On Sun, 6 Jan 2008 22:32:40 -0500 "Sean Breheny" wrote: > I have a very low-level (microvolt) audio source with a 50 ohm > impedance (it is a diode mixer in a direct conversion receiver). I > also have an audio amplifier which has a gain of about 10000 in > voltage, 5 uV input noise, flat audio response down to about 10Hz, and > a differential audio input with a 10K impedance. If the receiver is for shortwave, you wouldn't want to worry too much about low-end audio or any quality at all (no one modulates below, say 300Hz). Also, you will probably have enough (atmospheric) noise not to bother with audio impedance adapting. Just put a 50 Ohm resistor as terminator and connect the audio amp. On the other hand, at VHF or UHF frequencies, as far as I know, no USB (or maybe AM. if the LO is synced) is used. So I'm not sure what modulation you'd want to receive from a DC receiver? John -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist