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Updated 2/3/18

This information is for reference only. The T-4 Line Isolators are no longer avaiable.

The Ground Loop Solution

The RFI Quick Fix™

Line Isolator Circuit

The T-4 and T-4G Line Isolator has been replaced by the T-4 Plus and T-4G Plus

T-4 Plus & T-4G Plus

The ULTIMATE - grounded version of T-4, provides even higher isolation.
VHF Line Isolators
T-6 & T-6G

Finally, a Line Isolator for 10, 6, and 2 meters! Check it out.

NEW!Low Profile, low power Line Isolator


Physically, only 1/4 the size of the T-4 Line Isolator, but but even better performance. It will handle up to 500 watts on SSB/CW.
* CW/SSB duty-cycles only. Not rated for AM, RTTY, or other high duty-cycle modes. Devices rated at 1500 watts or more will work at transceiver output levels on PSK-31 and similar modes without increasing IMD. The T-4-500 can be used on low duty cycle PSK-31 at the 100 watt level max.

The Ground Loop Solution

Multiple ground loops around various pieces of equipment can cause all sorts of problems. But, rather than getting deeper into a technical discussion, let's just try to avoid problems before they cause trouble. Solving the ground loop problem may be as simple as adding 'LINE ISOLATOR™ in series with the interconnecting coaxial cables between station equipment.

First, eliminate the heavy copper strap running along the back of the station equipment. Use the antenna tuner as a common ground point, 'Ground Central.' The heavy gauge wire, strap, or braid from your outdoor ground system will connect directly to the 'common ground point' on the back of the antenna tuner. Each piece of equipment will then be connected directly to this 'common ground point'. Actually, each piece of equipment is already connected, in a round about way, to the antenna tuner through the various pieces of coax that interconnect station equipment. Of course, it is this "round about way" that contributes to the ground loop problems. We can't eliminate the ground braid on the coax, but we can break up the external ground loops with LINE ISOLATOR.

Line Isolator™

The Line Isolator setup shown above works well for most stations. Customers report that LINE ISOLATORS™ inserted in series with the cables interconnecting the transceiver, linear and antenna tuner have eliminated stubborn RFI problems that resisted being solved by other means.

How it works

Placing a LINE ISOLATOR at the output of the transceiver or linear amplifier, prevents RF from traveling along the outer surface of the coax's shield. Any RF current flowing on the coax braid that can be radiated or coupled to other equipment is forced to ground by the very high impedance of the LINE ISOLATOR. RF current always takes the path of least resistance. Of course, the LINE ISOLATOR does not affect the signal inside the coaxial cable. The LINE ISOLATOR installed in series with the transceiver and linear amplifier helps the transceiver's output filters perform more effectively by breaking a secondary (leakage) path.

The T-4G

The T-4G is installed at ground level within a few inches of your ground system. It's built-in ground strap provides a direct path to ground for any stray on the coax, while the very high impedance of the Line Isolator's windings prevent from traveling up the coax an into the radio room. It's a very effective solution.

These Line Isolators are not always available. Call to confirm or check the web store.
The T-5G takes the process one step further. VHF isolation is added and a second ground strap is included for more effective bidirectional operation.

For more information -

Button More detailed graphic on the operation of Line Isolators
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You'll need a jumper cable to connect Line Isolators™ between equipment.

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