High Level Passive Dbm

The mixer is one of the most important sections in any good- quality SW receiver, since it determines to a large extent the sensitivity and the dynamic range. The so-called switching mixer is often used, because it has none of the technical im- perfections of active mixers. The most commonly found switching mixer is the diode- based double balanced type (DBM), which is, unfortunately, a notoriously expensive compo- nent, especially when a high intercept point is required to ensure low levels of inter- modulation. The application of active devices, such as bipolar tran- sistors and J-FETs, in a passive LO IF primary of Tr2 is 8 turns with a centre tap for the RF input, the secondary is 4 turns. Tr, is wound such that the indicated LO amplitude is available at the secondary. Only the RF input or the IF output requires correct termination on 50 Q, the other connections are then fairly uncritical. The input intercept point of this mixer is excellent at between 31 and 36 dBm, while the...