[Music] okay today I'm going to demonstrate how to do a distance default test and what I have is a test transmission system consisting of an antenna I have six feet of jumper I have approximately 33 feet of LDF 550 a transmission line and then I also have another six foot jumper connected to my test cable very important to have a diagram of your system so you know exactly what's in it so when you're doing a distance default test you want to set up your frequency range and I have mine set up from 700 megahertz to
1100 megahertz we generally go a little bit wider than what our system frequency is then I need to set up some distance default information and you would press the DTF icon and this menu will show up so I'm going to change my units to feet I'm going to set my Stu my start start distance is at zero I want to set my stop distance well if you remember I've got a six foot jumper 33 foot of cable another six foot jumper and two or three feet of antenna so that comes up to approximately 45 feet
I want to add about ten or twenty percent on the end of my distance to full so I'm going to set my stop distance to sixty feet I need to select my table because there's two components of table information we need which would be the velocity and the cable loss so I'm going to scroll through the cable list until I get to LDF 558 and that's going to populate my disk my table parameters at 89% velocity and point oh 1 to 6 DB of loss per foot so I have my table information set up the
other thing I want to select are my data points the more data points the more resolution you get the further into a table you can see so I have my table information so I have all the information I need for my sweet so what I'm going to do is very important that you calibrate the instrument anytime you make a change to the frequency anytime you change into your distance to fold information you need to calibrate always look for this correction on but to be safe I'm just going to you know with Mikan my correction is
still on but just to be safe I'm going to go ahead and recalibrate it only takes a second I'm going to calibrate out to the end of my test cable so it removes this from the measurement do the open and do the short and then I do the low now I know I have a good calibration and now I'm going to connect up into my antenna system I'm off the screen a little bit with my sweep so I'm going to go ahead and adjust my scale I'll set my top scale to zero and set my
bottom scale to minus 70 and what I'm going to do is use some markers so I have a marker on and I want to go to the max peak which is right here and I'm very very close to zero at about 39 feet well if you remember I have a 6 foot jumper 33 foot of transmission line another 6 foot jumper in my antenna so if I was looking at my antenna I would be out somewhere at around 45 feet possibly actually about 40 18 but I have a problem out here at 39 feet so
that's going to require me to go out and inspect so 39 feet comes to the beginning of my top jumper and it shows me that I do not have a center pin in my cable so I have a bad cable so that needs to be replaced and just to verify where the end of my transmission line is if I come out here and install a load a precision 50 ohm load my marker is right there at 39 feet and I'm down at about negative II if I remove the load and connect and open or leave
it open but notice how this comes up to about zero DB so that is the end of my transmission line so if I replace my jumper and connect it to my antenna here's my connector out at 39 feet which was where the end of the cable is I did not move that marker I'm going to add another marker and I'm going to put that at about oh let's say 45 feet so if 45 feet which is the connection going into my antenna that would be this connector and I can add one more marker and put
it at about 48 feet and right there is where my antenna is just below the neg 14 DB limit line there are a couple other Peaks here right out there and I'm going to guess if I add another marker and set that to about 6 feet marker 4 is at 6 feet I'm at negative 32 dB my first connection at the top of the first jump or where it goes into my transmission line you
