Scott, John is referring to a single bandpass cavity that he is adding to the TX side of his Motorola 4-can duplexer.
73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of Scott Overstreet Sent: Wednesday, August 20, 2008 8:05 PM To: [email protected] Cc: Scott Overstreet Subject: Re: [Repeater-Builder] Cavity on the TX side First of all---duplexers do get warm in service----your calculations are right on. Now---I think I remember reading that you are trying to use a Motorola 4 section square can duplexer------not enough duplexer for a 90 watt transmitter. And-----a dB duplexer loss on the transmitter path is about right for two cans. Expect 1.5, or a bit more, dB loss or so with a 6 cavity duplexer unless you can find a good Phelps Dodge / Celwave 526 which will give you well better than 100 dB isolation with only a dB of transmitter path loss. Scott ----- Original Message ----- From: John Transue <mailto:[EMAIL PROTECTED]> To: [email protected] <mailto:[email protected]> Sent: Wednesday, August 20, 2008 5:15 PM Subject: [Repeater-Builder] Cavity on the TX side Eric and others, I have re-tuned the cavity to pass the TX frequency. However, it has about 1.0 dB insertion loss at the TX frequency of 448.375. It had about 0.6 dB loss at 443.375. This was of little concern on the RX side. However, on the TX side a 1 dB loss is 18 watts for a PA putting out 90 watts. I don't mind losing this power from going to the duplexer, but is there reason to expect the cavity to fail due to heat or whatever? And if so, how could I protect the repeater and PA from being damaged? Thanks for your sage advice. John
