If I could afford that equipment I would do that. However the thought of spending as much on test equipment as a new car is a little tough.
We do have a service monitor in the group I hang out with but it does not have a tracking generator. Vern On Tue, 16 Oct 2007 11:15:11 -0600 Nate Duehr <[EMAIL PROTECTED]> wrote: > [EMAIL PROTECTED] wrote: >> Well the local ham fest rolled into town last weekend >>and >> I was able to get some cans. One of which is a DB >> products bp can model sp6610C. A friend tuned it up for >> me and I put it between the MASTRII on the receive side >> and the receive side of the db4048 duplexer that I have >> which wasn't providing proper isolation. It's like I >>have >> a new repeater. I have not been able to do any extended >> testing yet but I can run lower power on my mobile >>around >> town then before and people on HTs that couldn't hit the >> machine from in their house can now do so full quieting. > > Now if you want to take the next step, and go from a >"thinking" man to a > "knowing" man... > > Use an Iso-T or directional coupler, and a signal >generator on your > input frequency and some way to measure the 12dB SINAD >point of the > receiver. > > (If you're using a service monitor, they'll usually do >both the signal > generation at an accurate power level, and the SINAD >measurement, but > you can also use a much cheaper standalone signal >generator and > something like a Sinadder S/N measurement device.) > > Measure the real-world receiver sensitivity numbers, put >them in the > engineering logbook, and track it over time. It allows >for a lot of > things, like knowing if your receiver suddenly has "gone >deaf", etc. > Also allows you to track it over time to see if you have >a slow > degradation going on, site noise going up, etc. > > While you're set up to do that test, desense is easy to >test for, too. > > Inject a weak signal into the receiver and set it to the >"noisy" 12 dB > SINAD point, with the repeater transmitter off. Turn >transmitter on. > > If weak signal disappears or gets noisy, you don't have >enough > isolation, you have leaky interconnect cables, or >something else is > wrong... you have desense. A properly working system >should have none. > None at all. You should hear no difference at all with >the > transmitter on or off. > > If you have desense, leave the transmitter on, and turn >the signal > generator up until you're back to 12 dB SINAD. Now you >know how much > the power level had to change to get back to your >arbitrary reference > point, and therefore, you know how many dB of desense >your system is > experiencing, so you have hard numbers as to how bad the >desense is. > > Then you can share here on the list, and folks that have >used the type > of radio and setup you've built -- can tell you if >that's what they > would expect to see from your specific radio type, etc. > > If you get in the habit of doing these tests at least >once a year on > established systems, and/or during an installation of a >new system, and > recording all the numbers -- you then know right away >that the system > isn't performing as well as it should, opposed to >finding out by > "shotgunning" in more filtering later on. > > Knowing up-front is nicer, once you get in the habit of >going through > the extra (minor) work of doing the real tests. > > Nate WY0X
