Tag fixed. I am really tired with OE screwing with the tag. ----- Original Message ----- From: "Edward Gisske" To: "pic microcontroller discussion list" Sent: Thursday, April 15, 2004 7:44 AM Subject: Re: Impedance Matching. Transformer or Resistive Pad > 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