Rick, You might check to see if the internal jumpers inside the VXR-7000 cabinet are single-shielded. I had a VXR-5000 UHF repeater that had single-shield jumpers with gray jackets and no markings, and had a small amount of desense. Once I replaced all three jumpers with RG-400/U double-shielded cable, there was no trace of desense. Perhaps Vertex tried the same money-saving trick on the later model. Check to make sure that all shields and cover plates are installed, with no screws missing.
I wonder if your duplexer has been mis-identified. A DB4026 is a UHF bandpass cavity filter, not a duplexer. You probably meant DB4062, which is a six-cavity VHF BpBr duplexer. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of pontotochs Sent: Wednesday, December 17, 2008 2:04 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] VXR 7000 with desense Hi, I've checked the previous posts on this issue, but I am hoping that there is more light to be shed. We have a VXR 7000 that has had issues for a while as a two meter repeater. In the shop we set it up with its DB 4026 duplexer and 50 ohm dummy load and monitored the output power with a Bird thru line watt meter. We used a service monitor to inject the RX signal to get 10 dB quieting (approx 0.2 micro volt). Put the unit into repeat mode and the repeater will cycle (go in and out of transmit) until the RX signal is increased about 20 to 25 dB (approx 3.6 micro volt). Looking at what is coming in the receive port with the transmitter is keyed is about -75 dBw (50 watt out with about 95 dB of isolation) at the TX frequency, and there is little to no hash at the RX frequency - seeing the noise floor of the spectrum analyzer (-120 dB). Put the 7000 into base station mode, hooked up second signal source, set first signal source to give 10 dB quieting at the RX frequency (0.2 uV), set the second signal source to emulate what we saw from the duplexer (79 mV at TX frequency) and there was no desense. Increased the simulated TX voltage to better than 1 volt and still no desense. My thought is that something has gone bad internally within the 7000. Is there something else I need to try? Thanks in advance for your help. Regards, Rick, N5RB
