|VHF/UHF Distribution Preamplifier
3 INPUTS and 8 OUTPUTS
|The finished panel before attaching to the chassis. This assembly is to check for fit and clearance.
During the assembly process...a few
views of the details.
The 500 uA meter with custom face to
accommodate -50dB to +30dB with a "zero"
reference point for 50 uV in a 62 Ohm line.
Why 62 Ohms? The input circuit will match a 30%
impedance swing + or - of 62, or about 40 Ohms to
85 Ohms, Actually, a full 50% swing will introduce
only a small loss due to mismatch. or about 32
Ohms to 93 Ohms.
The chassis in the beginning stages of
The calibration matrix for the various
attenuation levels; 10, 20, 30 and 40
Dual relays to isolate the input and
output RF switching of the active
The antenna selector for three inputs
and a toggle switch wired to allow the
operation mode or shunt mode...for
standby protection...all inputs are
shunted to ground.
The passive attenuator is 4 separate
"L-Pads" and a "thru" position for
The chassis stuffed with all the
Obviously, a lot of cable
dressing and routing are still
needed to make it all look civil.
The actual coax routing.
Note the relay-controlled
RF switch in the center for
isolating the preamp during
More of the cable routing.
The system being tested
for calibration. The FM
tuner section of the EAS
receiver (green) reads
58 uV. That particular
station (92.1 MHz) would
normally be about 23 uV.
Note that the uV reading
is not linear with the
because the receiver has
active AGC circuits that
change the metrics of the
IF gain. The actual gain
is 30 dBv (close to 30:1
In actual use. The signal
level is an amazing 56 uV.
Detail views of the meter and preamp/attenuator controls.