[Repeater-Builder] Re: Desense with Notch-type duplexers - Questions
Hi Dcflux, Yeah, I did that 1st. Actually, they now come out of the front of the box are as far apart as I can get them. Tim --- In Repeater-Builder@yahoogroups.com, DCFluX dcf...@... wrote: Cut the wire tied together TX and RX cables on the back of the quantar and seperate them as far as possible. On Fri, Aug 7, 2009 at 1:43 PM, tahrens301tahr...@... wrote: Hi Folks, Guess it's a good thing the antenna party didn't happen yet. Put the DB-224 up on a pole here attached to a portable building. Ran the 7/8 heliax from the antenna into my garage - about 100'. With a signal source from my monitor, the repeater would chop in and out. Ugh-desense. I am using an old DBproducts 8 cavity notch-type duplexer. 4 on the receive, 4 on the transmit. The transmit side also has stubs. (see old thread). First, I used my spectrum analyzer sweep gen, and got what I thought were pretty good notches in the right places (depending if I was working on the xmit or rx side. According to the analyzer, the notch was about 70dB below the high point. However, I think that it was seeing the floor of the analyzer, not the real notch. Then, I hooked up a signal generator on one side, and a receiver on the other side, and tweaked a bit more for the least signal. All looked pretty good with definite notches, but it's obvious there's desense. All cables are double shielded. The system is 147.10/70, running about 60 watts out of the Quantar. Even running with battery-backup (20 watts), there's still some desense. Could it be that these cans are just not enough, or am I doing something wrong. Thanks! Tim Yahoo! Groups Links
Re: [Repeater-Builder] Re: Desense with Notch-type duplexers - Questions
Yeah, I understand VHF quantars or supseptable to something called 'quantar howl' which is digitally delayed desense. http://www.youtube.com/watch?v=SRfvh0UTFHw The hypnotoad also has the ability to make the same sound http://www.youtube.com/watch?v=kiVYjRbZMe0 I've never owned one so I cant put too many conclusions together about what causes it. I saw the back of one at a ham fest and noticed the wire ties and thought that was the dumbest thing I've seen Motorola do. My next guess could be that the switch mode power supply runs at 600kHz. anyone got any schematics? Also check if you have desense into a dummy load, could be another 600kHz noise source close to your antenna. On Fri, Aug 7, 2009 at 2:11 PM, tahrens301tahr...@swtexas.net wrote: Hi Dcflux, Yeah, I did that 1st. Actually, they now come out of the front of the box are as far apart as I can get them. Tim --- In Repeater-Builder@yahoogroups.com, DCFluX dcf...@... wrote: Cut the wire tied together TX and RX cables on the back of the quantar and seperate them as far as possible. On Fri, Aug 7, 2009 at 1:43 PM, tahrens301tahr...@... wrote: Hi Folks, Guess it's a good thing the antenna party didn't happen yet. Put the DB-224 up on a pole here attached to a portable building. Ran the 7/8 heliax from the antenna into my garage - about 100'. With a signal source from my monitor, the repeater would chop in and out. Ugh-desense. I am using an old DBproducts 8 cavity notch-type duplexer. 4 on the receive, 4 on the transmit. The transmit side also has stubs. (see old thread). First, I used my spectrum analyzer sweep gen, and got what I thought were pretty good notches in the right places (depending if I was working on the xmit or rx side. According to the analyzer, the notch was about 70dB below the high point. However, I think that it was seeing the floor of the analyzer, not the real notch. Then, I hooked up a signal generator on one side, and a receiver on the other side, and tweaked a bit more for the least signal. All looked pretty good with definite notches, but it's obvious there's desense. All cables are double shielded. The system is 147.10/70, running about 60 watts out of the Quantar. Even running with battery-backup (20 watts), there's still some desense. Could it be that these cans are just not enough, or am I doing something wrong. Thanks! Tim Yahoo! Groups Links Yahoo! Groups Links
[Repeater-Builder] Re: Desense with Notch-type duplexers - Questions
I checked it into a dummy load (with one of those celwave signal insertion boxes), and didn't see any signs of desense. A friend of mine who used to work for Mot said that he had a desense problem with a VHF Quantar - Mot sent out some kind of memo that said you had to use some special kind of duplexer. But figured I'd ask around here. Thanks, Tim --- In Repeater-Builder@yahoogroups.com, DCFluX dcf...@... wrote: Yeah, I understand VHF quantars or supseptable to something called 'quantar howl' which is digitally delayed desense. http://www.youtube.com/watch?v=SRfvh0UTFHw The hypnotoad also has the ability to make the same sound http://www.youtube.com/watch?v=kiVYjRbZMe0 I've never owned one so I cant put too many conclusions together about what causes it. I saw the back of one at a ham fest and noticed the wire ties and thought that was the dumbest thing I've seen Motorola do. My next guess could be that the switch mode power supply runs at 600kHz. anyone got any schematics? Also check if you have desense into a dummy load, could be another 600kHz noise source close to your antenna. On Fri, Aug 7, 2009 at 2:11 PM, tahrens301tahr...@... wrote: Hi Dcflux, Yeah, I did that 1st. Actually, they now come out of the front of the box are as far apart as I can get them. Tim --- In Repeater-Builder@yahoogroups.com, DCFluX dcflux@ wrote: Cut the wire tied together TX and RX cables on the back of the quantar and seperate them as far as possible. On Fri, Aug 7, 2009 at 1:43 PM, tahrens301tahrens@ wrote: Hi Folks, Guess it's a good thing the antenna party didn't happen yet. Put the DB-224 up on a pole here attached to a portable building. Ran the 7/8 heliax from the antenna into my garage - about 100'. With a signal source from my monitor, the repeater would chop in and out. Ugh-desense. I am using an old DBproducts 8 cavity notch-type duplexer. 4 on the receive, 4 on the transmit. The transmit side also has stubs. (see old thread). First, I used my spectrum analyzer sweep gen, and got what I thought were pretty good notches in the right places (depending if I was working on the xmit or rx side. According to the analyzer, the notch was about 70dB below the high point. However, I think that it was seeing the floor of the analyzer, not the real notch. Then, I hooked up a signal generator on one side, and a receiver on the other side, and tweaked a bit more for the least signal. All looked pretty good with definite notches, but it's obvious there's desense. All cables are double shielded. The system is 147.10/70, running about 60 watts out of the Quantar. Even running with battery-backup (20 watts), there's still some desense. Could it be that these cans are just not enough, or am I doing something wrong. Thanks! Tim Yahoo! Groups Links Yahoo! Groups Links
Re: [Repeater-Builder] Re: Desense with Notch-type duplexers - Questions
This looks like a good article: http://www.srgclub.org/Desense_testing.html On Fri, Aug 7, 2009 at 2:42 PM, tahrens301tahr...@swtexas.net wrote: I checked it into a dummy load (with one of those celwave signal insertion boxes), and didn't see any signs of desense. A friend of mine who used to work for Mot said that he had a desense problem with a VHF Quantar - Mot sent out some kind of memo that said you had to use some special kind of duplexer. But figured I'd ask around here. Thanks, Tim --- In Repeater-Builder@yahoogroups.com, DCFluX dcf...@... wrote: Yeah, I understand VHF quantars or supseptable to something called 'quantar howl' which is digitally delayed desense. http://www.youtube.com/watch?v=SRfvh0UTFHw The hypnotoad also has the ability to make the same sound http://www.youtube.com/watch?v=kiVYjRbZMe0 I've never owned one so I cant put too many conclusions together about what causes it. I saw the back of one at a ham fest and noticed the wire ties and thought that was the dumbest thing I've seen Motorola do. My next guess could be that the switch mode power supply runs at 600kHz. anyone got any schematics? Also check if you have desense into a dummy load, could be another 600kHz noise source close to your antenna. On Fri, Aug 7, 2009 at 2:11 PM, tahrens301tahr...@... wrote: Hi Dcflux, Yeah, I did that 1st. Actually, they now come out of the front of the box are as far apart as I can get them. Tim --- In Repeater-Builder@yahoogroups.com, DCFluX dcflux@ wrote: Cut the wire tied together TX and RX cables on the back of the quantar and seperate them as far as possible. On Fri, Aug 7, 2009 at 1:43 PM, tahrens301tahrens@ wrote: Hi Folks, Guess it's a good thing the antenna party didn't happen yet. Put the DB-224 up on a pole here attached to a portable building. Ran the 7/8 heliax from the antenna into my garage - about 100'. With a signal source from my monitor, the repeater would chop in and out. Ugh-desense. I am using an old DBproducts 8 cavity notch-type duplexer. 4 on the receive, 4 on the transmit. The transmit side also has stubs. (see old thread). First, I used my spectrum analyzer sweep gen, and got what I thought were pretty good notches in the right places (depending if I was working on the xmit or rx side. According to the analyzer, the notch was about 70dB below the high point. However, I think that it was seeing the floor of the analyzer, not the real notch. Then, I hooked up a signal generator on one side, and a receiver on the other side, and tweaked a bit more for the least signal. All looked pretty good with definite notches, but it's obvious there's desense. All cables are double shielded. The system is 147.10/70, running about 60 watts out of the Quantar. Even running with battery-backup (20 watts), there's still some desense. Could it be that these cans are just not enough, or am I doing something wrong. Thanks! Tim Yahoo! Groups Links Yahoo! Groups Links Yahoo! Groups Links
[Repeater-Builder] Re: Desense with Notch-type duplexers - Questions
Hmmm, Well, I did the signal injection into the receiver's port, as opposed to at the dummy load, and indeed, I do have desense when using the dummy load. I guess that points back to the cans how well they are performing (or not)!
