RNet 450 XTAL Calc

[hoser]

Anyone have the service manual or the calculation to determine the crystal frequencies for this unit?

[kc7gr]

Anyone have the service manual or the calculation to determine the crystal frequencies for this unit?

The formula differs a bit depending on which split you have.

If you have a UHF RNet unit covering from 403-433MHz, the crystal frequency formula is Fxtal = (Fcarrier - 45MHz)/7.

If it's a 450-470 unit (and I know from personal experience that they'll go down to at least 446 with no problem), the formula is:

Fxtal = (Fcarrier - 45MHz)/8.

I hope that helps. Happy tweaking.

[hoser]

Thanks very much! The unit is a 450 Model with Tx=Rx=464.5000MHz

The formula for the 450 model works since the top of one of the xtals reads '52437500' which is obviously 52.4375MHz. This one is closest to the BNC connector and has a part # of KXN6331.

But...........

The other xtal (furthest away from the RF output BNC) has '17203703' printed on its top? Its a Motorola part # KXN6330

Whats the deal with this other xtal? ANy ideas?

[kc7gr]

Thanks very much! The unit is a 450 Model with Tx=Rx=464.5000MHz

The formula for the 450 model works since the top of one of the xtals reads '52437500' which is obviously 52.4375MHz. This one is closest to the BNC connector and has a part # of KXN6331.

But...........

The other xtal (furthest away from the RF output BNC) has '17203703' printed on its top? Its a Motorola part # KXN6330

Whats the deal with this other xtal? ANy ideas?

Sure. That's your transmit crystal. The transmitter and receiver have separate crystals. This is The Way It Works for nearly all crystal-controlled land/mobile (and most old amateur) FM transceivers.

In fact, I have to apologize. The formula I gave you was for the RECEIVE side only. The transmit side formula is Fcarrier = Fxtal * 27.

If you take 17.203703 MHz, and multiply it by 27, it comes out within a hair of 464.500 MHz.

FWIW: International Crystal can supply you with replacement crystals for any frequency you wish for about $40 plus shipping, total. I would also strongly recommend that you purchase the RNet service manual, Motorola part #68-80901Z35.

Happy tweaking.