N9EWO Guest Review :
Burkhard - Reuter RDR55E
SDR Communications Receiver

Burkhard - Reuter RDR55E SDR HF Receiver. (Dean Bianco photo)

N9EWO : Dean Bianco provides a guest review of the Reuter RDR55E HF SDR receiver. Our thanks to Dean. Excellent information on this German designed and built SDR receiver. No fans to disrupt listening with the configuration as tested. Built in world voltage switching power supply. Option module available so can be used as a 5 watt HF QRP amateur radio transceiver (not tested). The approx. $ 675. RDA31B OPTION module is REQUIRED for fixed audio line audio output (not tested). Base price in the $ 5100. USD area (final price dependent on options). 

Approx. Serial Number of Test Sample  : 085 (manufactured in November 2021)
Firmware Version(s) Tested :
EV 631

Options Installed :
RDR35D GPS / DSP Module

Dean Bianco user guest review of the Reuter RDR55E.

The RDR-55E is a high-end, stand-alone SDR receiver (can be used as a QRP transceiver as an option, not available in the review radio) covering a frequency range of 1-30 MHz and, in the review unit, 50-54 MHz.  The FM Broadcast Band and the 2 Meter Ham Band (87.5-108 MHz and 144-148 MHz, respectively) are available as options, not available in the review radio.  The receiver is built in small batches by the German firm of Reuter Elektronik, led by the electronic engineer and fabricator, Burkhard Reuter. This stand-alone model is ideal for those users who prefer not having to engage a computer, monitor, keyboard, and mouse as is normally the case for many SDR's.  Employs a touch-screen panel to access all of the tuning parameters. Only one large weighted knob.

The following is an overview of the test sample I own:

Test Model: RDR55E2 firmware version EV 631
Serial Number: 085
Build Date:  November 2021
Dimensions:  (W) 11.42 in  x  (D) 9.65 in  x  (H) 5.91 in-----(W) 290 mm  x  (D) 245 mm  x  (H) 150 mm
Weight:  Varies depending the number of modules installed.  Test unit weighs approximately 12 lbs (5.44 kgs)
Operational Theory:   Proprietary time-based and spectrum-based, direct-conversion processing scheme.  

Receiver Case:  A heavy-gauge main frame chassis with a bus board that employs up to 9 rear-mounted pluggable modules, depending on options.

Case Materials:  Anodized, extruded aluminum top and bottom covers.  0.2-inch machine milled side panels.  Rear panel contains plug-in modules for various functions and options.  The modules are constructed of heavy-gauge aluminum. Rubberized tip-up feet.  The radio can be built to your choice of black or grey powder-coated color.

Display: TFT WVGA 5-inch diagonally-measured, 512 colors, fully adjustable brightness. Takes very little finger pressure to activate.

Digital Architecture:  (for tested unit) 2 x ADC's in push-pull 17-bit, Cyclone V FPGA, direct digital conversion.

Modules: (as installed in test sample):
RPS30D-- 110/230 volt 25 VA consumed, no cooling fan used in test sample.
RAD17D-- A/D converter, RF deck.
RDR35D-- DSP software, GPS-disciplined oscillator, WI-FI for WLAN.
FDA21-- Audio Card.
All modules are heavy-gauge anodized aluminum.

Input Connectors:
- SMA for receive antennas
- SMA for GPS antenna.

Radio comes with an SMA-to-BNC coax jumper cable, touch-screen stylus, GPS antenna with coax cable (if GPS option is installed), Wi Fi antenna.

Tuning Encoder:  High-quality steel rotary optical encoder w/ finger dimple, smooth tuning w/ no detents. Optional magnetic encoder w/detent tuning (not tested).

Power Requirements:  Choice of either a built-in 110/230 volt switching-mode power supply, which uses <25 va in full operation, <1 va in standby, or a user-supplied 13.8 volt external power supply.


Adjustable Tuning Steps:  Any step from 0.5 Hz to 100 Khz via the keypad, or in fixed steps from 1Hz, 10 Hz, 100 Hz, 1 kHz, 4.5 kHz, 5 kHz, 8.33 kHz, 9 kHz, 10 kHz, 12.5 kHz, 25 kHz, 50 kHz, and 100 kHz for all modes.

