Lets not get carried away here; making statements like "The 1N4007 is actually a PIN diode. However, the lower-voltage siblings in the 1N400x family are not - use ONLY 1N4007." Are simply wrong and cannot be substantiated. This is the kind of misinformation that sets "hammy-hambone" apart from hombrewers, who are into amateur radio. Here is the datasheet... http://www.vishay.com/docs/88503/1n4001.pdf Truthfully I wouldn't caught dead using one of these as a PIN diode, maybe a varicap, even the range is limited and the linearity is garbage. Any diode will work to an extent as a pin diode. This diode family has too much junction capacitance to be all that useful as a PIN diode even at HF. There are better alternatives. Be careful of the advice that is out here on the Zed, some sources are more reliable than others.