FLEX-5000 Accessories and Upgrades


FLEX-5000 RX2

The FLEX-5000 Second Receiver (RX2) is, in fact, an entirely independent software defined radio receiver that is equal in performance to the outstanding receiver found in the FLEX-5000 family of software-defined transceivers. With an incredible third-order dynamic range of ~100 dB in extremely close spacing (less than 2 KHz), the FLEX-5000 with the RX2 installed results the most versatile multi RX transceiver available. Future enhancements to FlexRadio PowerSDR will exploit these capabilities to their fullest producing a truly "single box" SO2R solution. The RX2 achieves its ultra-high performance characteristics by utilizing independent signal paths, filter banks and direct digital synthesizers (DDS) so that there is no compromise in the receiver design.Utilizing the multi-RF path switching matrix that is afforded by the new upgraded HRFIO (assembly #34), the FLEX-5000 can be configured in any number of different ways to best match your operating style and environment. The independent FLEX-5000 second receiver can be assigned to its dedicated receive only port (RX2 IN), the RX1 tap (defined by the antenna ANTx port used by RX1) or assigned the ANT1 transceiver antenna port. That means you can operate with two different antenna/amplifier combinations on two different HF bands to achieve SO2R operation in the same radio. No more cobbling together multiple radios and messy interfaces to achieve SO2R capabilities. FLEX-5000 transceivers that are equipped with the original HRFIO board (assembly #27) do not have the ability to assign an antenna to a transceiver port. In this configuration, the RX2 can only be assigned to RX2 IN and the RX1 tap. The RX2 integrates into the full duplex design of the FLEX-5000 to create a genuine triplex transceiver capable of cross band operation. The many antenna connector combinations are only the beginning of the capabilities afforded by the RX2 when combined with FlexRadio PowerSDR, the SDR control software. State of the art, never before offered reception capabilities such as frequency and phase-locked spatial diversity reception to mitigate the effects of fading and to enhance the signal-to-noise ratio will be tools the amateur radio operator can use to pull in the weak ones. With the proper antenna configuration, polarization diversity can be achieved too with dual synchronous receivers. Preferred receiver selection can enhance diversity reception techniques by having the FlexRadio PowerSDR software determine which receiver signal is the strongest or has the highest signal to noise ratio and automatically routing that audio to the AF output.†Diversity reception techniques are not the only capabilities the RX2 can provide. Adaptive interference cancellation/elimination to remove unwanted QRM in the passband will be available to amateur radio operators in a future release of FlexRadio PowerSDR. There are also the facilities to monitor your actual transmitted signal using the second receiver in real time.

FLEX-VU5K Module

The FLEX-5000 V/U upgrade module (FLEX-VU5K) is a fully integrated all-mode, all-band full-duplex VHF/UHF module that adds both 2m and 70 cm capabilities to the already outstanding FLEX-5000 family of software defined radios. The FLEX-VU5K module transforms the FLEX-5000 into the ultimate satellite or terrestrial weak signal transceiver with enough RF output (60w) on both bands to drive high power V/U amplifiers. Or you can run it in low power mode with its 50 mW output that can drive a wide variety of external transverters for microwave operations. The FLEX-VU5K module's oscillators are locked to the 500 MHz master oscillator in the FLEX-5000, which in turn is locked to the internal 0.5ppm reference or it may be connected to an external 10 MHz reference, such as a Rubidium clock or GPS disciplined oscillator for even greater frequency stability and accuracy.

FLEX-VU5K Module Features and Specifications:

  • Frequency Range: 2m (144-148 MHz) and 70 cm (430-450 MHz)
  • Low noise preamp: 1 dB NF
  • Frequency stability: ± 0.5 ppm (internal) or greater using the external 10 MHz reference
  • Both V/U oscillators are locked to the 500 MHz master oscillator in the FLEX-5000
  • Class AB biased power amplifiers
  • 60 watts on both VHF and UHF
  • PA RF bypass (50 mW output) for transverter operation
  • All mode support - supports SSB, FM, FM-N, CW and digital modes (ASFK)
  • Full duplex cross band operation mode - Satellite ready: B and J modes supported
  • Simplex operation mode.
  • Same band split operation for FM repeaters
  • CTCSS encode for FM repeaters and LEO satellites (PowerSDR v2.1).
  • Separate dedicated antenna connectors for VHF and UHF.
  • Internally installed in the FLEX-5000

NOTE: The HRFIO-34 RF switching matrix is required to utilize the FLEX-VU5K module. Refer to the following Knowledge Center article, to determine if you need to upgrade your HRFIO board.


Automatic Tuning Unit upgrade for FLEX-5000A and FLEX-5000C. The FLEX-5000-ATU is an optional integrated state-of-the-art, processor-controlled switched-L tuning network for the FLEX-5000 that provides fully automatic antenna tuning across the entire HF range including 6 meters. It will tune dipoles, verticals, Yagis or virtually any coax-fed antenna over a wide impedance range. Tuning functions are fully integrated into FlexRadio PowerSDR for ease of use and operation.
ATU Features and Specifications:

  • Continuous coverage 1.8 to 54 MHz
  • Power rating (1.8 to 30 MHz): 5 to 250 watts (100 watts on 6m)
  • Integrated with FlexRadio PowerSDR
  • Over 16000 memories for instantaneous band changing.
  • Tuning time: 0.5 to 6 seconds, <0.1 second memory tune
  • Tunes 6 to 1000 ohm loads (16 to 150Ω on 6M).
  • For Dipoles, Verticals, Vs, Beams or Coax Fed Antenna.


All RF connections on FLEX-5000 models are made through a rear panel board called the HRFIO, also abbreviated as the RFIO board. The FLEX-5000-HRFIO (Assembly #34) is an upgrade to the original HRFIO board that adds new features and capabilities to the FLEX-5000 especially when used in conjunction with the RX2 or the internal VHF/UHF Upgrade Module.
HRFIO-34 Features and Specifications:

  • ANT 1-3 are defined as transceiver ports (RX1 and TX).
  • A dedicated RX only antenna connector for RX1 (RX1-IN).
  • A dedicated RX only antenna connector for RX2 (RX2-IN).
  • The ability to have RX2 tap off of the RX1 signal path post the RX loop (RX1-TAP).
  • Separate input and output for the 28 MHz IF used by external transverters.
  • A common input and output for the 28 MHz IF used by external transverters.
  • The ability to connect RX2 to the ANT-1 UHF connector for transceiver operation (SO2R)
  • The ability to create an RX only "loop" (output/input) for inserting RX only devices in the RX1 signal path.

Note: For SO2R operation using the RX2, the ASSY 34 HRFIO is required so that you can assign the transmitter (TX) to ANT1 along with the RX2.All FLEX-5000 transceivers shipped after April 2008 already have the HRFIO-34 installed by default. Please check your HRFIO assembly number before purchasing. Please refer to the KC article for instruction on identifying the HRFIO board installed in your FLEX-5000.

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