Frequency display reads out to the nearest 1/2 Hertz (yes 0.5 hertz !) Main oscillator stability +/- 1 ppm.  GPS option stability is exactly 1 Hz (tested).

Adjustable variable speed tuning, defeatable.
Modes spectrum-based: SYNC (w/selectable sidebands or DSB), USB, LSB, DSB w/o carrier, CW.

Modes time-based:  AM-Envelope, FM-N, FM-W, DIGI (optimized settings for user-supplied modem decoding of digital modes), analogue-emulating DSBQ, LSBQ, USBQ for when extremely low latency, constant group delay, lowest distortion are required and/or fed to a PC sound card or speaker.

Variable bandwidths from 40 Hz to 20.32 kHz, mode-dependent:

Selectable bandwidths by mode:
           AM-Envelope---from 3 kHz to 20 kHz---in progressive 500 Hz/1 khz/2 kHz increments.
           AM Synchronous DSB---from 80 Hz to 20.32 kHz---in 80 Hz increments.
           AM Synchronous LSB/USB---from 80 Hz to 10.24 kHz---in 80 Hz increments.
           DSB (no carrier)---from 80 Hz to 20.32 kHz---in 80 Hz increments.
           LSB/USB---from 80 Hz to 15 kHz---in 40 Hz increments.
           CW---from 80 Hz to 1.6 kHz---in 40 Hz increments based on a pitch setting of 800 Hz.
          (Bandwidth increments differ dependent on a pitch setting other than 800 Hz which were untested)

           USBQ/LSBQ---from 1.5 kHz to 10 kHz---in progressive 250 Hz/500 Hz/1 kHz increments.
           DSBQ---from 3 kHz to 20 kHz---in progressive 500/1 kHz/2 kHz increments.
           FM/W---fixed steps of 38/50/60/80/120/250/300 kHz.
           FM/N---from 3 kHz to 20 kHz in progressive 500 Hz/1 kHz/2kHz increments.
           DIGI---from 125 Hz to 4 kHz in progressive 250 Hz/1 kHz/2 kHz increments.

- PBT in all modes except time-based.
- Notch filter in all modes except time-based.
- Dynamic noise reduction in all modes except time-based.
- Two-step noise blanker in all modes except time-based.
- RF squelch threshold, all modes.
- AGC limit, AGC hold and AGC attack constants in all modes.
- Audio filtering from 20 Hz to 15 kHz continuously.

- Selectable surround-sound feature aids in weak-signal audio recovery.
- Spectrum display with variable refresh speeds, adjustable dBm increments.
- Waterfall display, 16 colors. (Untested)
- 199 memories. (Untested)
- 20 dB attenuator, nominally.  Works in concert with the RF preamp to adjust attenuation level.
- RF Preamp 15dB
- Built-in preselector/RF filters.  Adjustable.  Defeatable.
- Built-in, front-firing speaker 2 watts output.  External speaker(s) can be effectively fed from the headphones jack.
- Front-mounted 1/8 inch headphone jack.
- Independent controls for the speaker and headphones audio.
- S-Meter reads in dBm, dBu, and S-units and features separate peak-signal readings.
- Optional GPS module which calibrates the frequency stability continuously to 1 Hz accuracy, displays time in UTC, displays longitude and latitude, altitude above sea level, satellite ID and SN/R, and receiver clock deviation in Hz. (Tested)


The following was based on my personally-owned RDR-55E fed by a 122-foot long T2FD antenna with the high point 50 feet above ground, fed with quality RG-8U coax cable, no signal processing accessories, in a quiet rural receiving post.

