RME-29 Receiver and DB-20 Preselector - Image Rejection

RME manufactured the DB-20 preselector as an accessory to the RME-69 receiver. This was to provide an additional 20dB of gain and improve the image frequency rejection, especially on the higher shortwave bands where the separation of wanted and image frequencies provided by the 465KHz IF frequency is close enough that the single RF amplifier and two tuned circuits at the tuned frequency gave poor image frequency rejection. This video provides a (crude) measurement of the RME-69 image rejection at 25MHz of (-12dB). At the same frequency, the addition of the DB-20 preselector resulted in an image frequency rejection of around -25dB. Also, the claimed 20dB gain of the DB-20 is confirmed, though some additional noise is also introduced when the preselector is in circuit

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