Proposed 60m amateur band power limit

The WIA announced on 19/11/2015:

The World Radiocommunication Conference (WRC-15) in Geneva has agreed on a secondary allocation of 5351.5-5366.5 kHz for the Amateur Service, with regional power limits of 15 watts to 25 Watts measured in effective isotropic radiated power (EIRP).

This prospect has lots of hams excited, and some wringing their hands over the power limit expressed in the release.

Compliance with this power limit (1W EIRP in this region) may well challenge most modern hams (though EIRP power limits are not new to the Amateur LCD) and perhaps if that is to be the limit, a set of simple compliance guidelines be endorsed by ACMA to assist compliance.

Rationale

Stations operating on the 60m band will fall broadly into two groups:

  • mobile stations that use short inefficient antenna systems; and
  • fixed stations that may use efficient antenna systems with considerable improvement from ground reflection.

Mobile

Practical mobile antennas for the 60m band are likely to be short monopoles in some form and are unlikely to have an efficiency above 20%. Combined with the Directivity of a lossless short monopole being 3.0, gain is 20/100*3.0=0.6 (-2.2dBi). Since TxPower=EIRP/Gain, maximum transmitter output power under these assumptions would be 15/0.6=25W.

Fixed

Practical fixed antennas for the 60m band include ordinary wire dipoles of various lengths, and possibly some more directional arrays, and are unlikely to have Gain (including ground effects) greater than 10 (10dBi). Since TxPower=EIRP/Gain, maximum transmitter output power under these assumptions would be 15/10=1.5W.

A possible simple approach

  1. The power limit for 60m band is 15WpX EIRP.
  2. Compliance may be demonstrated by valid field strength measurement, or by valid modelling or by any other method acceptable to an ACMA inspector.
  3. Alternatively:
    1. mobile stations (meaning a station that is capable of travel on public roads) with transmitter output power no more than 25WpX will be taken to be compliant; and
    2. all other stations with transmitter output power no more than 1.5WpX will be taken to be compliant