| To answer the question, you need to divide the amplifiers up by
types and usage, then look at available amplifier technology for output level
capabilities. Since this discussion is primarily about INDOOR
amplifiers, I am not going to include outdoor trunk line modules or upgrade kits. |
| The use of ONE-WAY amplifiers for
distribution amplifier applications is dwindling, but they are the amplifier of choice for
use in headends and hub sites. These amplifiers are usually of a rack-mount design
and break into two basic groups: FORWARD path and REVERSE path amplifiers. Let's
talk about the rack-mount amplifiers first! |
| Forward amplifiers break down into two
sub-groups, which are high-output driver amplifiers, and low-gain isolation amplifiers. The QRAM family of
amplifiers fill the high-output domain with cascaded gallium
arsenide (CGP) power-doubled
hybrids for 750 and 870 MHz models. The high-level duties in this family of
amplifiers is still served by FEEDFORWARD hybrids for 550 MHz and below. There are power-doubled and quadra-power
versions to provide the "not so high-output" range of signal levels from the
QRAM chassis. ALL QRAM amplifiers can be powered from AC and
DC power sources simultaneously. |
| Isolation amplifiers have less gain
since they usually have only a single RF hybrid. The QRBA was created as a general
purpose, high-density amplifier for isolation of entire channel line-ups for franchise
areas, or for narrow-casting VOD and cable modems at the node level. The QRBA forward amplifier chassis can contain up to FIVE push-pull amplifiers or THREE or FOUR power-doubled amplifiers,
depending on powering mode from AC/DC or DC only (four PD models). ALL
forward QRBA amplifiers include a directional coupler for combining the franchise-specific
or narrowcast signals AFTER the RF hybrid. This
configuration can easily provide 60 dB of reverse isolation of the inserted signals to
prevent them from creating interference with other nodes or franchise areas served from a
master headend. Only the broadcast channels pass through the
RF hybrid of the QRBA as part of the distributed headend gain to overcome combining
losses both BEFORE and AFTER this isolation amplifier that
drives fiber transmitters. ALL QRBA amplifiers can be powered
from AC and DC power sources simultaneously. |
| There is one very unusual amplifier in our
forward line of amplifiers: QISO. It was the very first isolation amplifier,
custom built for the cable system serving Pompano Beach and surrounding communities of
Broward County Florida. It was originally intended for use as a SINGLE-CHANNEL, high-output amplifier, but later found use as a
low-level amplifier for broadband applications. As a
single-channel amplifier the RF output is operated in the +57 dBmV range, while the output
for multiple channels is rated at +30 dBmV. This amplifier is designed as a
two-stage, active splitter with 50 dB port-to-port output isolation, operating at unity
gain. The standard model comes with an input directional coupler which allows
multiple units to be "looped together" passively to provide more that the FOUR
outputs available from a single amplifier. The original design
was powered from +24 volts DC ONLY. A newer version allow 26 VAC powering or
+28 VDC powering, but not both at the same time. The same block diagram of this
amplifier is replicated in the QISO/R discussed below for
return path applications. |
| The newest FORWARD amplifier from QRF is a redundant amplifier and switch
in a single rack-unit chassis. The QRED is known as the
"BAQ-UP", which is a name that we trademarked! This is probably the
only place in the web site where that name does not have the TM
superscript with it. This new unit has the first removable
amplifier module we have ever offered. It can have the high performance of
the QRAM but without all the options. It is the first 750/870 MHz amplifier we have
built using a new-style mechanical gain pot for the bridged-T slope and gain controls.
The switch side of this box is passive with the RF filter/amplifier boards and
digital processor board as replaceable boards. The normally closed RF path is always
present even if power fails to the unit. The QRED monitors BOTH the primary existing
headend amplifier and the built-in BAQ-UPTM amplifier all the
time. Any amplifier with an output from +20 to +50 dBmV can be monitored. The
contact closures on the rear panel interface to popular status monitoring systems to alert
you to a failure mode. The dual-input powering of the QRED is
similar to the well-proven QRAM and QRBA line of amplifiers, allowing simultaneous AC and
DC power sources to be used for maximum reliability! |
| Reverse path amplifiers are divided
into two types: push-pull hybrid and single-ended monolithic. The QRBA200 "8-pack" is the most popular for mixed signal
types, while the low-cost high-density QISO/R offers an
active splitter function with 50 dB port-to-port isolation for digital signals with UNITY
gain (0 dB) at +30 dBmV input and output levels. |
| The QRBA "8-pack" uses
low-current push-pull hybrids commonly used in line extenders. Two of these hybrids
are mounted in separate RF cavities to a single heat sink on the back of the chassis.
Each amplifier cavity provides maximum RF isolation from the other amplifiers
inside the chassis. These are simple "one-input, one-output" amplifiers
with a pad and EQ at the input and an output pad as well. The popular
"8-pack" amplifier uses 25 dB gain hybrids and can easily operate at +40 dBmV
output across the range from 5 MHz to 200 MHz. It is designed
to work with external pads and splitters which provide the isolation between receiving
devices in the headend. |
| The QISO/R75-32 provides gain for
digital signals only in the range from 5 MHz to 75 MHz. This
model was also first built for the folks at Pompano Beach. It
is also a unity gain, four-output isolation amplifier, containing EIGHT identical
amplifiers. The loop-through input of each amplifier allows them to be
coupled together to provide up to 32 output ports. Since the bandwidth goes up to 75
MHz, it can be used to amplify digital signals for the forward path above 50 MHz, but is
most commonly used in reverse path distribution in the headend or hub site. It has
the same powering schemes as the forward QISO model, AC or DC, but not both at the same
time. |
| As for the QRF family of wall-mounted
amplifiers, we have a full range of models there as well. Click HERE to learn about those types. |