Dots on JR crystals
02-07-2007, 09:26 PM
#2
RE: Dots on JR crystals
wpbeyes,
From JR FAQ's:
What do the dots on the crystals mean? Are they important?
The dot indicates the cut of the crystal in relation to its true frequency, either centered exactly on the frequency or just above or below the frequency when viewed on a scope. With today's level of tuning, it makes very little difference in overall performance. For top performance, in those models that require the absolute best, such as turbines and giant scale aircraft, avoid using oposite dots in the transmitter and receiver, such as a left dot in the transmitter and a right dot in the receiver. For the best performance they should be next to each other, a center and a right or left, or the same. The dot system is a way that JR users can fine tune their set up for optimum performance.
Also, search this forum for 'dots' and you'll find more info from Danny.
Regards,
John
From JR FAQ's:
What do the dots on the crystals mean? Are they important?
The dot indicates the cut of the crystal in relation to its true frequency, either centered exactly on the frequency or just above or below the frequency when viewed on a scope. With today's level of tuning, it makes very little difference in overall performance. For top performance, in those models that require the absolute best, such as turbines and giant scale aircraft, avoid using oposite dots in the transmitter and receiver, such as a left dot in the transmitter and a right dot in the receiver. For the best performance they should be next to each other, a center and a right or left, or the same. The dot system is a way that JR users can fine tune their set up for optimum performance.
Also, search this forum for 'dots' and you'll find more info from Danny.
Regards,
John
02-08-2007, 08:41 AM
#3
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RE: Dots on JR crystals
To fully understand the reason behind the need to use crystals that is slightly “off frequency†one must first understand more about the system. RC radios that use FM modulation do not modulate (shift frequency) positive and negative from the center frequency like a normal FM two-way radio. They shift only positive or only negative, JR radios have positive shift. This means that in a normal frequency channel you are using only half of the channel (half of 8 KHZ). If you were to shift the frequency of the crystal 2 KHZ negative (dot to the left) the part that you would be utilizing will be in the middle of your channel and you will now be 3 KHZ from the channel above you instead of 1 KHz. Although JR uses good quality band pass filters, no filter is perfect and they will be somewhat less sensitive at the band edges, so if you can keep your business in the center you should have better sensitivity, less chance of interference and less chance of interfering with the channel above you( if you using a JR radio). I wonder if it is possible to get any of these types of crystals for 35MHz?
