Wednesday, February 17, 2010
10.something Mhz FM tx -2
I decided I will finish this 144Mhz transmitter instead of making another pcb to the junk pile.
Have tree choices:
1 - Make a variable modulator in the range 10.2 - 11.2 and mix with 136Mhz (crystal oscillator) to get the desired 144/145 range.
2 - Make a fixed modulator at 10.7Mhz and use the si570 kit to put the frequency on the right spot.
3 - Make a fixed modulator at 10.1Mhz (10.7 - 600Khz repeater shift) and use a cristal oscilator at 136Mhz that can give reception using 10.7Mhz IF and transmitting using the 10.1Mhz IF
Mean while I am placing the tests on a more acceptable board has you can see in the photo.
Since I had none available 10.7Mhz IF transformer I decided to brew one, it's on the bottom right part of the picture, in the left is the coil former type used (can't recall the correct name in English; checked in the dictionary, it's "plastic bushes").
Honestly I still don't know if it works since I spent 1 hour trying to find why the circuit stopped working.....after all it was a broken ground cable at mic input plug.... arrrghhh! Maybe tomorrow I can say more about the homebrew if transformer.