PA3BZO VHF/UHF HOME

PARABOLIC DISH

AUTO TRACKING BOARD

The options of this extensions are:

 __4 digit digital read out for Azimuth (3 for elevation)
 __Operation of the board with the computer or manual.
 __Great accurate with use of a good digital encoder
 __Also possible for using without the VK3UM.
 __Part list on request via E-MAIL available
 __Software needed for the EPROM is for FREE ! just ask ME
 __This is the same hardware like Darrel VE1ALQ use for the F1EHN system.
     Just other firmware and the possibility to add displays to it. 
 __PCB's are available by VE1ALQ

 __Future plans preset Azimuth direction possibility

COAX cable data

     RG 58 C / U                                         Legend:   a = air dielectric
      |  | |   |__ Cable for general use                           f = foam dielectric
      |  | |______ Issue code, to indicate                         p = poly dielectric
      |  |         variants of original specs                      t = Teflon dielectric
      |  |________ Consecutive number
      |___________ RF Cable
       

Power module data

      Information includes: Type number
                            Working Frequency
                            Class of operation
                            Case model
                            Operating and Bias Voltage
                            Input and Output power

Time Domain Reflectometer

What can you do with this small tool ?

You can use it to find the loose connection in your coax cable or where it is broken.
Simple measuring the length of the coax cable.
Find out what impedance an unknown piece of coax cable has.

What you need for the measuring ?

First of all a pulsgenerator, according this description.
Second you need also an oscilloscope.

The schematic:

The schematic is very simple and straight, the components used are all normal available and inexpensive.
R1, C1 and U3A is a simple oscilatorcircuit that generates a square wave from +/- 500KHz.
R3 and C2 is a variable delay circuit, with C2 you can adjust the proper delay time.
U2B and U2C builds from the output of U3B and U3C a narrow pulse, the pulse width is adjustible with
C2 between 0 and 40 nS. T1 and R4 - R6 generate an output signale from 1 Volt by 50 Ohms.
The circuit runs on 9 - 15 Volt and used about 35mA. The circuit can be build on a small piece of Perfboard.

ADJUST:

This procedure is also simple and straight forward.
Connect the pulsgenerator to your oscilloscope with a BNC "T" adaptor and connect a 50 Ohm load to the
other leg of the BNC "T" adaptor. Turn your oscilloscope to the fastes TIMEBASE possible and turn C2 to
maximum capacitie. Turn now C2 till the figure on your oscilloscope shows the maximum. From this point
you turn backwards till you have reach about 70% of the maximum value. You should see now a needle on
your screen. If your osilloscope has a problem to trigger the signale, you can connect the optinale trigger
output from the pulsgenerator to the extern trigger input of your oscilloscope.

HINTS:

1 meter of coaxcable will give a reflection of about 10 Nano sec.
To measure the impedance, connect one side of the coax to the TDR and the other end with short wires to a
potentiometer. Turn the potentiometer till the reflection disappears on the screen. Now you can measure the
value between the two legs of the potentiometer and you knows the impedance of the coax cable.