DX Engineering RPA-2 User manual

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RPA-2 HF Modular Receive
Preamplifier
DXE-RPA-2
DXE-RPA-2-INS Rev 2a
U.S. Patent No. 7,319,435
© DX Engineering 2019
1200 Southeast Ave. - Tallmadge, OH 44278 USA
Phone: [phone] ∙ Tech Support and International: [phone]
Fax: [phone] ∙ E-mail: [email protected]

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Introduction
The DX Engineering DXE-RPA-2 Modular Receive Preamplifier is a high-performance broadband
LF through HF receiver preamplifier that features exceptional immunity to overload. It also has an
excellent noise figure and a low input SWR, optimized
for the 300 kHz to 35 MHz range. Meticulous
craftsmanship and durable, robust components allow this
50-ohm preamplifier to withstand high signal levels
while providing superior dynamic range and third-order
intercept performance that equals or exceeds most
receiver and transceiver front-ends. Unlike other external
preamplifiers and many transceiver internal
preamplifiers, the RPA-2 enhances the readability of
weak signals without artificially increasing the noise. On low bands and beyond, weak signals
become more intelligible using this preamplifier in conjunction with proper adjustment of the RF
Gain and Attenuator in the transceiver.
The RPA-2 is a combination of a redesigned aluminum shielded enclosure chassis with the DXE-
RPA-2-PM Receive Preamplifier Plug-in Module factory installed. The DXE-RPA-2-PM module
retains the essential characteristics of the milestone product, the original DX Engineering RPA-1.
Featuring one internal optional module slot, the RPA-2 allows the use of the optional DXE-IT-PM
75 to 50-ohm Impedance Transformer Plug-in Module or the optional DXE-RG5000HD-PM
Receiver Guard Plug-in Module or optional filter. See DX Engineering Receive Filters.
While many other common preamplifiers suffer from harmonic distortion, the DXE-RPA-2 low-
noise preamplifier features an advanced push-pull design that eliminates harmonic distortion. High
quiescent current increases its ability to handle strong signals without distortion or overload. This
high performance device must be powered with a well filtered and regulated DC power supply and
offers maximum performance at +13.8 Vdc to +18 Vdc input. Never use an inexpensive, poorly
performing wall transformer to power this top-of-the-line preamplifier.
Features
Internal circuit impedance of 50-ohms for direct connection to 50-ohm receive systems and
antenna feedline BNC connectors with no transformer required
Internal slot accommodates the optional 75 to 50-ohm Impedance Transformer Module to
accomplish transition from a typical F connector 75-ohm receive antenna feedline to 50-ohm
equipment, without losses
Input and output connectors BNC and F types, prevent accidental connection to transmitting
devices
Automatic RF bypass relay also turns the preamp off when the dc power is removed
Green LED indicates when DC power is present and the preamplifier circuit is engaged
An ingenious positive-capture threaded-sleeve 2.1 mm power connector that ensures the DC
power cannot be accidently disconnected from the RPA-2
A simple internal jumper allows the RPA-2 to be powered by DC on the feedline for use on
antenna types that require a preamplifier at the antenna such as Pennants, Flags or K9AY Loops

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Additional Requirements
Please note you will need to consider the following requirements (parts not included in this
package) to install and operate the RPA-2 HF Preamplifier:
The RPA-2 requires a well-filtered, negative ground, +13.8 to +18 Vdc @140 mA power source.
Depending on the supply current, you should use an inline fuse. Alternatively, powering the RPA-2
through the coax feedline requires a voltage injector circuit (not included) and an internal jumper
(HD5) change. See the section “Powering Through the Coaxial Cable”.
Installation outdoors at the antenna is not normally needed or recommended. However, some antenna
types such as Pennants, Flags or K9AY Loops require a preamplifier at theantenna. If you are
mounting the unit outdoors, you will also need to mount the RPA-2 in such a manner as toprevent
moisture entering the unit.
Specifications of the DXE-RPA-2 Receive Preamplifier:
Input and Output Connectors, female: BNC and F
Frequency Range: 300 kHz to 35 MHz
Gain: 16 dB, +/- 1.5 dB (over entire frequency range)
Output Third Order Intercept: 43 dBm
Noise Figure: 3.5 dB
One dB Compression Point: +26 dBm (400 mW output)
Dynamic Range, IM3: 110 dB or greater (500 kHz BW)
Power Requirement: +13.8 to +18 Vdc, 140 mA max.
Operating Temperature Range: -10°F (-23°C) to 150°F (65°C), non-condensing
The following are simplified explanations of information highlighted above.
Third Order Intercept - A
standard measure of how well a
receiving system performs in
the presence of strong nearby
signals. The higher the third
order intercept (TOI), the less
likely adjacent strong signals
will cause interference. The
RPA-2 offers substantially
improved TOI over competitive
preamplifiers and
communication receivers. The
figure to the right illustrates a
typical RPA-2 output third
order intercept measurement.
The RPA-2 is significantly more immune to overload than the best commercial amateur
receivers. Third order products are 50 dB below +18 dBm output.

