Ionospheric HF radar spectral regulations

This page is focused exclusively on United States of America Amateur Radio regulations.

Beacons in the Amateur Radio Service: for HF (sub-50 MHz) frequencies, 10-20 kHz bandwidth might be legally possible on these frequencies with up to 100 Watts conducted transmit power for one-way transmission under the Amateur Radio Service, § 97.305(c).

frequency range [MHz] notional wavelength [m]
1.8 - 2.0 160
3.6 - 4.0 75
7.125 - 7.30 40
14.15 - 14.35 20
18.110 - 18.168 17
21.20 - 21.45 15
24.93 - 24.99 12
28.3 - 29.7 10
50.1 - 54.0 6
144.1 - 148 2
222 - 225 1.35
902 - 928 0.33
420 - 450 0.70
1240 - 1300 0.23
2300-2310, 2390-2450 0.13

Along with numerous higher frequency bands.

Note: 7.075 - 7.10 MHz is NOT phone/image in the lower 48 states of USA

Beacons may be locally or remotely controlled. An easy method of legal remote beacon control may be accomplished via a simple website. The control operator sees the status of the beacons and can click a button to turn individual beacons on/off from their smartphone without need for an app. One control operator can control an unlimited number of stations remotely.

Legal Beacons under FCC Part 97 (Amateur Radio Service):

  • § 97.203(g) beacon may transmit one-way communications
  • § 97.203(c) beacon can transmit up to 100 Watts conducted power
  • § 97.203(b) beacons may transmit on multiple amateur bands simultaneously, one “channel” per amateur band.

Examples of practical usage of beacons under § 97.203 include worldwide networks of beacons using a variety of emission modes exist throughout every amateur HF band. The NCDXF network transmits 24/7/365 with 100 watts on several HF bands with stations worldwide since 1979.

Instantaneous bandwidth under FCC Part 97

§ 97.307(f)(2) No non-phone emission shall exceed the bandwidth of a communications quality phone emission of the same modulation type. DSB-AM voice transmissions may perhaps occupy up to 20 kHz instantaneous bandwidth or so, although 10 kHz bandwidth is perhaps more common. Perhaps we are transmitting an “image” or a digital “voice” transmission, in a manner that is convenient for ionospheric sensing with an HF radar beacon network.

Some people incorrectly latch onto § 97.203(d) which applies to automatic control beacons only. That is, beacons that no human needs to actively monitor or control. In contrast, we propose radar beacons that are remotely controllable over the internet via any web browser as has been well established.

Non-Beacon strategies relevant to VHF+ operations include:

  • Automatic control: No control operator, local or remote: § 97.113(d) Includes auxiliary, repeater, and space stations.
  • Test (> 51 MHz) Emissions containing no information: § 97.305(b) Test does not include pulse emissions with no information or modulation unless pulse emissions are also authorized in the frequency band. 1500 watts PEP conducted power limit, appears to be no bandwidth restriction.
  • Spread spectrum: § 97.313(j) Spread Spectrum (>222 MHz) May fill entire amateur band, 10 watts PEP transmit conducted power.