Common-Mode Chokes
Whether called a hum eliminator, hum suppressor, humbucker, ground loop inhibitor, ground loop
isolator, or (mistakenly) transformer, the most widely used solution for hum bars is the common-
mode or CM choke. Although they use windings and core material like a transformer, their
construction and operation is fundamentally different

Referring to the schematic, note that the video signal current flows from device A to device B
through the upper winding and returns through the bottom winding. Because the two windings
have the same number of turns and the same current flows through them in opposite directions,
their magnetic fields cancel and there is no signal-related magnetic field. However, ground loop
current flows through the shield and inner conductors in the same direction (nearly all flows in the
shield since inner conductor circuit has much higher impedance). Therefore, ground loop current
does produce a magnetic field in the core that reacts with the coil to create an inductor (a.k.a.
choke), which determines common-mode impedance. The two “windings” are actually a single
length of miniature coaxial cable.

nductance for
commercial units generally ranges from 25 to
250 mH, adding 10 to 100 S respectively to the
impedance of the ground loop at 60 Hz. As
explained earlier, since the choke is now the
highest impedance in the ground loop, most of
the ground voltage difference will now appear
between its input and output ports.

However,
there is a limitation on the ground voltage
difference. The core material and number of turns
used will determine the common-mode voltage at
which the core will become magnetically
“saturated,” causing the impedance of the choke
to plummet. Therefore, ground voltage
differences over a certain level will cause hum
rejection to deteriorate or vanish.

Commercial units vary widely in this respect! Compare specs (if you can find them) carefully!

As with transformers, CM chokes are also passive and bi-directional. The major advantage of a
CM choke is wide bandwidth. Low-frequency response extends to dc and high-frequency
response is limited only by the length and type of coaxial cable used in the winding. Typical
bandwidths range from 100 to 1,000 MHz

Commercial units are available in 1, 3, and 5 channel configurations for composite,
RGB, RGBHV, and other multi-channel formats.

LEN LHDF03 HD-SDI Video Ground Isolator 4000 Volt – 4kV Breakdown
https://www.markertek.com/product/len-lhdf03/len-lhdf03-hd-sdi-video-ground-isolator-4000-volt-4kv-breakdown

3G HD SDI Galvanic Video Ground Path Isolator
Price: $209.00
https://www.shopfsi.com/L3GGI01-p/l3ggi01.htm

Technical Data sheet
tasker RGB 75 – 1×0,08 mm² Special Coaxial cable 75 Ω
https://www.tasker.it/db_files/products/fd9e5eaba9.pdf

Outer cable Diam. Ø 2,80