OVERALL AUDIO:  Superb audio, especially with an external speaker(s).  Rich fidelity benefits strong and moderate signal levels, yet pleasingly very effective in aiding weak-signal recovery, to my ears.  Enhanced signal recovery when judicious use of PBT, AGC, and DNR are engaged. I use Bose Companion 2 Series III speakers with excellent results.  The audio quality exceeds that of my WJ-8711A.  The lower distortion is noticeable.  I formerly owned a Flex 6400M transceiver which had excellent to superb audio, but the RDR-55E is better still.  The bass frequencies are smooth and warm sounding, never muddy (unless using a very narrow bandwidth, of course).  The mid-range and treble is crisp enough.  I prefer a wide range in audio recovery, and if you use a quality external speaker, you can appreciate the subtle differences of the highly customizable audio frequency range.  I notice less of a "digital sound' to the overall audio in most bandwidths as compared to other DSP-based receivers.  However, for those times when a clear signal is present, there is a time-based demodulator that produces a near-tube-type audio experience with AM and SSB. 

PASS BAND TUNING:  Available in all modes (except time-based) and it works well.  Works superbly to avoid adjacent-frequency interference and for tone contouring.  No digital artifacts or circuit whine when adjusting the settings, as is the case in many modern receivers.

RF BANDWIDTH SELECTIVITY:  A plus for the RDR-55E over most receivers---SDR or otherwise---is the very wide bandwidth filtering.  It ranges, depending on the mode in use, from 80 Hz to 20.32 kHz, fully adjustable in 40 Hz steps via the main rotary encoder, all done in a seamlessly smooth and fast maneuver.  Theses widths, however, are mode dependent.  For instance, when tuned to a station in lower or upper SYNC mode, the widest bandwidth is slightly over 10 kHz wide.  Not a complaint as this makes sense as the effect is the same as when DSB SYNC is set to 20kHz.  LSB and USB tune out to 10 kHz maximum and CW goes out 1.6 kHz maximum.  While I have no test equipment in my listening post, I can only go by what my ears tell me:  the selectivity of these DSP filters are razor sharp and are the equal of the WJ-8711A, known for its sharp filter shapes.  If softer audio emulating analog sound is desired to reduce digital latency for critical digital or SSB use, you can switch from standard spectrum-based demodulation to time-based demodulation in AM, LSB/USB, DSB, or DIGI modes where less brute-force filter shape is not desired or required.  Another plus is the lack of noticeable ringing in narrowest of CW filters, to my ears.

SENSITIVITY:  Again, I go by my ears as I do not have any test equipment, but the RDR-55E's sensitivity is not an issue at all.  I compared the sensitivity to the WJ and to an NRD-515, known for its high sensitivity.  All three receivers were equal in signal strengths at the weakest levels.  I did my best not to allow audio recovery to influence the results.  All three were equal with no discernible winner.  However, I had to turn off the Reuter's built-in preselector on frequencies above approximately 17 MHz in order to amp up more sensitivity lost by having the pre-selector engaged. The 8711A has a pre-selector, but it had no loss of sensitivity whether engaged or not at these higher HF frequencies, unlike the noticeable difference with the Reuter.  But I should emphasize that this was a very small difference, and of course these were tested with very weak signals.

SYNCHRONOUS DETECTION:  Whether used in the DSB mode, or the LSB/USB selectable mode, fading-distortion in the audio recovery is completely vanquished.  Its ability to maintain lock on rapid, deep fades and on weak signal carriers is superb.  When used in the selectable-sideband mode, adjacent interference was reduced or eliminated on several test stations.  This is a true winner.  It compares favorably to the old Sherwood SE-3 in terms of audio quality, shaping, and interference rejection.  It very slightly outperforms the Flex6400M when it comes to AGC smoothing of rapid fades, and that radio has a damn good sync detector.  The WJ has a worthy sync detector, but it is only DSB, not sideband-selectable, and that is a considerable drawback when conditions call for adjacent channel interference reduction.  Also, the WJ's sync can occasionally lose lock.  I also had at one time the superb ICOM R-8600 and its native sync detector, in my findings, is a real dog, so no fair comparison there.   I have yet to find a signal that has made the Reuter's sync lose lock!  It's the best I have experienced so far and neck-and-neck with the Sherwood SE-3.

