Damien, As in most of RF design, the most direct way to an answer is to buy a transformer and try it. My guess, based on the loss that you specify, which is above the minimum necessary for impedance matching, is that the pad is doing other things besides impedance matching. A pad is often used to ensure proper wideband termination of a filter or a ring-diode double balanced mixer. The performance of a lot of those sort of components degrades radically when terminated by a reactive load. The pad may also be aiding the stability of the amplifier following it. It may be necessary to meet a reverse-isolation specification. Nobody likes to give away gain or noise figure by using a pad, but they are often necessary to make the circuit work. If you replace it with the transformer, make sure to thoroughly test the product under all possible conditions, particularly if the pad is the first component in the system... Welcome to the "Black Art" world of RF design, where parasitic effects are always lurking to grab you. Edward Gisske, P.E. Gisske Engineering 608-523-1900 gisske@offex.com ----- Original Message ----- From: "Damien Cahill" To: Sent: Wednesday, April 14, 2004 7:18 PM Subject: [EE]: Impedance Matching. Transformer or Resistive Pad > Hi, > > I am currently updating a cable tv hardware design. The design at present > uses a resistive pad matching device from mini circuits. This is necessary > to match the incoming 75ohm CATV cable to the 50ohm electronics used in the > design. This part is expensive and has an insertion loss of 5.7dB and I'm > pretty sure this type of impedance match can be performed using a wide band > RF transformer such as those manufactured by macom (http://www.macom.com). > In particular I'm considering using the ETC1.5-4 which has 1.5:1 impedance > ratio and is an unbalanced to unbalanced transformer. However before I > proceed I really would appreciate any thoughts the list might have on this > topic as I am only new to this game (3 months) and I don't want to make the > wrong decision. > > > Thanks in advance, > Damien. > > -- > http://www.piclist.com#nomail Going offline? Don't AutoReply us! > email listserv@mitvma.mit.edu with SET PICList DIGEST in the body > -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu