How much equipment is needed to operate an LMDS
television system?
How far will a Master Transmitter
(HPTx) transmit?
Why is your master transmitter
contained in a single cabinet?
Can I install the
equipment with my own engineers and technicians?
Can
I maintain the equipment with my own engineers and technicians?
What
type of RF power amplifier does the Dudley Lab Master Transmitter
use?
What is the expected service life of a
TWTA?
Is the Dudley Lab equipment redundant?
What is a Linearizer?
Why is the Dudley Lab
system 48 channels?
Why do you send the TV signals to
the HPTx with two cables of 80-540 MHz?
Why are 12
modulators in a cage instead of separately packaged?
Do
I need an Antenna/Downconverter unit for every user in an apartment
complex?
How do I get the signal to the Repeater
Transmitter (RTx)?
What are your plans for digital
television and computer data networking?
Do you have any
plans to offer an all solid-state Master Transmitter for television or
data?
Does Dudley Lab offer optional
equipment?
Q. How much equipment is needed to operate an
LMDS television system?
A. You will need the following items in
addition to your standard satellite downlink, cable feed, or studio equipment
that provides the programming as baseband audio/video sources. For your head
end, a Master Transmitter (HPTx) is required, and for each
channel of programming, a modulator is needed as well.
For a typical 48 channel system, you will need 48 modulators plus one Master
Transmitter. You will also need an Antenna/Downconverter and a
Tuner Box for each
subscriber. There is no other equipment required, as all cables and mounting
brackets are included. This start-up system would be capable of providing
service to subscribers 3 to 4 miles from the master transmitter.
The Head
End start up cost for a Master Transmitter with 48 channels of FM modulation is
in the range of US$350,000
Q. How far
will a Master Transmitter
(HPTx) transmit?
A. With the low cost receiver
Antenna/Downconverter unit, approximately 3 miles. This range can be extended
to approximately 4 miles if a medium cost Antenna/Downconverter unit is used.
This range can be extended even further, to about 6 or 7 miles, with a premium
Antenna/Downconverter. To get the most cost efficient system, most customers
choose to use a mix of low, medium and premium cost Antenna/Downconverter
units.
Q. Why is your Master Transmitter
(HPTx) contained in a single cabinet?
A. Dudley Lab's master
transmitter (HPTx) is designed
from scratch for the LMDS/CS industry, and consists of a single cabinet with
air conditioning included, and heating is provided when required. We feel that
this approach results in a product that is more reliable, quicker to install,
and easier to service.
Q. Can I install the
Dudley Lab system with my own engineers and technicians?
A. Yes. All
Dudley Lab systems are designed and built with that in mind. The television
system is a two unit configuration consisting of a rack cabinet of modulators
at the head end, and the master transmitter cabinet on the tower or rooftop.
This configuration is very easy to install. Each system is tested as a complete
system before shipment, and includes all of the mounting brackets, cables, and
documents necessary. We also provide technical training for your engineer
before delivery of the equipment.
Q. Can I
maintain your equipment with my own engineers and technicians?
A.
Yes. The system is modular in design, and each module can be tested and
replaced if necessary in the field. Additionally, we provide at no cost 24 hour
technical support from our web site. This service provides detailed information
related to specifications and test procedures.
Q. What type of RF Power Amplifier does the Dudley Lab
master transmitter use?
A. All of our system master transmitters for
television (HPTx's) use
traveling wave tube amplifiers (TWTA's). TWTA's can provide 60 watts of
operational power when used with a linearizer, while the maximum power from a
solid state amplifier at LMDS frequencies is only a few watts. It is possible
to build a transmitter with solid state amplifiers instead of TWTA's, but it
would require many of them for a television system. Such a transmitter would
also be relatively difficult to build, install, and service. For a digital data
system, solid state amplifiers are much more practical. We are offering this
type of system now.
Q. What is the expected
service life of a travelling wave tube amplifier?
A. The first
high-power transmitters (HPTx's) that we delivered to Venezuela have been in
continuous operation for over 4 years. We believe that this long life is
largely due to the air conditioning system we use for all of our Master
Transmitters.
Q. Is the Dudley Lab
equipment redundant?
A. The issue of redundant components is a
difficult one, since it is difficult to determine which component(s) may fail
in operation. Because the failure of one of many parts will result in an off
the air condition, we recommend that a complete spare Master Transmitter be
installed at the head end. This transmitter may be switched on automatically by
a control computer. The cost of purchasing two complete transmitters from
Dudley Lab is about the same as purchasing one partially redundant unit from
other manufacturers.