SPECTRUM SCOPE:  The 5-inch diagonally measured spectrum scope is well-designed, crisp and uncluttered in appearance.  I have mine set to 160 kHz end-to-end bandwidth and set so that the speed of the real-time spectral signal lines are moderately smooth in action, although these parameters are adjustable to your taste and requirements.  By choice, I have very simple requirements for my spectrum display.  I merely use the display to see adjacent signals near my target signal, and select a signal blip and tune in that way.  Others may prefer deeper analysis of signal modulation peaks and other such data.  Even though I have not much need for the spectrum display other than what I describe above, no doubt many of you will love the great detail of signal analysis provided by this top-notch spectrum display.  NOTE: The RDR-55E features a 16 color, full-featured waterfall display.  It cannot be run concurrently with the spectral display, as designed by the  manufacturer. I did not test the waterfall as I have no interest in it.  The display, when I observed it briefly to make sure it works, appeared to be adequate.

STRONG-SIGNAL HANDLING:  The dynamic range seems to be very robust.  I have yet to find any intermodulation, cross-modulation or strong-signal overloading, with or without the 15 dB pre-amp engaged.  I tested it against a 75 db over S9 (+ 5 dBm!!) medium wave signal from a temporary location 2 miles from at 10 kW of power.  No attenuation engaged.  Not a blemish in reception quality to my ears.  I was blown away by this.  My WJ has a great dynamic range with strong signal levels, but at +5 dBm the WJ showed some noise artifacts.  Impressive!  Unlike other SDR's, such as the high-quality super-performing ICOM R-8600, the RDR-55E has no overload indicator.  Perhaps because it doesn't need one.

PHASE NOISE:  According to the manufacturer's specifications and the WRTH's test equipment, the phase noise is purported to be better than -140 dBm.  My ears tell me that extremely weak signals adjacent to very strong ones do not get "de-sensed" by the stronger signal's presence.  The RDR-55E has the quietest apparent noise floor than any other high-end receiver I have owned, namely the WJ-8711A, the R-390A and the NRD-515.  I had barely-usable audio recovery from the BBC on 9410 kHz at a very low signal strength of -134 dBm with the Reuter whereas the WJ was slightly less useable and the NRD produced only mud.  Impressive.

AGC:  The AGC is very flexible in terms of hang-time, attack-time, and limit settings.  Unlike many receivers, the RDR-55E requires one to make frequent adjustments in order to obtain the best audio recovery under all kinds of reception conditions be they easy-listening or rife with fluttery, atmospherically-noisy, or interfered-with signals.  This cannot be understated.  A long AGC hang-time can smooth out most if not all of the fluttery signals one encounters from signals affected by solar activity and by polar path absorption.  Sometimes a short hang-time reduces the effects of audio drops on those stations which have low modulation.  We also have adjustable AGC attack-time settings.  The RDR-55E's is highly effective in reducing pumping and eliminating syllable-onset popping or clipping distortion that is the bane of radio hobbyists who use receivers with poorly-engineered AGC circuitry.  Also, judicious adjustment of the attack setting can tame background static crashes, man-made transmitter splatter, and an aggressive ionosphere.  This is not a "one-size-fits-all" or "set-and-forget"  AGC.  I for one love this level of adjustability, but your preferences may differ.  Keep this in mind if you are thinking of obtaining an RDR-55E.

NOISE BLANKER:  This is the thorn in the rose that is the RDR-55E.  It simply does not work.  At ALL!!!  Inexcusable on a state-of-the-art, DSP-based communications receiver.  It should be noted that I have spent hours adjusting all of the settings, in combination with other reception aids such as PBT, DNR, AGC, etc in order to get it to blank any pulse-type noise that it is designed to reduce or eliminate.  My hours proved fruitless.  Now, in all fairness, when I contacted a Reuter associate, he informed me that the reason for my finding the NB function inoperable might​ have to do with my North American 60 Hz line frequency vs the 50 Hz line frequency found in Europe and in much of the rest of the world.  I was told that Mr Reuter would be made aware of the issue and that it would be a matter of a firmware update to resolve the issue.  I for one cannot wait until that happens.  If and when it does, I will amend this review.

