Twin Multicoupler Amplifier
Broadband: DC to 1.2 GHz
Having built several HF Multicouplers and VHF/UHF Distribution Amplifiers, I thought it was time to integrate the several bands into one chassis. I've
used MMIC chips, FET preamps and straight bipolar devices to achieve the amplification required to make up for the splitter losses. Lately I've been
evaluating some of the video chips that are available. These seem to be of sufficiently low noise and suitable dynamic range. One such family is the
LM1252, along with some variants that have better specs in various areas. But for now, we will be living with this one for continued beta trials. These
video amps are good to 30 MHz or more, but won't satisfy the need to cover VHF and UHF frequencies.
Again, playing with various devices proved to be educational, but I kept coming back to the products that have already proved themselves in
practical application. One such family are the typical "drop amplifiers" used for CATV systems. Typically these are 15 dB amps and quite quiet for
sensitive upper-band DX.
Here is the layout of the TMA-1. It is modulized for control of the HF (shortwave) band and the upper bands for VHF and UHF coverage. The third
module contains some power line filtering and a mains tester for polarity and electrical ground.
Views of the 3 modules. Note that the HF section has a true
Attenuator for RF Gain. The IC amplifier has an active gain
control (in op-amp fashion). There is also a signal bypass
switch and an antenna shunt switch. Bi-color LEDs indicate the
operational state with red and green colors.
The middle module controls the drop
amplifier. The input of the amp is fed
from an L-pad to control possible
overload. This acts like a true RF
The third module controls AC mains power. It has a polarity confirm indication circuit.
Red = hot, Yellow = return, green = safety ground. If the power lines, anywhere in the
system have become reversed or mis-wired, the indicators will show the fault.
Additionally, there are MOVs, Transorbs and hash filters added. Their state is shown
with the amber LEDs.
Here is the basic layout. All the modules are built
and tested before incorporating them into the
system. This makes for a simple and neat assembly.
This view shows the connector arrangement. There
is a single F-connector input for the VHF/UHF
section with 8 isolated outputs.
The HF side has a single SO239 input with 8 BNC
outputs. The video amp (in the silver case) is
configured for 20 dB gain (variable). The
distribution amp offers significan HF port-to-port
isolation and is good down to the VLF band.
I'll add more as we beta test this unit.