Friday, September 30, 2011

ARRL Homebrew 3 Challenge update: TR sequencing circuit

As soon as i installed my fast acting VSWR protection circuit i started tripping it when i was feeding my LPF & TR assembly.  There were moments where, the TR relay was not engaged but the PA was already biased and transmitting.  This would cause an instantaneous VSWR fault detected by the VSWR protection circuit, which would shut down the PA bias.

For this reason i had to add a delay which would turn on the bias to the PA after a short duration and which would keep the TR relay on for a while after the PA bias was shut off (see green board located below the PA itself).

It is certainly a challenge, TR switching a 100 watt + PA.