Use the list below to quickly tune to the most used US Air Force High Frequency Global Communications System (HFGCS) frequencis as received directly by internet software defined radio (SDR) sites. Simply find the location you want and click on the frequency to open a receiver in a new browser tab. The best receiver locations appear to be near Cape Cod, Massachusetts and the Pacific Northwest (Idaho, Montana, Utah). Sites below are selected by receiver performance and proximity to HFGCS transmitters. Frequencies 4724, 6739, 8992, and 11175 are the primary and secondary ones used for EAM and SKYKING broadcasts, though there are times when the E6 TACAMO or E4 NAOC aircraft can be heard elsewhere. If there is a training exercise or real-world battle, hunt around other frequencies, such as 6697, 8776, or 11244.
Some sites have taken to blocking frequencies with the "mask" function. If the SDR goes silent on 11175, for example, try another HFGCS frequency or use a different SDR site. If you are geo blocked from any SDR site, evade the blockage by deleting your browser cookies and using a VPN or SSH tunnel to connect from a different country. If you want some excellent links for popular AM / Mediumwave stations, see the KiwiSDR Canada, KiwiSDR Australia and New Zealand, and Mediumwave WebSDR lists.
Since propagation conditions vary between different receiver sites and frequencies, try different combinations to find which ones work best for your desired stations. Most KiwiSDRs have rather high default gain settings, producing plenty of noise, which can be bothersome. To avoid listener fatigue, reduce the AGC threshold to a setting of about 80 dB. The KiwiSDR standard USB filter bandpass is good for HFGCS traffic; setting the top limit to 3.5 kHz is a match for the broader bandpasses on the network. Stations on the net operate with precise, dead-on tuning: less than 5 Hz above or below the published frequencies.
Please be a fair listener on these radio servers. Avoid excessive time or opening multiple SDR tabs from the same site at once, as site operators detect and block users or frequencies who draw excessive bandwidth.
If you find interesting action on the HFGCS frequencies, give some thought to making an audio recording or screen capture video to share on sites such as YouTube or Soundcloud