This looks like a good article: http://www.srgclub.org/Desense_testing.html
On Fri, Aug 7, 2009 at 2:42 PM, tahrens301<[email protected]> 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 [email protected], 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, tahrens301<tahr...@...> 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 [email protected], 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, tahrens301<tahrens@> 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 > > > >
