Archived Spectrum lab window showing KB5NJD CW at 474.5 kHz in addition to weaker WSPR signals mid-band
The KB5NJD “472 grabber” is permanently off line
What is the 472 Grabber?
The “472 Grabber” is very simply, a wide band receiver covering the 630-meter band from 470 kHz – 480 kHz and is comprised of a Soft-Rock Ensemble LF SDR receiver , Soundblaster 96 kHz outboard sound interface, a Low noise vertical with high gain preamp for impedance matching, PC with a lot of head room and Spectrum Lab software by DL4YHF. The entire 630-meter band is processed into a spectrum view for visual identification of signals.
Why do I have a wide band receiver on 630-meters?
The purpose of this full-band receiver is to give an easy and quick view of band conditions and activity on the 630-meter band. Its very easy to get sucked into a myopic view of what is happening in a chunk of spectrum. We all have our preferred modes and areas we like to operate but what is going on in the rest of the band? The band grabber solves this problem. It also gives a means for other transmitting stations to check their station performance.
Where is the 472 Grabber located?
Because co-location of the SDR receiver in the presence of KB5NJD while transmitting would result in a total receiver de-sense and probably a failure of the SDR altogether in short order, it is located at a very quiet remote site approximately 1-mile south-south-west of KB5NJD. As you can see from the screen shot above, even at 1-mile, KB5NJD overloads the receiver. Its a trade off because other sites further away are drastically noisier than the selected location. I compensate by not beaconing at a high percentage transmit cycle.
UPDATE August 20, 2017: The antenna changed today from a PA0RDT E-Probe to a low noise vertical (basically an E-probe with a larger capture area!) with a high gain, high impedance input preamp to perform impedance matching and give a little gain so that the 25 foot long wire can produce usable signal levels. I am using the same pole that was supporting the PA0RDT E-probe to support an insulated wire up the side of the pole. The wire is held tight with a rope and pulley. About 6-foot above ground level, the preamp is mounted with connections to a ground rod and the vertical wire. Power for the preamp is supplied via a home brew bias-T at the SDR and PC. This antenna seems to do well and is less susceptible to environmental noises than the smaller E-probe. It also decreases the wind load on the pole. I am also hopeful that the gas discharge tube on the preamp improves its lightning susceptibility over the long term.