Official 'ultralight' specs?


Good evening everyone -

Can anybody tell me what the 'official' specifications of an ultralight DX radio are?

The only consistent stat I can find is that it must not exceed 20 cubic inches. Other things I've seen online is that the radio must be a hobby grade receiver with no SSB capacity and also must not have or had a value in excess of 100$£€, when new on the market. 

Other than this I can't see too much. 

Thanks in advance. 

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