SDR Panadapter

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Station Improvements

During the IARU HF Championship contest in July I was talking with Stewart GW0ETF and Steve GW0GEI about their use of Flex radios. They really convinced me of the value of being aware of an extended view of the band during contests and to track where DXpeditions listen in the pileups.

I also knew Chris G3SVL had recently used a FUNcube SDR as a Panadapter, so after a helpful email exchange I copied Chris’s set up to see what I’d been missing.

Here's the equipment setup.

I use a laptop so it’s useful to use a USB hub to keep the cables out of the way. The hub isn’t needed as long as the CAT and FUNcube plug into the same PC. The FUNcube is a very capable receiver in its own right. It has a tuning range from 150 kHz to 240 MHz and 420 MHz to 1.9 GHz. Here it is used simply to sample the IF of the K3 centred on 8.215 MHz, and up to 192 kHz can be displayed.

The Software

There are two free software packages that get this all running.

LP-Bridge or LPB2 work with Elecraft, Yaesu and Kenwood radios, and all SDRs with IQ outputs or integral soundcards. LP-Bridge connects the K3 CAT data and the SDR data stream to NaP3 and any logging programmes. It does this by creating virtual COM ports and intelligently routing serial traffic between the K3, the SDR and up to 5 other applications.

Displays and demodulates the SDR digital data. It can also control the K3 VFOs, filters, bands and modes. This is where the SDR flexibility really comes into its own. By dragging the spectrum with the mouse it is easy to get to within a few hundred Hz and then use the mouse wheel or tuning dial of the radio to net CW or resolve SSB.


NaP3 can also connect to the DXCluster and callsigns are displayed above the spectrum display (see below). Clicking on a callsign in the spectrum window sends the radio to that frequency.

RBN Telnet servers & Skimmer

Reverse Beacon Network servers and local or online Skimmer servers can feed CW and Data spots to the spectrum display.

Logging Software

The logging software runs as normal to the rig but via a virtual port on LP-Bridge. For example one application could be Logger32 on one COM port and N1MM on another port. I’m looking forward to seeing how this all works on the next big DXpedition pileups.

Other Options

There are many other SDRs and software packages that can be used. I haven’t tried them but they are worth investigating. The LP-Pan and the Elecraft P3 would work just as well. Though it can be done a lot cheaper. Here is a good example of a $20 RTL SDR connected between an FT857 and HDSDR, using Omnirig for the CAT. It’s a very low cost system and provides a big improvement over the performance of the FT857 alone, adding powerful abilities to filter and add noise reduction.

NaP3 and the K3

NaP3 processing of the FUNcube sound card data can also add noise reduction and noise blanking to the demodulated audio of the laptop that is entirely different to the DSP in the K3 (e.g., more effective noise blanking with a wider bandwidth). This can offer a different listening experience. On the other hand the K3 with second receiver and two antennas can offer true diversity reception which is a much more robust listening experience with polarisation and spatial diversity.


1. SDR Sharp

2. Using the RBN


4. Power SDR

5. SDR-radio

6. RFspace

Click or tap on a thumbnail to see the big picture.

40m SSB in the 2015 IOTA Contest.

40m CW in the 2015 IOTA contest.

OTH radar (Cyprus I guess) drifts into the middle of 20m during the IOTA contest. This cannot easily be identified when listening on SSB with a 3kHz filter, but it’s obvious on the panadapter.

Aligning the FUNcube

The FUNcube has settings to enable/disable the LNA, the mixer gain and apply a gain offset.
These settings were used to calibrate and optimise the performance as follows.

The LNA is enabled for best Noise Figure and lowest noise floor. The Mixer gain is turned off to achieve highest possible spurious free dynamic range, with this setting there are no visible spurs. The IF gain is set to 0dB as any more gain does not improve the sensitivity of the ADC and only serves to reduce headroom and dynamic range.

The K3 was fed with a signal generator and attenuator at a level of -57 dBm. The K3 signal level was set to read in dBm.

The Level offset was then adjusted to make the signal meter display -57 dBm. This required an offset of +9.3 dB.

Job done, accurate level display with low noise floor and no audible or visible spurii.

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