Gary,
At this juncture, I'm not getting scientific about the actual desense measurement, but I can tell you it's in the ten's of dBs. At this point, I'm using Kevin's method. signal generator connected to the cans with the cans connected to the repeater normally. I set the signal generator to the point that the squelch breaks and turn the transmitter on manually. If the signal stays there. I'm happy (at this point). If not. I increase signal generator level until I keep the signal with the transmitter on. As I said. it's ten's of dBs at this point You're correct about where I'm connecting the dummy load. Again. I'm not using ANY antennas at this point. All testing is done into the -8920 and/or the dummy load. I'm confused about your last statement. I've not put a load at the end of the tee that feeds the feedline. If I do that, I can't feed signal to the receiver. If I take the TX line off the tee and put a dummy load there, there is no desense. Mike WM4B From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Gary Schafer Sent: Tuesday, October 07, 2008 8:54 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Desense has me pulling my hair out! (Was DB4060 Duplexer Cables Mike, How are you measuring the desense? How are you connecting the signal generator to the receiver? What are you using for an indicator of sensitivity on the receiver, sinad, quieting etc? I am assuming that you are replacing the antenna line with a dummy load at the output junction on the duplexer when you say that you "tried a dummy load on the system" and you get no desense that way. Have you also tried with the antenna still connected to the output of the duplexer and the dummy load connected to the receiver input (receiver disconnected from the duplexer)? If you have no desense with a dummy load on the output of the duplexer then you do not have a duplexer problem. Let us know how you have done the above. 73 Gary K4FMX _____ From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Mike Besemer (WM4B) Sent: Tuesday, October 07, 2008 5:03 AM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Desense has me pulling my hair out! (Was DB4060 Duplexer Cables With the tee connector split and the TX side going into a dummy load, there is no desense. If I reconnect the tee and go to the -8920, the desense is back. The tee's are MILSPEC connectors. same ones that have always been on there. Unless something catastrophic happened, I don't THINK any of them are bad. Thanks for the suggestions though. I'm running on empty. Mike WM4B From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of DCFluX Sent: Tuesday, October 07, 2008 2:21 AM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] Desense has me pulling my hair out! (Was DB4060 Duplexer Cables I don't know if you have tried this or not, but do you have desense with the duplexer into a dummy load? Or does it just show up when you hook up an antenna? Switch mode power supplies are famous for putting out noise on 600kHz, such as found in battery chargers in boats and RVs. We recently had a problem in the area with 'The Beast' desenseing a .94 box. It turned out to be the site owners son's electric shaver charger. If this is true you only get desense when the repeater is transmitting, but it will appear on both the + and - offsets. To find the source of the problem walk around the area with an AM radio on 600kHz, or some fox hunting gear on the repeaters input. Turn down the power output of the repeater so you don't false the hand held but still have desense. Other things to look at: If I remember right this cavity has removable loops, check the solder joints between the connector and the loop and the loop to the capacitor. Your tee's may also hold some truth to the mystery, If you can not verify whom manufactured them you may wish to examine one by cutting it open with a dremmel. Some times people 'borrow' a good connector or tee and replace it with el-cheapo trucker's choice made in china goodness, of which you cut open and find steel springs.
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