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Noise Figure - The ratio of equivalent noise power developed at the input to that generated by
thermal noise in the source resistance, usually expressed in decibels. If it were possible, a
perfect amplifier would have a noise figure of 0 dB. The RPA-2 is extremely quiet, and does not
contribute noticeable noise to receiving systems. Almost all HF antenna systems receive an
ambient noise level that is greater than the noise floor of the RPA-2.
Dynamic range - The ratio of the faintest signal detected to the loudest signal amplified without
significant distortion, typically expressed in decibels. The RPA-2 allows you to hear faint
signals in the presence of adjacent strong signals.
Gain - The ratio of signal input to output. The RPA-2 features a modest gain that may be
bypassed when not needed by removing power to the unit.
ATTENTION: Never transmit through the RPA-2.
The unit can be damaged by direct application of transmitter power.
Installation Location Considerations
Optimum electrical location of the RPA-2 varies with antenna system background noise level. A
good receiving system requires the antenna to establish system noise, not the preamplifier. A
common myth is that a preamplifier must be mounted at or near antennas to be effective. This is not
true at low VHF, HF and lower frequencies. A preamplifier is needed at the antenna only when
feedline loss is high and the antenna has very low background noise. Low band antennas rarely
suffer from feedline losses, so the preamplifier can normally be used at the radio. Another common
misconception is that mounting the preamplifier at the antenna feedpoint reduces feedline noise
pickup. The location of the preamplifier rarely makes a difference in feedline noise. Most feedline
noise couples back to the antenna at the antenna terminals, it does not leak directly into the feedline.
The RPA-2 prevents signal leakage when used at an antenna.
Normal Mounting Indoors
For typical indoor installations, mount the RPA-2 near the receive antenna input of receiver or
transceiver. For best results, use the RPA-2 in a well-ventilated indoor area away from direct
sunlight and moisture. Operation outside of the specified temperature range of -10°F (-23°C) to
150°F (65°C), non-condensing, will shorten the life of the RPA-2, and should be avoided.
Mounting at the Antenna
Ordinarily, the preamplifier should be mounted indoors at the operating position, rather than at the
antenna. There are few exceptions which include Pennants, Flags, and K9AY Loops. These
antennas have relatively low sensitivity and will not provide much background noise to the
system when they are installed in quiet locations. If the feedline loss is high, performance
might improve with the preamplifier mounted near the antenna.
The RPA-2 may be mounted at or near the receive antenna under a cover or in a weather-protected
enclosure. Operation outside of the specified temperature range of -10°F (-23°C) to 150°F (65°C),
non-condensing, will shorten the life of the RPA-2, and should be avoided. Make certain that the
enclosure is vented to prevent moisture from collecting in the unit that would accelerate corrosion

