Page 8
RPA-1 User Manual
Mounting at the antenna
Ordinarily, the preamplifier should be mounted at the operating position, rather than at the
antenna. There are a few exceptions, however, including:
•
Pennants, flags, and K9AY loops in quiet locations.
These antennas have relatively low
sensitivity or gain. When used in quiet locations, they do not provide much background
noise to the system. If the feedline loss is high, performance might improve with the
preamplifier mounted near the antenna.
•
Small loops (magnetic loops).
These antennas also lack sensitivity, and may require
mounting the amplifier near the antenna when cable runs are lossy.
Determining the sensitivity
The following is a simple method to confirm adequate sensitivity. This test generally requires the
assistance of another operator:
1. Listen at the quietest expected operating time with the receiver set to its narrowest
selectivity.
2. Remove all receiving antennas from all feedlines.
3. Replace the antennas with a resistor load of the same impedance as the antennas.
4. When the load is substituted for the antenna, a noticeable decrease in noise should
occur.
It is advantageous to have receiver AGC action begin just above noise floor, while avoiding
excessive levels of background noise. This usually occurs when there is a perceptible
increase in S meter reading, when the antenna is connected. If background noise is high or
your receiver is overloaded, you can add an attenuator pad or remove power from the
RPA-1. Removing power bypasses the RPA-1.
Connecting the power supply
The RPA-1 requires a well-filtered 10-18 Vdc source with a negative ground
.
A wall-wart
or station power may be used, but must have an inline 1 or 2 ampere fast-blow fuse if the
supply is capable of providing more than 1A of current. .Place the fuse at the power supply,
rather than at the RPA-1.
Page 5
RPA-1 User Manual
Third Order
Intercept
Figure 1 below illustrates a
typical production RPA-1
output third order
intercept measurement.
The RPA-1 is significantly
more immune to overload
than the best commercial
amateur receivers. Third
order products are 50 dB
below +18 dBm output.
Figure 1.
A typical third order intercept of the RPA-1.
