC (dual conversion) and SC (single conversion) recievers. For DC, the main crystal (there are two in the receiver but only one you can change) is usually 11.7MHz different from the transmitted frequency while for SC (only one crystral in the receiver) the crystal is 455KHz different from the transmitted frequency. You cannot interchange transmitter and receiver crystals.

kistner

My Feedback: (10)

I appreciate all the info. I really need to read up some more. I feel I have a little more understanding but you all have thrown out some terms for me to research (single/dual conversion, shift, etc).
Thanks again

onewasp

Long experience would have me modify your last sentence by placing the period after eBay.

You've obviously been doing some reading but "dual conversion, crystal, 27 and 72 MHz represent obsolete technologies when compared to 2.4GHz.
As you are starting out new why go with the old as I will guarantee you that they are LESS reliable than the 2.4 technology------though you will find a lot of sheer BS on the web that they are not.
When I started RC we were ALL on 26.995MHz.

The new is also VERY reasonably priced.
Your choice, simply additional input-------and unless you are interested in Radio Control history belay reading about dual and single conversion, PCM, PPM, FM etc.

kistner

My Feedback: (10)

I follow you, but my wallet can't go there! over 200 for the 2.4 systems or under 50 for 'obsolete' but functional. These are still just toys for me. I did not spring for a lcd tv or a blueray player yet either; my car doesn't have cruise control; I build my own computers; etc. I guess I'm a little too cheap for new tech/high tech.
But I still appreciate the info
Thank you all

bruce88123

There's cheap and then there is unrealistically cheap. How many planes are you willing to lose due to a system that was thrown together or, worse yet, known to be bad/intermittant so they are selling it off. I strongly suggest staying away from used electronics unless you KNOW the systems history.

kistner

My Feedback: (10)

I drive rc cars, I don't think they'll get too far. I do plan on studying up some more before I buy anything else. And the complete new system, even low end, is looking better to me than the throw together anyhow at this point.