RM HLA-150 test

RM HLA-150 test

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Some people claim
an HLA-150 is a very
clean amplifier. One
odd thing is the
transistors are
specified for about
70 watts maximum
output per
transistor, yet RM
Italy calls the
HLA-150 a “300 watt
PEP” amplifier.
I was very fortunate
in that a nice
fellow loaned me his
HLA-150 for testing.
While I am very
grateful, I will not
mention his name or
call publicly. If
anyone has a similar
popular amplifier
I’d be happy to test
it as time permits.

I found the
saturated power,
into absolute
limits, as 155 watts
PEP with a 13.8 volt
50-ampere power
supply. Gain
compression began at
about 125 watts PEP.

I tested the
amplifier using a
well-regulated 50
ampere 13.8 volt
power supply. I used
two variable power
generators through 6
dB high power
attenuators into a
50 ohm combiner. The
output of the
combiner went into a
3 dB pad into the
amplifier. This is
necessary to ensure
the generators see
50 ohms, and have
good isolation
between each other.

To verify the
generators are
working correctly I
added another 3 dB
pad, and when
adjusted to the same
amplifier power
level IMD
measurements did not
change more than
normal variations
with time.

Power was
measured on a Bird
digital power meter.
It was last
calibrated two years
ago with a 1%

Here are the
actual IM tests.

Generator IMD for IMD test


The test
generator is two 0
to 100 watt signal
sources into a

IMD was into
composite noise.

It is important
to have a very clean
exciter to not
affect the actual
distortion. In this
case the generator
is very clean. The
main problem is
composite noise.






HLA-150 IMD at 55 watts PEP



IMD at 55 watts
output. The extended
or higher-order IM products are of
particular note.
They go on forever
it seems.











This amplifier,
like most, has a
“sweet spot”. The
sweet spot is above
30-40 watts and
below 110-120 watts.


HLA-150 IM tests







90W PEP IM3 is
-29.94 dB one tone
of two equal tones.
This is the method
used commercially
for years by Eimac
and others.

Add -6 dB to get
ARRL type
measurements, which
started to be
popular when the
Collins KWM-380 came
out. This method
makes things look a
little better by
making numbers 6 dB

The RM Italy distortion
is close to that of
nearly all HF
transceivers, except
for  troubling
higher order
products. Products
shown are 3rd, 5th, 7th,
9th, 11th, and 13th.
They actually go on
forever, it seems.

The 13th order
product is only 17
db down from the 3rd
order product.






150W PEP.

3rd order very
poor -14 dB one tine
of two equal tones (-20

While shamelessly
marketed as a 300-watt PEP amplifier, this
clearly is not even a 150-watt PEP amplifier.
At 150 watts PEP
intermodulation is terrible,
much like a class C
amplifier. This is
to be expected
because the
amplifier shows
gain compression
starting at 125
watts PEP. This
makes sense, because
the transistor
the same thing.










distortion at 115 watts PEP is
acceptable, it is
about the same as
any typical radio. 
The high-order
products are not










Summary of IMD
and Power Tests

300 watts PEP: It
is not a 300-watt
PEP amplifier, not
even close. That is
an absolute lie.

150 watts PEP: It
is not a 150-watt
PEP SSB amplifier.
The IMD is far too
high at 150 watts.

120 watts PEP: 
It looks better at
this power. Except for the
wide bandwidth
high-order IM
products, the
HLA-150 is
comparable to most
HF radios in
distortion at a
power output of
115-120 watts PEP.
The high-order IMD
is significantly
worse than the worse
case IM for a
typical 100-watt
transceiver when the
HLA-150 is at 120
watts PEP. 
Above 120 watts
things fall apart
very fast.

watts PEP:

The HLA-150 is
a 90-watt PEP amplifier
at best, and if
operated that way
will be acceptable for many uses. It
not as good as it
could be for the
very wide bandwidth
distortion at higher
power, but it is
comparable to
worse-case IMD for a
common radio like
the FT1000MP when it
is at 90-watts PEP

I was in a bit of
an debate with
someone who insisted
he could evaluate
this amplifier on
PSK31 and other
modes. ( I of course
disagreed with his
test method.) There
are several problems
associated with
using an IMD meter
provided in digi-mode
software. If we look
at the tests above
we see why a PSK
system might
acceptable results
at 50-100 watts. This is
because PSK and
other digital modes
are not concerned
with high-order IMD
products so long as
they are less than
the low-order
products. The higher
order products will
often fall outside the
receiver filter
bandwidth, and not
be registered on the
High-order products
are, for all
purposes, ignored by
the system.
Performance was also tested right in the
“sweet spot” of the


The HL150
amplifier has
exceptionally good
harmonic suppression
on most bands. The
low-pass filters
work well. It is an
acceptable amplifier
when operated at 90
watts PEP output or


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