Commercial Cable Television Products
Question:
I have several of the TMQAM modulators running 64 QAM and recently I added a TMQAM/asi modulator, which I want to operate at 256 QAM, but I can't get it to function.
Answer:
When running 256 QAM, it is necessary to change the BD RATE to 5.3606 instead of the 5.057 baud rate or symbol rate used for 64 QAM.
Question:
We have recently added a few digital channels to our system, using the DDC806 digital down converter and the DUC550 and DUC860 up converters. We noticed some interference, when we try to select an output channel on the DUC that is adjacent to an existing analog channel.
Answer:
When an analog NTSC signal is present on the lower adjacent channel to the selected digital input channel of the DDC806, there will be some amount of the audio carrier (250 kHz below the edge of the selected channel) from this lower adjacent NTSC signal present in the IF output of the DDC806. This is then translated to the new output channel with the DUC upconverter, even though it will also be attenuated some in the upconverter. This will not cause a problem if the translated output channel has no channel or another digital channel located in the lower adjacent channel position in the output channel lineup. However, if there is a NTSC analog channel located adjacent to the lower edge of the translated digital channel, there will be a potential beat formed between the audio carriers of this lower adjacent analog and the translated lower adjacent analog. To avoid this potential problem, avoid having a lower adjacent analog at both the input and output of the translated digital channel(s). It is OK if there is a lower adjacent NTSC signal at either the input or output sides - just not both.
Question:
We have several of the DQT861 transcoders and we need the MPEG program number of each off air channel to have our set top boxes programmed. Is this number the same as the digital channel number?
Answer:
The digital channel numbers are not necessarily the same as the MPEG program numbers. The MPEG program numbers are the numbers that are displayed on the DQT861 front panel as it is reading the tables and building the new output tables for the multiplex. Usually this goes by so fast that you can't really see anything.
The DQT861 has a unique feature that will allow you to see the MPEG program numbers as the unit is reading the tables and building the new output tables for the multiplex. The DQT860 also has this feature if the software is version 1.1 or higher.
Since your units have been installed and are up and running, go into the program mode by pressing the ENTER button until display starts to flash. Once the display starts to flash, exit the program mode by pressing and holding the ENTER button depressed. Normally you press the ENTER button momentarily to exit the program mode, to see the MPEG program numbers as you exit the program mode, you must press and hold the ENTER button depressed. While the unit is reading and building the new tables, it will pause for approximately 1 second on each table to allow reading of the program number. Once read, release the ENTER button and the DQT861 should return to normal operation.
NOTE: The MPEG number read for Demod B will NOT include the mux offset amount you entered during set-up, you must add the mux offset number to this reading.
NOTE: If you are NOT using the DQT861 in multiplex mode, with the optional 2nd Demod kit or factory installed dual demodulators, the above will NOT apply as no tables are being generated and nothing will be displayed.
Question:
I noticed that several of your rack mount models have small exhaust fans. Does this mean that I can stack the units without a space?
Answer:
The exhaust fan is to provide air movement through the unit. When the unit is mounted above or below other rack mounted equipment, a 1U space should be left between the unit and the other equipment to allow ambient air flow between the units.
Question:
I just received the DQT861 Digital QAM transcoder and I am feeding in two off air encrypted signals. I get a FIFO OVERFLOW message, what gives?
Answer:
When you select the QAM mode, you will see several selections including QAM-256A and QAM-256B The A suffix indicates ITU-A or DVB compliant FEC and the B suffix indicates ITU-B or DigiCipher II FEC encoding. Selecting QAM256A with DigiCipher signals will result in the above error message. If you have selected 256B and still have the FIFO OVERFLOW message, the input data rate could be in excess of 19.4 Mbps. In this event, the DQT861 will allow you select which Mpeg programs are passed and which are filtered out to reduce the data rate. Please refer to the instruction manual for details on SELECT PROGRAMS.
Question:
I have two off air channels going to the DQT861 and it appears to be working, but I can't find the second channel.
Answer:
When you set up the DQT861 for the second channel, you were instructed to enter a Mux offset. This is done to avoid conflict with overlapping use of MPEG program numbers. This same offset value is added to the minor channel number and the set top box must be mapped accordingly.
Question:
I have the DQT861 transcoder, can I check the output level with an analog meter or analyzer?
Answer:
Yes, the Drake transcoders, including the DQT861, have a unique feature that will allow you to use the analog meter or analyzer. When switching the DQT861 into the CW mode, the transcoder will output a single unmodulated CW carrier at the center frequency of the output channel.
Question:
We have intermittent operation and some tiling with the DQT861 units. The signal will drop out intermittently.
Answer:
Intermittent loss of signal is usually associated with inadequate signal getting to the transcoder. The front panel SNR reading must be above the 15 dB threshold level for an 8VSB signal, above 23 dB for 64 QAM, and above 27 dB for 256 QAM. Typical SNR readings are above 25.
Question:
I have misplaced the instruction manual for the HCP2550 channel processor and I can't remember the dip switch settings.
Answer:
You can download the dip switch settings from our web site.
Question:
I have the HCP2550T channel processor, which was working fine until I switched to a T-channel. I have checked all switch settings, I have the composite loop in place and nothing works.
Answer:
When using the HCP2550T or the HCP1550T unit on a T-channel. The signal must be fed into the "T-channel input" and a jumper must be added between the "Up-converter output" and the "RF input".
Question:
I have several of the DA8642 distribution amplifiers and I have one unit that has failed. It will not come on, yet I can measure output from the AC power adapter.
Answer:
All Drake distribution amplifiers have an internal fuse. The internal fuse is a 2.0 amp and is mounted in a fuse holder for easy replacement.
Question:
I am adding a security camera to an installation by using the VM286, however I can't get a signal from the VM286.
Answer:
The VM286, as well as the VM2551, has an IF input and an IF output on the rear apron for use with an external scrambler or an alternate video source. A short coax cable is supplied with the VM286 to connect these two ports, make sure this cable has been installed.
Question:
I have ordered a VMM860AG video modulator and a MMTS20 stereo encoder, I have a few VMM600 modulators with the MMTS20 stereo encoders and I remember having to defeat the audio pre-emphasis by moving an internal jumper, as outlined in the instruction manual. Do I need to do this in the VMM860AG as well?
Answer:
No need to open up the VMM860AG, the VMM860AG has a switch on the rear panel that will allow you to select "FLAT" pre-emphasis.
Question:
I just received a VMM860AG unit and I can't measure an output.
Answer:
Be sure to set the front panel "mode" switch. This switch must be set in the BCTV for Broadcast TV, CATV for cable TV channels 02 to 99, or CATV+100 for CATV channels 100 to 135.
Question:
I have the VMD806AG or VMR806AG and it has no output.
Answer:
Be sure to set the front panel "mode" switch. This switch must be set in the BCTV for Broadcast TV, CATV for cable TV channels 02 to 99, or CATV+100 for CATV channels 100 to 125. In addition, the T-channel switch must be set properly.
Question:
I have been using the DUC860's with great success. I switched one unit down to channel 75 and all I get is a flashing power/error light and no output.
Answer:
The DUC860 will not operate below CATV channel 78 and broadcast channel 27. The DUC550 will be required for the lower channels below 550 MHz. The DUC864 covers the entire 54 MHz to 864 MHz output range.
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