When the HF-GCS system is as active as it has been, it makes an interesting propagation indicator. Since they transmit on 4724 kHz USB, 6739 kHz USB (alternate 6MHz frequency: 6712 kHz USB), 8992 kHz USB, 11175 kHz USB (alternate 11MHz frequency: 11180 kHz USB), 13200 kHz USB and 15016 kHz USB...and since the transmissions are often simulcasted (and sometimes multicasted and simulcasted - that is, transmitted on multiple frequencies at once from multiple transmitter sites at once) you can often hear an echo on the "mid band" frequencies (usually 8992 USB and 11175 USB) due to multi-path propagation from several different transmitter sites.
On several instances I've heard different sites transmitting different messages on 11175, sometimes causing some pretty serious interference and QRM.
Next time you hear a lot of activity on 11175, take a look at (or a listen on, or both) 11180. It, along with other nearby frequencies, are often used for datalink transmissions around the same time voice traffic is taking place on 11180. You'll also find 11180 is often used for ALE sounding transmissions.
There are likely dozens of other frequencies that are part of the USAF HF-GCS system, including logged frequencies 6778 kHz USB, 6833 kHz USB, 6903 kHz USB, 6988 kHz USB and 7703 kHz USB. Additionally, the COTHEN HF system (used by DEA, ICE, DHS, etc), the FEMA HF nets (SECURE, SHARES) and the Civil Air Patrol/CAP HF-SSB nets have had USAF and other US military traffic on them. 6765 kHz USB and 6845 kHz USB (both SHARES frequencies) can sometimes yield some interesting monitoring.
7615 kHz USB is the CAP (Civil Air Patrol) nationwide net primary frequency. There are several 4MHz band regional net frequencies as well.
5211 kHz USB is FEMA-1 (FEMA HF night primary)
10493 kHz USB is FEMA-2
14597 kHz USB is FEMA-3 (FEMA HF day primary)
5236 kHz USB is SHARES night primary
14396.5 kHz USB is SHARES day primary
6910 kHz USB is SHARES Central
6765 kHz USB is SHARES North
6845 kHz USB is SHARES Northeast
7320 kHz USB is SHARES Southwest
It's a safe bet that most USAF, USCG, USN and USMC aircraft have the capability to communicate on the HF-GCS and COTHEN (Customs Over The Horizon Network) nets.
Topic: 11175 very busy (Read 4904 times)