HOW TO CHANGE THE OUTPUT CHANNEL OF T-93 CONVERTERS
both the input and output channels of a t93 converter are normally factory preset.
the input channel filter has to be adjusted in the factory because of its complexity:it requires specialised and expensive equipment that surpass the limits of most installers.
the output channel is not filtered so that it can be changed.
to change the output channel, proceed as follows:
- inside the unit there are two blocks of dip-switches that can be set for a particular binary code in accordance with the difference between both input and output channel frequencies.
- verify that the channel conversion is possible by checking the annexed channel incompatibility tables (blank when compatible, a crossed when incompatible and circled whenever it is possible but not recommended).
- if they are compatible, open the unit to have access to the dip-switches as well as to the local oscillator control jumpers j1 to j6 (see figure).
fo= output channel video frequency
fi = input channel video frequency
flo = local oscillator frequency
flo = fi - fo=>this value is expressed as dpv in the annexed table no. ii
look for this value in the appropriate column and record the correspondent binary code to be set in the dip-switch blocks inside the unit.
- the local oscillator selection is the next step that is needed to achieve the desired output channel.
the unit has two local oscillators that have to be adequately combined to obtain the flo calculated
to do this, check the annexed table no. i and look for the combination of jumpers, j1 to j6, that suit the calculated flo.
- position the binary code recorded in the two blocks of dip-switches sw1 and sw2. (see nex picture to located them on the pcb).
remark:remember that this converter does not have output filter since it was designed to be connected to a single channel amplifier.
never use it with a broadband amplifier unless you have filtered its output.
let us suppose the following data:
- input channel no. 40 (video frequency: 623.25 mhz)
- output channel no.6 (video frequency: 182.5 mhz)
- in the channel compatibility tables, it is possible to check the possibility of the conversion. otherwise, nothing can be done and another output channel must be chosen.
- flo = 623.25 – 182.25 = 441 mhz
for this value dpv=441 look in the table no. ii the corresponding binary codes
table no. ii
dpv = 441
the binary code is:
1101 for block sw1,
10001001 for block sw2
because 441 is not between 490 and 890 (see table i), we will only set the jumpers controlling local oscillator no. 2.
441 is between 250 and 490, so the jumpers have to be positioned as follows:
j1 => off
j2 => on
j3 => 2
j4 => 2
j5 => off
j6 => on
- the output channel has to be channel no. 6