Just purchased this item Full Band 100KHz 1 7GHz UV HF Rtl SDR USB Tuner Receiver R820T 8232 Ham Radio | eBay from ebay and it all works well exept below 23MHZ i hear no signal..Air noise but no signals at all .Seems as if it's pll is unlocked...Using the sdr sharp software Think it may be a dud? ..Thanks