[Premium-Rx] Racal Sync Detector

[Carcia, Francis A HS]

Hi All,
The Racal sync detector is hard to align correctly but I have found a easy
way to get the best performance. All my RA6830 modules came with the tuning
slug for the MC1357 inductor sticking out of the case. This made me curious
as no good design would leave it in that position. The MC1357 is the carrier
recovery for the sync detector and FM demodulator. The FM demodulator works
over a very wide range so the adjustment isn't critical.
I found the best way to adjust this inductor is in AM mode with a CW
carrier. The carrier was injected into the module at 455 KHz. I kept
reducing the level while tuning the slug for best carrier recovery into the
MC1496. When I was done the slug
was inside the core where it belonged. Also there was almost no audio if the
FM mode was selected while listening to a AM signal. This same circuit is
used in the RA6790 but I don't know the best place to inject the carrier. I
suppose it could come from the antenna input at any frequency then reduce
the level with the manual gain control.  fc