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and failures. A remote power source of +13.8 Vdc minimum may be used. Alternatively, the RPA-
2 may be powered over the coax. See “Powering Through the Coaxial Cable”.
Power Connection
The RPA-2 requires a well-filtered +13.8 to +18 Vdc @ 140 mA source with a negative ground.
Many inexpensive wall mounted transformer DC supplies are not 'clean' and have RF noise
components on their DC output. Place the fuse at the power supply, rather than at the RPA-2.
The RPA-2 power connector uses a positive locking threaded 2.1 mm barrel
type plug (included). When plugged in, tighten the connector by turning
clockwise. This prevents the power connector from coming loose. To
remove, turn the connector counterclockwise. You should use a well
regulated +13.8 Vdc supply. Another well regulated source can be used as
long as it supplies +13.8 to +18 Vdc, negative ground, the power plug center is connected to
positive and has an inline 1A fuse. When power is applied to the RPA-2, the green LED will
illuminate. A standard 2.1 mm power connector with center positive and +13.8 Vdc supply may be
used. Do NOT use a wall transformer, they are inherently noisy.
ATTENTION! Be sure the power supply polarity and voltage level are correct.
Opening the RPA-2 unit
To open the RPA-2 unit, remove the six Phillips head screws and
the case will come off exposing the interior printed circuit boards.
The top slot has a By-Pass Module installed and the bottom slot
has the RPA Printed Circuit Board installed.
View looking from the rear of
the RPA-2 with the cover removed.
Powering Through the Coaxial Cable
The RPA-2 has a three-pin internal jumper header
labeled HD5. The factory default (as shown) has
the jumper installed onto the lower two pins of
HD5.
With HD5 in the factory default position, the DC
power connected from the units 2.1 mm connector
labeled “POWER 12 Vdc” feeds the internal
RPA-2-PM Receive Preamplifier Plug-In Module
and another optional board, as needed.

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Alternatively, if the RPA-2 is to be located at the receive
antenna, the unit may be powered from DC on the feedline
that is connected to the “RECEIVER OUTPUT”
connectors. This requires a user supplied bias-tee or
feedline voltage inserter used at the operating position,
providing the properly filtered and regulated (center-
positive) +13.8 Vdc, 140 mA minimum.
To enable powering the RPA-2 via the coaxial cable,
move the HD5 jumper to the top two pins.
RPA-2 Powered by RPA-2 Power
2.1 mm Connector from Coax
(default) Cable
NOTE: The ability of the RPA-2 to be powered on
the “RECEIVE OUTPUT” coaxial cable cannot be extended to the antenna feedline. In other
words, when the RPA-2 is powered on the coax, any active devices used on the “ANTENNA
INPUT” side of the preamplifier will require separate power connections.
Information on Gain for the RPA-2
The DXE-RPA-2 Preamplifier and the DXE-RPA-2-PM Preamplifier Plug-in Module do not have a
gain adjustment control. All specifications are optimized for 16 - 17 dB gain as set by the circuit
components. If signals are overloading your receiver or if background noise is excessively high,
here are two gain reduction solutions.
The first and simplest gain reduction solution is to use an attenuator. The simultaneous use of the
pre-amplification of DXE-RPA-2 and the step attenuator in the transceiver or receiver, along with
fine adjustment of the RF Gain control, is an extremely effective technique for improving
intelligibility of weak signals. Using the step attenuator built into your radio is essentially the same
as using an inline attenuator pad on the RPA-2 output. This increases the receiver’s overload
threshold, while preserving the preamplifier’s specified performance, including input intercept* and
noise figure, which remain essentially unchanged. Conversely, adding a conventional inline
attenuator on the input of the RPA-2 will reduce its noise figure roughly by the amount of the
attenuation. This is usually not a problem with modest antenna efficiency. With a decrease in noise
figure the input intercept and overload limit increase. As a general rule, reduction of gain with an
attenuator pad at either the input or output of this preamp will not compromise system performance.
This is because the RPA-2 design has a very large performance margin in both noise figure and
intercept.
The second gain reduction solution, if desired, is a "permanent" reduction of gain level by
modification of RPA-2 surface mount devices (SMD) in the FET push-pull circuit.
Please Note: The following is an advanced modification that should be performed by electronics
technicians familiar with SMD PC board soldering techniques.
Reduction of the RPA-2 gain by about 3 dB is accomplished by removing two capacitors, C3 and
C6, from the push-pull circuit. Additional gain reduction of about 4 dB is achieved by soldering one

