[BC] Humming Preamps

[Mark Humphrey]

On 4/7/07, RadioPower Webmaster <webmaster at radiopower.org> wrote:
>
> yes, we have the misfortune to be located 1/2 mile from the local FOX
> TV and Radio studios with multiple transmitter towers in line of
> sight view.

Have you tried attaching ferrite beads to the cables at the input to
each preamp?  You might initially try snap-on cores, which are easy to
install) and see if they make a difference.  If you can run multiple
turns of cable through each bead, they will be more effective.  Mix 43
ferrite covers a fairly wide frequency range, although Mix 64 is
better at VHF and UHF frequencies.  More info:

http://www.antennex.com/shack/Dec99/beads.htm

I once worked at an FM station on the 17th floor of an office building
in downtown Rochester, NY, less than a mile from the Pinnacle Hill
antenna farm, home to three 316 kW high-band VHF and two 1 MW U's,
transmitting from relatively short towers.   Our studios had a
beautiful view of those towers, so we had trouble with sync buzz under
the audio until it was cleaned up by adding shielding (for instance,
aluminum screens behind the windows), ferrite beads, low-inductance
ground straps, etc.   Most stock audio equipment required modification
to get the noise down to acceptable levels; our biggest challenge was
a Tascam Model 15 console with unbalanced ins and outs.  Before adding
RF filtering to that, we could connect its line output to a scope,
open the input faders and clearly see the sync pulses.

Mark