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View Full Version : FM25B tuning range & TP1 voltage


dsmithx
03-08-2002, 05:46 PM
Hi,

I've sucessfully put the kit together but have some funny behavior on the tuning range. The voltage at TP1 is at 9V at 107.9Mhz. When I adjust the frequency down it locks at each setting, down to about 89 Mhz, with correspondingly lower voltages each time. It won't lock at 88.1 Mhz, even though the voltage at TP1 is at 0.7 V. When I adjust L1 to obtain a higher voltage, say around 2.3 V, then it locks but won't lock at higher frequencies because the voltage is off.

I'm fine with not being able transmit at 88.1 but will this behavior of the circuit affect stability or other operation in some way?

David Smith

Chris Hughes
03-11-2002, 07:33 AM
Hi David!

Take a look at the height of the installed components in the oscillator section (near L1) of the kit. If they are not flush with the circuit board (within reason of course) then the added inductance of the extra component leads will affect your tuning range.

The other thing to quickly double-check is the value of all the components in the oscillator section. Make certain none of your parts were accidentally switched.

I know these may seem basic, but they are the most common faults we see.