For the summary
page click here pre
amp_summary
The following is
a comparison of HF
low noise receiving
preamplifiers. More
amplifiers will be
added as they become
available to test.
All instruments used
for these
measurements are
currently calibrated
newer-production
laboratory grade
instruments.
Detailed graphs
will only be added
if specifically
required. The .jpg
pictures on this
page are
examples of how
measurements are
displayed on the
instruments used in
tests.
Gain Compression
Tests
Pre-amplifier
gain compression is
measured on an HP
(Agilent) Vector
Network Analyzer and
S-parameter test set
using the power
level sweep function
at 2 MHz. A gain
compression test
shows loss of gain
as input power is
increased, or the
input level where
the amplifier starts
to saturate.
This test
indicates how much
overall signal power
the amplifier will
handle before gain
is reduced by
non-linearity or
saturation. This is
power or gain
non-linearity, and
really does not
directly represent
distortion level vs.
input or output
signal power. A
correction is
applied to results
for amplifier gain
and equipment
protection
attenuators.
Note: Third-order
intercept is a
better demonstration
of signal level
capacity.
Third-order
intercept better
indicates immunity
of an amplifier to
producing unwanted
signals (mixing
products) from
multiple strong
signals.
ARR 1-30
Amplifier input
power (horizontal
sweep) is 3dB per
division. Measured
1dB compression is
corrected to 21.5dBm
output power @1dB
compression.
ARR GAsFET
(1.8-2 MHz model)
1dB
compression is
corrected to 8.1dBm
output power.
DX Engineering
Push-pull HF
preamplifier
Gain compression
beyond power output
limit of analyzer.
In other words, my
test equipment does
not have enough
output power to
drive the RPA-1
preamplifier into
compression. Actual
corrected gain
compression (manual
test) is
approximately +26dBm
(400-milliwatts
output).
Comparison of
Third Order
Intercept
Third-order
intercept tells us
the immunity of the
amplifier to
generating spurious
signals in the
presence of multiple
strong signals. This
test was at 1.85MHz
using the automatic
IM3 test
measurement. A
stepped attenuator
pad at the amplifier
output was initially
used to prevent
analyzer damage
during testing.
Because of this
“protection”
attenuator, actual
TOI must be
increased by adding
the attenuator value
to the analyzer
display reading.
Third-order IM3
levels occur at the
following single
tone (of an equal
two-tone test):
DXE (early
model) -0dBm input
power (instrument
TOI 17.98+20.2dB
pad= 38.18dB TOI)
Note: Later model
RPA-1 measured 43dB
third order
intercept
ARR
P1-30
-5dBm input power
(instrument TOI
15.38dB+15dB pad=
30.38dB TOI)
ARR GAsFET -16dBm
input power
(instrument TOI
6.09dB+5.3dB pad=
11.39dB TOI)
If you look at
the above
measurements, you
will see third-order
intercept in the DX
Engineering
amplifier occurs
almost 8dB higher
than in the better
performing of the
two ARR amplifiers
that were tested.
Not only is the DXE
3rd order intercept
higher, higher order
products are
substantially less
than the other two
amplifiers produced.
DXE-RPA-1 Test
This is a later
model DXE
preamplifier model
RPA-1. This
measurement has no
external attenuator,
TOI in this case is
a direct reading.
Preamp Noise
Figure
I don’t
have this data saved
to a file yet, but
the noise figure of
the GAsFET amplifier
and the DXE
amplifier are about
the same. The ARR
1-30 had the highest
noise figure, about
5.5dB. All of these
amplifiers are
acceptable for HF
receiving in most
applications so far
as noise figure is
concerned.
Input Impedance
and Gain
So far, the DXE
pre-amplifier has
the closest match to
50-ohms over the
range of 300kHz to
30 MHz. Gain is also
reasonably flat in
the DXE amplifier.
DX Engineering
Preamp
The display above
shows input SWR of
the amplifier on the
top graph, and gain
on the lower graph.
The marker is at
1.834290 MHz. The
vertical graph lines
are frequency at
about 6 MHz per
division. Gain at
marker frequency is
indicated as
16.819dB, SWR is
1.2028:1.
It is also
possible to display
input impedance on a
Smith Chart:
This is the gain
and input impedance
at 1.207440
MHz.
ARR GAsFET
PreAmplifier
This amplifier is
intended to be a
160-meter only
amplifier. It has
high gain despite of
the very poor match
on any frequency. It
also has substantial
gain on all
frequencies swept,
but a strong peak on
1.8 MHz.
Input SWR is
23:1, gain is
26.4dB.
Unfortunately noise
figure is not that
good for a GAsFET,
probably because of
the very large input
mismatch.
The above data is
a Smith Chart
display of the ARR
GAsFET at 1.22 MHz.
Gain is still 13dB,
input impedance is 5
ohms and very
reactive (this
measurement is in
the BCB). Despite
being a
“160-only”
amplifier this amp
has substantial gain
(~15dB) at
60MHz.
Other Data
If you have a
commercial amplifier
or commonly
available
homebrew amplifier
design you would
like tested, please
contact me. I’d be
happy to measure
your amplifier (time
permitting) and post
the results here.
See (soon to be
added) summary
page for text
comparisons.
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