Q. What is a
Linearizer?
A. A Traveling Wave Tube Amplifier (TWTA) distorts the
RF signal during the amplification process. This distortion is in both
magnitude and phase. Distortion is normally reduced by operating the TWTA's at
1/4 of their maximum output power. A linearizer pre-distorts the signal in the
opposite direction of the TWTA. As a result, when the RF signal is
pre-distorted by a linearizer and then re-distorted by the TWTA, it is closer
to the desired signal at a higher output power. The normal improvement in power
output is 3 dB or double that available without the linearizer. The end result
for the equipment user is higher power output and lower distortion. Dudley Lab
includes linearizers at no additional cost as part of our master transmitters
(HPTx) and repeater
transmitters (RTx).
Q. Why is the Dudley Lab system 48 channels, when it would
appear that 1000 MHz would support 50 of the 20 MHz channels?
A. Our
2 block conversion system requires 10 MHz on each side of the system center
frequency for the Diplexer/Filters, which accounts for 20 MHz. The other 20 MHz
is used as RF guard band: 10 MHz at the band top and 10 MHz at the band bottom.
This configuration is somewhat technically conservative. However, this spectrum
is not lost forever as we have plans to offer digital services in this region.
For the Korean market, where there is 800 MHz allocated, we provide 40 channels
on a single IF cable.
Q. Why do you send
the TV signals to the HPTx with two cables of 80-540 MHz?
A. This
approximate band is commonly used by other modulator manufacturers, also, this
frequency range allows our customers to run very long cables from their head
end equipment to the Master Transmitter (up to 600 feet). Since we also
manufacture the video modulators, we could have chosen a single block of
frequencies, from say 1500 to 2500 MHz. This would have lowered the cost of the
transmitter slightly, but would have limited the customer's modulator
purchasing options. We do offer a single block feed on special order that uses
coaxial cable for up to 200 feet or fiber-optic cable up to 2 kilometers.
Q. Why are there 12
modulators in a cabinet
rather than separately packaged?
A. We believe that the overall cost
of an LMDS/CS system is very important, and we are able to reduce costs by
sharing the power supply and frequency converter between 12
modulators.
Q. When providing television
service to an apartment building, do I need to have an Antenna/Downconverter
unit for every apartment?
A. No, we have an
8-way splitter that may be
used to provide service to 8 apartments from a single
Antenna/Downconverter. This
8-way splitter unit has an amplifier that compensates for the losses of the
splitter plus 100 feet of additional cable. This method is also very
economical, since sharing one Antenna/Downconverter will allow you to purchase
a higher quality unit, allowing greater range from the transmitter.
| Case 1 | Single user with low-cost antenna and tuner box | $170 + $140 = $310 each | Cost Per Subscriber: $310 |
| Case 2 | 8 users with low-cost antenna, 8 tuner boxes, and one splitter | $170 + $1,120 + $71 = $1,361 | Cost Per Subscriber: $170 |
| Case 3 | 8 users with premium antenna, 8 tuner boxes, and one splitter | $300 + $1,120 + $71 = $1,491 | Cost Per Subscriber: $186 |
Q. How do I get the signal to the
Repeater Transmitter
(RTx)?
A. Normally, we use a
Point-to-Point Link (LNK-1).
The link can relay the programming about 6 miles to our High Power Repeater
Transmitter (RTx). Another method would be to use fiber-optic cable in place of
the link. This is a good approach where fiber-optic cable is
available.
Q. What are your plans for
digital television and computer
data networking?
A. Digital TV will depend on the market. It is
currently very expensive for the system operator to provide digital
tuner/decoder boxes to the subscribers. Industry studies indicate this high
cost is likely to continue for some time. Computer services are another matter
because the subscribers are likely to be willing to pay the required rates to
support the system and the cost of providing computer services is actually less
than the cost of providing digital TV. We have a CATV type modem
LMDS system available
now.
Q. Do you have any plans to offer an all
solid state Master Transmitter for television or data?
A. Not for
television at this time. We began a design in 1996 and found that the cost
savings were small, if any, and the complexity of the system was much higher.
We are offering a solid state, 90 degree,
sector transmitter system
for data applications. The range is approximately 3 miles, somewhat less than
with an HPTx, and is for Internet and data services only.
Q. Does Dudley Lab offer optional
equipment?
A. The products shown on our web site are those that are
ready for full commercial systems deployment. For experimental or evaluation
purposes, we can provide a wide range of options. Please call for
details.
If you have any other questions, contact me by email and I will try
to answer them here.
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