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Lower Gain on CDMA VCO
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Lower Gain on CDMA VCO

by sciguy14 on Mon Aug 10, 2009 10:23 am

So I'm having issues with my wavebubbles. On both of them the 800MHz VCO performs much worse. Upon hooking up to a fast oscilloscope, I can indeed see that the amplitude of the GMA VCO is about 10 times larger than that of the CDMA VCO. Any ideas what would cause this on multiple boards? Which resistor or capcitor value would be most important for me to look at changing?
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Re: Lower Gain on CDMA VCO

by Buggy222 on Tue Aug 11, 2009 3:17 pm

I am sure there are others on this board who can suggest more than me, but since I am in the middle of similar problems I will suggest a few things.

If you program the wavebubble to test the VCO's, you should see a voltage range on the input to the VCO's which should be set to cover the voltage range of the VCO's you are using. The 2500+ has a range of 1 - 11 volts with a max of 16, and the 1700+ has a range of 1 - 24 volts with a max of 30. During this test your scope should show the input ranging, then setting midrange and the bandwidth being scanned which for me was a width of about 3 volts. The bandwidth gain is the same as the VCO voltage gain, so it will vary between the VCO's. Resistors R13/14/15 and 16 are used to control the VCO input gain.

Next check that the VCO is getting 11 volts on its Vcc input.

I think that the CDMA Ev VCO is the 2500, and the GSM VCO and CDMA 1X is the 1700. At least this is what I seem to be finding in my Sprint/Verizon area.

Is your PLL tuning and not giving you a error?
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Re: Lower Gain on CDMA VCO

by sciguy14 on Tue Aug 11, 2009 3:31 pm

Thanks for the ideas.

I originally had trouble with the PLLs tuning, but I found that after I added further components, it started to tune consistently.
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Joined: Fri Jun 12, 2009 3:19 pm

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