Image Noise - VHFUHF Forum at eHam.net

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eHam.net Forum : VHFUHF : Image Noise

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Image Noise	Reply
by K5MBV on October 18, 2009	Mail this to a friend!
There seems to be very little attention paid to image rejection where microwave downconverter circuits are discussed and construction articles are published. Since noise added by the image using wide band LNA circuits can be 3 dB (or greater if there are signals in the image frequency) it seems like that this much noise would be worth eliminating. 3dB additional noise is a lot at microwave frequencies and that much improvement in MDS would require doubling the antenna gain. Is image rejection too expensive or too complicated to add to low noise amplifiers and downconverter inputs?

RE: Image Noise	Reply
by WX7G on October 23, 2009	Mail this to a friend!
Image rejection at the RX input can be achieved with a band pass filter. However, the mixer will still convert the thermal noise at the image frequency.

RE: Image Noise	Reply
by K5MBV on October 25, 2009	Mail this to a friend!
I would expect that a filter which would reject the image would reject everything on the image frequency: noise and all by the same amount. Ken K5MBV

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