Global Microwave Systems Inc. M2T-D3 Manual De Usuario
100-M0113X1 Rev. 04-17-09 PAGE 36 OF 41
9.0 D/C (Down Converter) IF frequencies explained
9.1 IF Frequencies
• MSR receivers (and many other digital receivers) are capable of receiving direct
frequencies in the range of approximately 49MHz to 861MHz. If the transmitter is
not in this range then a down-converter (also refer to a BDC, block down
converter) is used to convert the frequency to this range. The frequency out of
the down-converter is called the IF (intermediate frequency) which is fed to the
receiver.
not in this range then a down-converter (also refer to a BDC, block down
converter) is used to convert the frequency to this range. The frequency out of
the down-converter is called the IF (intermediate frequency) which is fed to the
receiver.
Down-converters have a LO (local oscillator) which is mixed with the transmitter
frequency (M2T) and converts it to the IF frequency. MSR receivers need to
know the LO (local oscillator) of the down-converter and the RF frequency of the
transmitter. It then automatically calculates the IF frequency. The IF frequency
changes as the RF frequency changes however the LO remains constant.
frequency (M2T) and converts it to the IF frequency. MSR receivers need to
know the LO (local oscillator) of the down-converter and the RF frequency of the
transmitter. It then automatically calculates the IF frequency. The IF frequency
changes as the RF frequency changes however the LO remains constant.
On non-GMS receivers it may be necessary to program the receiver with the IF
frequency directly. The user may have to do the simple math to arrive at the IF
frequency so that it can be entered into the receiver. The down-converter LO
must be known. The math involve is as follows: “LO – transmitter frequency (or
transmitter frequency – LO) = IF frequency”. For example, it the transmitter is set
for 2000MHz and the LO of the down-converter is 2800MHz then the IF frequency
is 800MHz (2800-2000 = 800). The receiver will need to be set to 800MHz to
receive the transmitter frequency of 2000MHz. Each time the transmitter frequency
is changed the IF must be re-calculated and entered into the receiver. It must also
be mentioned, as you may have noticed with the equation “LO-transmitter
frequency or transmitter frequency – LO” that two answers are possible. For
example 2800-2000 = 800 or 2000-2800 = -800. The negative answer may
indicate the receiver wants the signal to be inverted. See section 6.3.3.2 for
inverting the signal.
frequency directly. The user may have to do the simple math to arrive at the IF
frequency so that it can be entered into the receiver. The down-converter LO
must be known. The math involve is as follows: “LO – transmitter frequency (or
transmitter frequency – LO) = IF frequency”. For example, it the transmitter is set
for 2000MHz and the LO of the down-converter is 2800MHz then the IF frequency
is 800MHz (2800-2000 = 800). The receiver will need to be set to 800MHz to
receive the transmitter frequency of 2000MHz. Each time the transmitter frequency
is changed the IF must be re-calculated and entered into the receiver. It must also
be mentioned, as you may have noticed with the equation “LO-transmitter
frequency or transmitter frequency – LO” that two answers are possible. For
example 2800-2000 = 800 or 2000-2800 = -800. The negative answer may
indicate the receiver wants the signal to be inverted. See section 6.3.3.2 for
inverting the signal.
9.2 Local and Remote Power for Down Converters
Customers have the option of using remote or local power:
•
Remote power is provided from the MSR through the BNC connector from each of
the tuners located on the rear panel. Power is turned on through the software control
application (refer to the MSR online manual). The +12Vdc provided from the
receiver will travel through the coax cable to the D/C.
the tuners located on the rear panel. Power is turned on through the software control
application (refer to the MSR online manual). The +12Vdc provided from the
receiver will travel through the coax cable to the D/C.
If the D/C is located relatively close to the receiver then using remote power makes
sense. However, if the D/C is located at great distances away from the receiver
there may be excessive DC voltage drop in the coax cable (due to cable
resistances). If this is the case then local DC power should be considered as
discussed below. If unsure of the DC voltage drop measure the DC voltage present
sense. However, if the D/C is located at great distances away from the receiver
there may be excessive DC voltage drop in the coax cable (due to cable
resistances). If this is the case then local DC power should be considered as
discussed below. If unsure of the DC voltage drop measure the DC voltage present