John, Just move the loops slightly to reduce the insertion loss to 0.5 dB, and recheck the tuning. Keep in mind that the range of a repeater is primarily determined by how well it can hear the distant users, not by how much power the transmitter has. A 1.0 dB decrease in transmitter power should be insignificant, but try 0.5 dB and see how it performs. Please let this group know if the addition of a TX bandpass cavity filter affected the desense problem.
A properly tuned and properly operating transmitter should not be harmed in any way by the addition of a bandpass cavity. 73, Eric Lemmon WB6FLY -----Original Message----- From: [email protected] [mailto:[EMAIL PROTECTED] On Behalf Of John Transue Sent: Wednesday, August 20, 2008 5:16 PM To: [email protected] 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
