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As noted in this photo, single-conversion receivers have one crystal, while dual-conversion receivers have two crystals. The one labeled “IF crystal No. 2” in this photo is soldered in place, so obviously it is not the one intended to be swapped. |
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Here Bob is running a simulated range-verification test at the flying field. Every time you swap a receiver crystal you are advised to run this test since changing the crystal may have also changed the receiver’s tuning. |
Q-34: I understand that it is simple to change the operating channel (frequency) of any RC receiver by just swapping the crystal. Is it really that simple? Some of my friends have told me not to do this!
A-34: Swapping receiver crystals can be done if you follow some established rules. First, you should restrict yourself to only using crystals from the same manufacturer. Certain cases exist where one brand of crystal will work in another brand receiver, but there are so many exceptions to this. I advise you to use only the same brand of crystals.
The next consideration is the type of receiver. There are single-conversion and dual-conversion RC receivers on the market. Some manufacturers actually offer both types. Within a given brand of receiver, you still must know if it is of dual-conversion or single-conversion circuitry.
There is a difference in the kind of crystal employed in both types. Trying to place a crystal intended for a single-conversion receiver into a dual-conversion receiver will not work. To identify your receiver's type, look for the words "dual conversion" on the outside of the receiver case. You can also tell by opening the receiver case. A dual-conversion RC receiver will have two crystals, while a single-conversion receiver has only one.
If you do change the crystal in a dual-conversion receiver, you should be concerned with the crystal that is easily accessible from the outside of the case. The intermediate-frequency crystal (the second crystal) in a dual-conversion receiver is usually soldered in place.
Let me go just a little farther. I do swap receiver crystals quite often because I own two synthesized RC transmitters where I can literally "dial up" any one of 50 RC channels available for model aircraft use. When I do shift a channel (frequency), I try to stay within the same area of the band. If I’m using CH-47 and need to change, I will try CH-48, 49, 46 or 45. In other words, I will stay in the same area.
Some receivers are tuned for the center of the band; others may be tuned to the middle of the lower half and the middle of the upper half of the band. Any way you look at this scenario, you should not be going from CH-11 on one end to CH-60 on the other.
What may be in tune on one end, may not be on the other. My final suggestion after changing a receiver crystal is to always perform a range-verification test with your transmitter antenna collapsed (or retracted) before flying. If you are unable to obtain the manufacturer's recommended range (usually 50 to 100 feet), something is not right. It is likely your receiver is out of tune with the new crystal you just installed.