[Elecraft] RF Feedback

[Stuart Rohre]

I have seen various appearances of RF feedback in SSB radios.  Some of the
causes I found were:   Use of a coiled cord mike cable with a coiled cord
paddle/bug cable, and the shields formed inductors, since there was RF on
ground.

Magnetically coupled RF, because the SSB rig was set on top or too close to
the side of a transmatch with large tank coil.

The RF makes its way to the audio circuits and can be easily rectified in
input preamps of the audio chain.  Then it latches up the ALC, and the ALC
indicator will be excessively high, or on all the time, if an ALC light.

Try beads and pf value caps to decouple the RF, if it is on hot mike leads.
You may need a bead over the outer shield, if the inductor effect is a
causative path for RF entry to rig.

Is the RF amp in steel case or aluminum box?  Aluminum does not provide
adequate magnetic shielding.  Spacing the amplifier away from other rig may
help.  Bypass everything in and out of amplifier, filaments, B plus, use
shielded B plus cables, etc.

Make sure no coax jumpers approach a quarter wave at the band in use.
Gl and 73,
Stuart K5KVH