DYNAMIC NOISE REDUCTION:  If the NB is the Achilles heel of this radio, the DNR function is the icing on its cake!  The effect is excellent in reducing white noise from the audio path.  Voice and music equally are rendered very natural even when the DNR is set to a well-advanced level.  The only time digital watery effects come into play are when the setting is up to its second-to-last and highest reduction strength.  I found the last setting only useful on those occasions where the quality of the audio is secondary to the need to recover intelligibility under harsh noise conditions.  Particularly satisfying is its ability to reduce by leaps and bounds the tiring hiss of white noise from weak-to-moderate signals.  I found it reduces the edge of crackly static crashes adequately.  Overall, it's flawless.

ATTENUATOR AND PRE-AMP:  We have 0 db, 5 dB, and 20 dB settings of selectable attenuation from which to choose.  We also have a selectable 15 dB preamp at our disposable.  Although I could not find ANY occasions where the attenuator was needed, I like to reduce the noise floor and signal intensity of the MW band at night.  Unlike some pre-amps on other radios, it does not cause any signal overloading, cross-mod or other weird behaviors.

RF THRESHOLD (SQUELCH):  Adjustable in dBm increments. This generally works quite well and in all modes.  It does however have a flaw, in my observation.  In some circumstances, the initial signal rise that breaks the silence of an engaged squelch cuts off a second or two of the content of that signal.  Yes, I was mindful of all the settings and adjusted all variables continuously, but to no avail.  Again, not under all circumstances.  Oh well.  It's not really that big of a deal to me---but it may be to you.  On the plus side, when signals fade below the RF threshold setting, the hysteresis effect allows a temporary suspension of the absolute threshold setting so that the audio allowed to pass doesn't get chopped up and deleted during a fading signal as it gets under the threshold barrier.  Nice!  The squelch on the WJ is also superb, but it lacks hysteresis.  The only squelch I have used that overall is better implemented is the one on the ICOM R-8600.

BUILT-IN SPEAKER:  The speaker produces a high audio range and is adequate under many circumstances.  My last SDR radio was the Flex6400M which also features a built-in speaker.  It was an absolute joke.  Weak, thin audio that requires the speaker volume to be turned up to more than 3/4 of the way.  Thankfully, nothing at all like that with the Reuter's built-in speaker.  However, as good as it is, it is not stellar for my taste.  As such, I use Bose amplified speakers to allow the rich and  powerful audio to shine through that the RDR-55E is capable of producing.  

HEADPHONE USE:  High-impedance headphones allow ample volume without hum or buzzies or other audio weirdness to come through.  Other radios usually have some deficiencies in headphone-delivered audio.  Not so with the Reuter.  Excellent.  I use quality Sennheiser phones for best fidelity.

MAIN TUNING-ENCODER KNOB:  The knob is made of quality, weighted steel and contains a finger indent for super smooth tuning.  It never binds, never slops over.  The action is consistent whether you are slowly fine tuning a signal in or rapidly tuning across a band.  There is a variable rate tuning setting that can be set to various levels of speed-increases the faster you tune the knob.  This feature is offered or in the past had been offered with other receivers, with varying success.  This is my first time having a radio that offers it.  I personally love it as it reduces user fatigue when doing a lot of hands-on back and forth scanning the bands.  This VRT works well in my findings.  Some of you may not like this feature---at all.  In that case you can leave it disengaged.  Also, it should be noted that there is no electronic tuning knob lock feature.  Perhaps in a future firmware upgrade, one can be implemented, as mentioned by the Reuter associate when I suggested it to him.

SCANNING FACILITIES:  None!  No scanner built-in as it was designed.  I wish it had it but oh well.  You might think otherwise, so be aware.

RECORDING FACILITIES:  None!  Ditto the above!!!

MANUAL:  Available only as a pdf on line at the Reuter-Elektronik website.  I printed one out in full color and placed it in a spiral bound binder, which I vastly prefer over having to stare at a pdf on a computer or smartphone.  BTW, the manual is not stellar.  It is confusing.  While generally well-translated from German into English, it is overly long, it is not in build-version order and needs some editing to remove German screenshot captions and to remove older versions with different screen appearances, and obsolete features.

