July 28, 2009: KL7UW was added as WD2XSH/45 to the "500-KHz Experimental Group"
  I am getting started setting up a station for 500-KHz (600m) Experimental Group (WD2XSH) and looking at low-noise 
  receiving antennas to use with my SDR to monitor the band.  A Beverage would be 900-foot long which exceeds my
  property boundaries.  An attempt to run a Beverage alongside my neighbor's private aircraft runway did not work out.
  First signals seen with new inverted-L antenna:
  • Screen Capture of 509.6 KHz with 4-KHz span:
  • Screen capture of 508.6 KHz showing WD2XSH/20 CW signal I am also considering building a shielded-loop receiving antenna later on. November 1, 2009: The Inverted-L antenna was raised! The antenna has two wires instead of three for the 130-foot top-hat. The vertical wires are 39.5 feet long with 2.5 feet separating both top and bottom from their supports. Some photos: Here is the NEC4win95 antenna analysis of the antenna: 80 Meter Half Square: 160 Meter Inverted-L: 600 Meter Inverted-L: Table of MFJ-269B measurements of the inverted-L antenna (March 24, 2010):
    SWR/Impedance vs. Frequency
    FREQ SWR Resistance Reactance FWD Power REF Power RF Current Real Power
    495.6 1.8 87 13 22 2 0.5 21.8
    498 1.4 74 0 - - - -
    500 1.2 61 3 - - - -
    501 1.0 53 0 17 0 0.65 22.4
    503 1.1 45 3 - - - -
    505 1.4 35 3 15 0.5 0.7 17.2
    507 1.6 30 6 - - - -
    509 2.0 24 5 14 3 0.8 15.4
    See the N3ZI DDS-VFO 500-KHz prototype. Here is a link to the MFJ-269B modification to 500-KHz. The 600 meter Transmitter is a surplus NDB unit made by Soutern Avionics Co., model SS-800A, rated for 50w CW, 100w PEP. Testing with 0.1 Vrms drive from the DDS VFO produces a maximum output of 1.4 RF amps into 50-ohm termination (100w). My Bird-43 power meter reads 68w using a 100w HF element (100H). This element is derated by 3-dB at 500-KHz. Here is a block diagram and some photos: March 17, 2011: I modified a design by G3XBM to be a transmit converter from 10.461-10.478 MHz to 461-478 KHz. It uses the mini-circuits SBL-1 mixer to provide 10mw RF. A three-pole low-pass filter (W1VD) was used to filter out the 10-MHz products. LO is the station standard 10-MHz OCXO. March 3, 2010: An Elecraft K3/10 HF transceiver was ordered. The K3 will operate on 490-510-KHz at 0.1 mw by use of the General coverage filter unit and transceiver interface to bypass 160m high-pass fliter. This will enable running CW, QRSS, PSK, MSK, and WSPR modes on 600m band. The K3 will be able to drive the NDB transmitter as a linear amplifier up to 100w. Feb. 9, 2010: Building coil forms made from white plastic food carving board; Coil winder rig; coil wound; White plastic coil form; Coil transferred to form; coil installed at antenna mounted on a saw horse:
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