Question in regard to changing Nooelec V1.o from 100 to 125 mhz
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Tony Magon
Nov 24, 2014, 1:45:35 AM11/24/14
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Can anyone advise me if it is possible to change from 100mhz to 125 mhz with the Nooelec V1.0 without any further circuit changes??
73
Tony VK2IC
opendous
Nov 24, 2014, 10:32:40 PM11/24/14
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On the 100MHz version, the -10dB Upconverting bandwidth is 0.1MHz-48MHz (100.1MHz-148MHz upconverted). Replacing the oscillator will reduce that to 0.1MHz-23MHz (125.1MHz-148MHz upconverted).
The other issues is that the LO filter is designed to attenuate the oscillator signal -9.88dB at 100MHz so that it is about +7dBm at the mixer. At 125MHz the attenuation is -25.18dB which will lower the LO signal too much to be usable.
http://code.google.com/p/opendous/source/browse/trunk/Current_Designs/Upconverter/Upconverter_LO_Filter_Testing_Results-VNWA_Data.s2p#1453
http://opendous.googlecode.com/svn/trunk/Current_Designs/Upconverter/Upconverter_LO_Filter_Testing_Results.jpg
If you bypass R3 and R4 (attached pic) it should reduce the LO attenuation enough to be usable but not ideal.
The other issues is that the LO filter is designed to attenuate the oscillator signal -9.88dB at 100MHz so that it is about +7dBm at the mixer. At 125MHz the attenuation is -25.18dB which will lower the LO signal too much to be usable.
http://code.google.com/p/opendous/source/browse/trunk/Current_Designs/Upconverter/Upconverter_LO_Filter_Testing_Results-VNWA_Data.s2p#1453
http://opendous.googlecode.com/svn/trunk/Current_Designs/Upconverter/Upconverter_LO_Filter_Testing_Results.jpg
If you bypass R3 and R4 (attached pic) it should reduce the LO attenuation enough to be usable but not ideal.
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