Re: [Repeater-Builder] VXR 7000 with desense
Hi Rick -- I am new to the group so I have not seen all of the posts with regards to your problem on the 7000. However, one thing that you may want to check is whether the PL is feeding back into the RX from the TX, if the tones are the same. I have seen this several times in the past on different machines and it is always annoying. Don't assume that just because you can run PL in and out that it will be able to run the same tone. GL -- Rick NU7Z On Thu, Dec 18, 2008 at 9:44 AM, Doug Bade k...@thebades.net wrote: Rick; I think you need to isolate whether it is tx through the duplexer or something else bothering the rx and or squelch. It sounds like the tx signal fundamentally is clean from your analysis so far.. in order to isolate through the duplexer, connect the tx directly to a dummy load instead of it's side of the duplexer while injecting rx into the duplexer. if it does not cycle, the tx is sending something through the duplexer to the rxif it does cycle.. it is an internal issue as you suspect.. I would use the tx to duplexer cable in the dummy load path as you want to see if some radiation from it is part of the equation. I lean more to spurious on initial keyup... causing a noise burst maybe due to exciter tuning... but this test should tell you if it is conducted internally or passed through the duplexer. Doug KD8B At 05:04 PM 12/17/2008, you wrote: 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
Re: [Repeater-Builder] VXR 7000 with desense
At 12/18/2008 10:02, you wrote: Hi Rick -- I am new to the group so I have not seen all of the posts with regards to your problem on the 7000. However, one thing that you may want to check is whether the PL is feeding back into the RX from the TX, if the tones are the same. I have seen this several times in the past on different machines and it is always annoying. Don't assume that just because you can run PL in and out that it will be able to run the same tone. Why not? If something is mixing the output back to the input, normally you'd want to find eliminate it since it's necessarily causing desense. Running different or split tones, can serve to cover up the problem if it's external to your equipment and out of your control. However, most ham transceivers are not capable of split tone operation. Bob NO6B
[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
Re: [Repeater-Builder] VXR 7000 with desense
Rick; I think you need to isolate whether it is tx through the duplexer or something else bothering the rx and or squelch. It sounds like the tx signal fundamentally is clean from your analysis so far.. in order to isolate through the duplexer, connect the tx directly to a dummy load instead of it's side of the duplexer while injecting rx into the duplexer. if it does not cycle, the tx is sending something through the duplexer to the rxif it does cycle.. it is an internal issue as you suspect.. I would use the tx to duplexer cable in the dummy load path as you want to see if some radiation from it is part of the equation. I lean more to spurious on initial keyup... causing a noise burst maybe due to exciter tuning... but this test should tell you if it is conducted internally or passed through the duplexer. Doug KD8B At 05:04 PM 12/17/2008, you wrote: 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
RE: [Repeater-Builder] VXR 7000 with desense
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
Re: [Repeater-Builder] VXR 7000 with desense
I don't know what type of service monitor you are using, but I tend to use an iso-tee to measure desense with the duplexer hooked to a dummy load through the iso-tee. It might be possible for the service monitor to contribute to some signal reflection if it is used as the power termination. Make sure the cables to the duplexer are double shielded, like RG-214, and inspect the connectors to make sure all the grounds are in good shape. Check the internal cables in the VXR-7000 for the same potential problems. I may be preaching to the choir and if so I apologize. 73 - Jim W5ZIT --- On Wed, 12/17/08, pontotochs pontoto...@bellsouth.net wrote: From: pontotochs pontoto...@bellsouth.net Subject: [Repeater-Builder] VXR 7000 with desense To: Repeater-Builder@yahoogroups.com Date: Wednesday, December 17, 2008, 4:04 PM 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
