This is from the CAA Information Circular AIC 73/2003 24 July 2003
Date: 11 - 22 August Inclusive Times Between 0900 and 1630 local for full period and between 0100 and 0300 local on 17 & 20 August.
For the period 11 to 22 August inclusive jamming to a maximum range of 19nm and between 0100 and 0300 local 17 and 20 August to a mixmum range of 33nm.
The land based jammers will be within 3nm of N520130 and W0033730 within the MoD Sennybridge Training Area Powys Wales.
The trials should not cause interference to other land based or airborne navigation or communication equipment.