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Multi-Rx Card

Enables general coverage reception from 2-30 MHz
(An all-band replacement for the band-specific RXAMP module)


Measuring just 2.6" x 1.8", the Multi-Rx card fits neatly on the SRBase Board

 in place of the RXAMP to provide bandswitched general coverage receive

 from 2-30 MHz, with gain and attenuation stages controlled

by the existing cable in the SDR Cube.



The Multi-Rx Card is a 2-30 MHz bandswitched filter+gain board that provides "general coverage" reception for the SDR Cube in the 2-30 MHz HF spectrum.  No more need to open the Cube's case to replace the RXAMP module when you want to listen to (or operate on) another band!  The Multi-Rx card replaces the need for individual RXAMP boards to be plugged in for the desired range, and will be the default board shipping in all new SDR Cube orders going forward.

In addition to the same attenuation and gain stages as before on the RXAMP module, we provided four switched bandpass filters (BPFs) that are controlled by the DSP card over a new 2-wire cable that plugs in conveniently next to the existing Attenuation control cable (also coming from the DSP card).

Only one small mod is required on the SRBase board to accommodate the new Multi-Rx card.  The Cube owner must simply move the C30 coupling capacitor to another pin on the TXPA connector in order to bypass the TXPA filtering path and get the full-strength receive signal.  See the Modification section below that details this small modification.


The Multi-Rx card is shown here installed on the SRBase Board next to the TXPA module, plugged into the same two SIP connectors as previously used by the RXAMP module.


All documentation has been updated to detail the cabling and construction of the Multi-Rx card.  Just check out the normal locations for these documents and instructions.


The Multi-Rx card architecture is essentially the same as that of the RXAMP, but with four Band Pass Filters (BPFs) on the card and selected by an additional two lines coming from the P13 Band Switch connector on the DSP card.  These two extra lines are brought to the Multi-Rx card by a new Cable #9, which plugs in alongside the Attenuator control Cable #8 into the P102 pinheader, as shown in the schematic below.

These two new Band Switching signals on P102 pin 5 and pin 6 control CMOS switch IC1 in order to connect the appropriate BPF for the given frequency that the Cube is dialed to.  The BPFs are designed for the same frequency bands as were the four individual RXAMP modules: 2-4 MHz, 4-8 MHz, 8-15 MHz and 15-30 MHz.  Refer to the filter curves in the next section to see the individual response curves.

The rest of the circuit operates as before with the RXAMP. The RF input signal at P100 is applied to a two-stage attenuator pad (6 dB and 10 dB, respectively), as controlled by the Attenuator control cable from the DSP card (through relays RLY1 and RLY2) also plugged into P102.  Then, after the signal is attenuated (or not) and passed through the selected BPF, the signal undergoes a 24 dB amplification in Q3 before being applied to the SRBase board for mixing with the Cube's VFO and further signal processing.

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Magenta: 2-4 MHz
Green: 4-8 MHz
Red: 8-15 MHz
Blue: 15-30 MHz



Board Interconnect


The Multi-RX card fits neatly on the SRBase board in the RF compartment of the SDR Cube, as pictured below.

The same 4-wire cable for Attenuation control connects to the Multi-Rx card's P102 connector at the bottom/right end. 

And the new 2-wire cable connects the bandswitching signals from P13 on the DSP card to the same P102 connector on the Multi-Rx card.


C30 Modification on SR Base Board

It is necessary to make a small modification to the SRBase board to allow the receive signal path to reach the Multi-Rx card without going through the TXPA module's BPF.  (The TXPA filtering would be interfering with the signal for frequencies outside that TXPA module's range.)

This rerouting of the receive signal path can be done by:

    1) On the top side of the SRBase board, cut the trace just above the C30 capacitor that goes to J2 pin 5, using a sharp razor blade.

    2) On the bottom side of the SRBase board, add a jumper from J2 pin 1 to the top pad of C30, as shown in the lower-right photo below.


                                                                                SR Base Board
                        (Top)                                                                                                      (Bottom)



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Page last updated:  January 2014