Broadcast Concepts Inc
11700 NW 102
nd
Road Suite 4Medley FL 33178
Tel: 305.887.8400 FAX 305.887.8444
Broadcast Concepts Inc
Revised 8/20/2014
6
Low Pass Filter
A low pass filter is required to reduce harmonics. Harmonics from FM transmitters are regulated by most
government regulatory authorities. Any of our low pass filters rated for at least 1000 watts can be used with this
pallet. It is critical to install a 6.0 (or longer) inch piece of RG400 between the pallet output and the filter input to
prevent a filter reaction. When a filter reaction occurs the pallet sees a high mismatch which can cause the transistor
to overheat and slowly burnout. The cause of filter reactions is not fully understood; however, reflected harmonic
energy at a certain phase and frequency is strongly suspected. Filter reactions do not occur when 2 or more
amplifiers are power combined since the combiners provide isolation from the low pass filter.
The BLF188XR can operate into open and short circuits without damage; however, operation into a mismatched
load for even a few minutes can cause the transistor to fail from thermal stress. The BLF188XR is not clown proof.
Thermal overload and RF overdrive will still destroy the transistor. It should be noted that load mismatches that
cause the transistor to draw high current are the ones that are most likely to cause a thermal failure
.