Tuesday, October 27, 2009

VHF FM receiver with Si570 VFO

Now I have two receivers working in sync with the same VFO, the airband receiver and a VHF FM receiver based on the NE602/MC3361 combination, they have separate antennas but a common audio amplifier.
The MC3361 circuit is based on the one at: http://f6feo.homebuilder.free.fr/RX_LA1185.html
I just replaced the TA7358 front end for an NE602 front end similar to the one on his datasheet. The 10.7 filter is a salvage unit from a chinese store radio.
Unfortunately the squelch is not fully operational and I will have to check again the schematic against the datasheet.

Here working simultaneously with the AM part of the circuit:

As soon as I build the other Si570 kit that arrived probably will place it in another box and not in the airband receiver box. Initialy my idea was to make an coil vfo for the NE602 but since I have the Si570 it will stay more acurate and frequency stable. Tried to replace the discriminator coil for an 455Khz ceramic cristal but didn't worked good, will try one of this days a combination of an commercial inductor and a capacitor since discriminator coils are not the easy thing to get around town. Probably an 360 microH with an 340 Pf capacitor will ressonate at 455Khz.

1 comment:

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