This file upload is cool....
This morning here I converted my Quadrature Phase Mixer into a fully
working Quadrature Phase Modulator. With separately modulated (I/Q)
carrier outputs, combined into a single carrier for transmitter use.
I have uploaded the file here for you to run in LTspice.
http://groups.yahoo.com/group/soft_radio/files/SDR%20Spice%20Analysis%20Files/Quadrature_Phase_Modulator.zip
The two mixers, mix a carrier of 10 MHz together with a 90 degree
phased pair I/Q running at 12 kHz and hence, is being modulated from
in the baseband audio range.
The I/Q is then mixed together at the end into T1 which is a 1:1
balun, and emerges as one 12 kHz modulated, 10 MHz carrier at the output.
T1 in this case is theoretical with a coupling of 1 and so you can do
what you want with it.
I have the input levels adjusted so that you can see the effect of the
two phase shifted 12 kHz modulation sources on the combined carrier at
output to make the effects of phased modulation look clearer to you.
If you look carefully at the upper and lower peak of each modulation
burst. You will see the the upper and lower peaks are shifted 90
degrees. You might at first mistake them for being 180 degrees apart
in peak to peak amplitude.
You can adjust the input levels so that the carrier looks more like a
AM modulated carrier.
In this circuit the 20 MHz harmonic is down -51 dB.
Dannie Jackson
ka9rza
1/Mar/2008 10:05
