I just got a UHF Expo VRS SP02 and I can't figure out what the recieve frequency is for the VRS. It will transmit fine on 457.215 or .220 but, I can't figure out the recieve. I have the crystal frequencies.
They are the following:
5011527, with a green stripe over it
5075468 with a red stripe over it
I'm assuming the red and green stripes are for tx/rx but, I'm not sure I've never messed around with a crystal radio before. Any help would be appreciated. Thanks
VRS crystal calculation help
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Not always...
I had one of the Expo based VRS units and the TX and RX were totally different on purpose for some reason..
If i had to guess i would say it's because they didn't want a seperate simplex channel programmed into everyone's portable, so they just made the VRS opposite of one of the duplex channels they had in the portable.
But anyway, yes, its a good chance they are the same.
I had one of the Expo based VRS units and the TX and RX were totally different on purpose for some reason..
If i had to guess i would say it's because they didn't want a seperate simplex channel programmed into everyone's portable, so they just made the VRS opposite of one of the duplex channels they had in the portable.
But anyway, yes, its a good chance they are the same.
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"I Reject Your Reality And Substitute My Own!" - Adam Savage
Thanks kb0nly, I was able to figure out that the 457.2125 was a harmonic frequency coming off of my vhf portable. The real frequency is 451.0375 and it is simplex. But, now I've discovered I have a cold joint somewhere on the board. When I press down on one of the potentiometer's I get audio repeated from the mobile and when I let go it stops repeating the audio even when there is traffic on the channel. I've also discovered I can't key up the vrs either. Guess I'll call up the Moto shop nearby and see if they can service it. Thanks again.
Stu
I think the color stripes indicate the temperature coefficient of the crystal. UHF portables require the correct compensation characteristics to be able to stay on frequency for a reasonable length of time (they are overtone crystals that work on harmonics). If you order crystals from one of the long time manufacturers they will have the information on file to provide the correct crystals for your Expo. All you will need is the frequency. Be aware the Expo uses an extra receive crystal for the 455 KHz IF conversion. For some reason Motorola recommend using one of two different frequencies (one using + injection or the other using – injection) depending on the receive frequency. The Expo or RNET manual has the frequency table. If you do it by the book for a single frequency Expo you need one or two receive crystals (the second depends on if the one you have is already the correct one for your Rx frequency) and one Tx crystal. On the other hand I never figured out why they swapped the IF injection in the first place?