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SDR Cube Transceiver

Portable, standalone SDR transceiver for SSB, CW and AM using embedded digital signal processing
with a Softrock as the RF front end for QRP operation. Live bandscope, high-performance T-R switching,
multiple VFOs & memories, General Coverage Receive and bandswitching control are among the many advanced features.
Expansion port supports external RF decks and accessories. Optimized interface for NUE-PSK modem provides digital mode support.


The SDR Cube is a totally self-contained, embedded SDR transceiver for CW, SSB and AM using a Softrock for the RF front end and a pc board implementation of an HF modem.  PC is not needed for using the SDR Cube, as all DSP processing is accomplished by an embedded DSP processor on the three internal pc boards.  The Cube is designed to fit into an optional 4 x 4 x 4.5 pre-cut,black powder-coated aluminum enclosure containing all controls, a blue graphic display indicating transceiver settings and an exciting 8 kHz-wide band scope of spectrum signals, and the popular Softrock RXTX v6.3 board.  The SDR Cube may also be used with any of the 11,000 other Softrocks in the field today!  Sold as a kit or as a fully assembled & tested transceiver, both the product versions are in stock.  We presented on the SDR Cube at TAPR's annual "Digital Communications Conference" in Portland, Oregon, and the DCC Proceedings containing our paper is available in our Documentation page.  Product details are presented here on this website, and active email discussion occurs in the SDR-Cube Group in Yahoo Groups






Click on images for larger views

I/O BOARD                                        DSP BOARD                                            CONTROLS BOARD

The heart of the SDR Cube Transceiver is comprised of three mating PC boards, as shown above.  The board set is designed to conveniently connect to each other by means of edge connectors that may be configured in a number of ways.  When using the optionally-purchased enclosure, the Controls board fits up against the back of the front panel, with the controls and display accessible by the user. The DSP board connects at a right angle to the Control board to sit in along the left side of the enclosure.  And the I/O board connects to the DSP card by means of a short flat ribbon cable to sit parallel to the rear panel.  This arrangement maximizes the space inside the SDR Cube such that one can place a Softrock front end or even a battery in the remaining volume of the enclosure.

The Cube board set may also be arrange in other ways for other enclosures, or perhaps in a flat, side-by-side manner, as we have used in our development arrangements, as shown below ...

Softrock RXTX v6.3 Components

SR-BASE with TXPA and Multi-Rx plug-ins

SDR Cube Transceiver is able to use any of the 11,000 Softrocks in the field today as its "RF front end".  The SDR Cube may be interfaced to the very popular Softrock RXTX 6.3 merely by dropping it into the shielded compartment of the Cube.  Or if the model of Softrock you have doesn't fit, such as the current "Ensemble" series, you may interface it externally with a custom wire harness that connects to the back panel of the Cube.

If you do not already have a Softrock, don't worry!  We have a good supply of the RXTX 6.3 Softrock transceiver kits with the 80m/40m, and 30m/20m/17m plug-in modules available for sale with the SDR Cube.  The Multi-Rx card is standard issue with the full Cube and  Softrock orders.

The Softrock RXTX 6.3 "RF Front End" is an option in the SDR Cube pricing matrix on the Ordering page.

X-LPF ... an "Extra LPF"
An additional Low Pass Filter for use between the Softrock and the antenna
(Click photos to see larger image.)

This is the "eXtra Low Pass Filter" that the Softrock RXTX 6.3 designers recommend using to reduce harmonics when operating on 80m and 30m.  Softrock owners have classically needed to provide this extra LPF in some way for themselves in the past ... but we include it when when SR-Base softrock option is purchased with the SDR Cube.  The X-LPF board dimensions are 1/2" x 1" and it mounts on the back of the BNC connector.  The short RF output cable from the SR-Base board connects over to the nearby X-LPF board and plugs into one of several pinheader connectors, as determined by the band on which one intends to operate: 80m or 30m.  Then a shunt (jumper) is placed across another pinheader to route the RF to/from the BNC connector.  But if the Softrock is going to be used on some other band that doesn't need an extra LPF, the RF cable from the SR-Base gets plugged into another pinheader on the X-LPF board at the RF is routed directly to the BNC, effectively bypassing either of the two extra LPF filters needed for Softrock operation on 80m and 30m.  So again, the X-LPF kit is being provided with all SR-Base purchases.  You do not need to order this item if you already have an SR-Base option ordered; but SDR Cube owners may order the X-LPF item for use with their external Softrocks (see order page for this).  The X-LPF schematic is here.

(BTW, the need for an extra LPF is an example of the Softrock design limitations, not a limitation of the SDR Cube design.  We've previously mentioned some challenges of using the Softrock as our "RF front end", and this is another such challenge.  We are currently building up other RF decks to see how well the SDR Cube performs with a less-compromised design ... RF decks such as the Genesis Radio 2030, WB6DHW's UHFSDR, the FlexRadio SDR-1000, and some others.  Albeit more expensive than the Softrocks, these more encompassing designs have the potential to let the SDR Cube shine with regards to RF performance characteristics.)


Multi-Rx General Coverage Receive Module
Continuous coverage plug-in Rx module covers 3-30 MHz for the receive side of the Softrock RXTX 6.3

(Click photo to see larger image.)


TXPA Plug-in Band Module
A band-specific 1 Watt (typ) RF power amp and low pass filter for the transmit side of the Softrock RXTX 6.3
Kit and assembled version of two modules are available: TXPA-80/40 and TXPA-30/20/17.  
These modules enable the SDR Cube to operate on 5 bands:  80m or 40m  (with the TXPA-80/40 module), or 30m, 20m or 17m (with the TXPA-30/20/17 module)

(Click photo to see larger image.)


Tx Band Coverage
Choose TXPA modules for desired Tx band coverage.
The SDR Cube is able to transceive on 5 ham bands with the correct modules in place, as illustrated below.



Copyright 2014 Midnight Design Solutions, LLC.  All Rights Reserved.
Page last updated:  January, 2018