In conclusion, the Reuter-Elektronik is a turbo-charged hot-rod among modern SDR-based receivers, in terms of sheer performance and build-quality.  It is now my go-to receiver for down-and-dirty and long-term listening sessions.  It is one of those rare type radios that excels at DXing and easy listening, and does so without sacrificing one aspect over the other.  The downside is cost.  It is very expensive and rather difficult to obtain outside the EU.  Of these two, obtaining one is much less an issue than having the money to buy one!  Fortunately, there is a work-around in purchasing one outside the EU.  Inquire at the website about how to get one.   It is a winner in many regards.  I am very pleased with it and I feel confident that you be, too.

Dean Bianco
© all rights reserved
ver 1.4

RDR55E General Specifications
- 7" (178 mm) WVGA display 800 x 480 pixels with touchscreen (matt surface)
- Latest audio hardware with spectrum-based and time-based DSP
- Optical encoder without detent, optional magnetic detent
- RPS30: Power supply 90 ... 230 V ~ 30 VA, external supply 12.3~14.4 VDC possible
- RAD18E: 18 bit ADC (4 ADC units 16 bit), automatic 2-channel preselector on MW / SW, FM, 2 m (130 - 156 MHz), DAB +, remote control of RLA4 / RFA1
- RDR35D: DSP module with t/f converter 2.5 Hz frequency resolution, GPS, WiFi, Bluetooth
- Free software updates independent of device and owner
- 11.42 in x 9.65 in x 5.91 in (290 mm x 245 mm x 150 mm) (length / width / height, tip-up feet folded)

- Weight depending on options up to approx. 6 kg (13.2 pounds)
- Aluminum extruded section for top and bottom cover, AI 0.2 inch (5 mm) thick milled side elements
- Special conductive surface finish (Chromium IV, RoHS-compliant)
- Powder coated external surfaces, anodized front panels
- Bus board with 11 slots (2 in the front, 9 in the back)
- Plug connectors: 68-pin (62 used) “SCSI” standard 0.05 inch (1.27 mm) grid shielded
- Board size of the back-mounted modules 0.183 x 0.124 square inch (118 x 80 mm) (RDR54 compatible), 0.183 x 0.163 square inch (118 x 105 mm)
- Visible front panel height 4.92 inches (125 mm)
- Rubberized tip-up feet, approx. 1.19 inches (30 mm) lift-able in the front
The other specifications for the RDR55 are the result of the used modules and the software. Please consult the current documentation.

Reuter RDR55E's Touch LCD and Spectrum Scope (Dean Bianco Photo)

Any buyer must keep in mind that the RDA31B OPTION module is
REQUIRED for fixed audio line audio output (unbalanced 2 RCA phono jacks).
This 590 Euro (about $ 675. USD) option was not installed in the test sample. (manufacture photo)

Reuter RDR55E Test Sample Off Air Recordings
  (as recorded via it's front panel headphone jack - Sangean DAR-101)
MP3 Format / 56 kbps

- BBC Sync - LSB (medium strength signal)
- 80 Meter Amateur LSB with DNR on
- Voice of Greece 9420 kHz Sync USB Bandwidth 10 kHz
- WRMI 7780 kHz Sync Bandwidth 8 kHz
- WRMI Sync DSB Bandwidth 10 kHz
- Radio Romania International 7325 kHz Sync DSB Bandwidth 12 kHz

Rear view of a RDR55E with the OPTIONAL RDA31B audio line out and RDR35D GPS / DSP modules.

Links for additional Information (all subject to change without notice) :

Fenu's Review of the Reuter RDR55D HF Receiver

Fenu's Review of the Reuter RDR50B HF Receiver

Reuter RDR52 - Fenu Radio "You Tube Video"

Burkhard - Reuter RDR55 Web Page

Operator Manual RDR50/54/55 (PDF)

eham Reviews : RDR50 B4 qrp-transceiver with VHF-option

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