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Digital Point to Point on the 33cm Amateur Band

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The 33cm band offers unspecified bandwidth for unspecified digital transmissions using conventional modulation types as well as unspecified Spread Spectrum modulation although limited to 10W pep to the antenna.

In my reading of Part 97 the 33cm or 900MHz band is the lowest frequency band that does not have a 100KHz transmission bandwidth limitation. It also licenses the Spread Spectrum mode. These facts make it attractive for point-to-point communications requiring higher bandwidths.

  • The specific details are: § 97.301 33cm band.
  • Permitted signals: - MCW, phone, image, RTTY, data, SS, test, pulse
  • Specific limitations:
  • [7] A RTTY, data or multiplexed emission using a specified digital code listed in § 97.309(a) of this part or an unspecified digital code under the limitations listed in § 97.309(b) of this part may be transmitted.
  • [8] A RTTY or data emission having designators with A, B, C, D, E, F, G, H, J or R as the first symbol; 1, 2, 7, 9 or X as the second symbol; and D or W as the third symbol is also authorized.
  • [12] Emission F8E may be transmitted.

None of these limitations apply to Spread Spectrum transmissions which are covered separately as:

  • § 97.311 SS emission types.
  • SS emission transmissions by an amateur station are authorized only for communications between points within areas where the amateur service is regulated by the FCC and between an area where the amateur service is regulated by the FCC and an amateur station in another country that permits such communications. SS emission transmissions must not be used for the purpose of obscuring the meaning of any communication.
  • A station transmitting SS emissions must not cause harmful interference to stations employing other authorized emissions, and must accept all interference caused by stations employing other authorized emissions.
  • When deemed necessary by a Regional Director to assure compliance with this part, a station licensee must:
  • oCease SS emission transmissions.
  • oRestrict SS emission transmissions to the extent instructed; and
  • oMaintain a record, convertible to the original information (voice, text, image, etc.) of all spread spectrum communications transmitted.
  • § 97.313 (j) Transmitter power standards: No station may transmit with a transmitter output exceeding 10 W PEP when the station is transmitting a SS emission type.

The 33cm band is a shared band and used for portable phones, location services, industrial processes and more. In a point to point environment with good directional antennas reliable communications should be possible.

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Thursday, 29 September 2022