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1,500 ohm 0.25 watt resistor (SMD 1206 package) in parallel with R1 and another in parallel with
R6. Be aware that gain reduction modifications will cause the performance of the RPA-2 to
diminish above 15 MHz. Modifications, if done incorrectly as described, are not covered by
warranty.
*For more information on receiver and receive preamplifier performance measurements, including
third order intercept, see The ARRL Handbook for Radio Communications.
Installing an Optional Plug-in Module
The RPA-2 has an internal open slot that will accommodate
either the optional DXE-RG5000HD-PM Receiver Guard or
the optional DXE-IT-PM 75 to 50-ohm Impedance
Transformer. Current RPA-2 model has a black case.
The Bypass Module will have to be removed to allow
installation of the chosen optional board.
With the RPA-2 opened, use a round screwdriver to gently pry the bypass module as shown below.
Do one side at a time and the module will come out. When installing the chosen optional module,
align the pins and press both ends of the module equally until the chosen option module is fully
seated.
Lightning
While most amateur radio installations rarely suffer damage from lightning (even though they never
disconnect their equipment); the best protection is to disconnect electrical devices during storms.
The key to proper lightning survival is proper grounding of feedlines and equipment, and
maintaining integrity of shield connections. A proper installation improves lightning protection and
enhances weak-signal receiving performance. The DXE-RLP-75FF Lightning Protector, 75-ohm,
DC Pass, Type F Connectors is one optional device that could be used. Consult lightning protection
and station grounding information in the ARRL handbooks, the National Association of
Broadcasters (NAB) handbook or other reliable sources.

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Optional Plug-in Module Descriptions and Specifications
75 to 50-ohm Impedance Transformer Plug-in Module (DXE-IT-PM)
A perfect match for changing the line impedance between 50 and 75-ohm systems
Frequency Range: 500 kHz through 30 MHz
Insertion Loss: <0.1 dB at 15 MHz, <0.2 dB at 30 MHz
Power Handling: over 30 dBm
Impedance: input = 75-ohms unbalanced
output = 50-ohms unbalanced
Receiver Guard Plug-In Module (DXE-RG5000HD-PM)
This highly effective and inexpensive receive RF limiter prevents front-end damage due to high RF
levels that can result in costly radio repairs.
Frequency Range: 0.5 through 150 MHz
Insertion Loss: < 0.15 dB at 50 MHz, < 0.3 dB 50 MHz up to 150 MHz
VSWR: < 1.2:1
Max Output Level: +14 dBm at 10 W input.
Maximum Power Handling: 10 W CCS (Continuous Commercial Service)
System Impedance: 50-ohms, unbalanced
Technical Support
If you have questions about this product, or if you experience difficulties during the installation, contact DX
Engineering at [phone]. You can also e-mail us at: [e-mail]
Manual Updates
Every effort is made to supply the latest manual revision with each product. Occasionally a manual will be
updated between the time your DX Engineering product is shipped and when you receive it. Please check the
DX Engineering web site (www.dxengineering.com) for the latest revision manual.
Warranty
All products manufactured by DX Engineering are warranted to be free from defects in material and workmanship for a period of one (1) year from
date of shipment. DX Engineering’s sole obligation under these warranties shall be to issue credit, repair or replace any item or part thereof which is
proved to be other than as warranted; no allowance shall be made for any labor charges of Buyer for replacement of parts, adjustment or repairs, or
any other work, unless such charges are authorized in advance by DX Engineering.
If DX Engineering’s products are claimed to be defective in material or workmanship, DX Engineering shall, upon prompt notice thereof, issue
shipping instructions for return to DX Engineering (transportation-charges prepaid by Buyer). Every such claim for breach of these warranties shall be
deemed to be waived by Buyer unless made in writing. The above warranties shall not extend to any products or parts thereof which have been
subjected to any misuse or neglect, damaged by accident, rendered defective by reason of improper installation, damaged from severe weather
including floods, or abnormal environmental conditions such as prolonged exposure to corrosives or power surges, or by the performance of repairs or
alterations outside of our plant, and shall not apply to any goods or parts thereof furnished by Buyer or acquired from others at Buyer’s specifications.
In addition, DX Engineering’s warranties do not extend to other equipment and parts manufactured by others except to the extent of the original
manufacturer’s warranty to DX Engineering.
The obligations under the foregoing warranties are limited to the precise terms thereof. These warranties provide exclusive remedies, expressly in lieu
of all other remedies including claims for special or consequential damages. SELLER NEITHER MAKES NOR ASSUMES ANY OTHER
WARRANTY WHATSOEVER, WHETHER EXPRESS, STATUTORY, OR IMPLIED, INCLUDING WARRANTIES OF MERCHANTABILITY
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STRICTLY IN ACCORDANCE WITH THE FOREGOING.
©DX Engineering 2019
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Specifications subject to change without notice.