The 301 (take a look at it on the TenTec Sites) is a remote tuning knob.
It can be located anywhere on the desktop and allow armchair tuning of
your Omni V or VI.
It was discontinued some time ago by TenTec and there is a scramble to
locate any that are for sale.It is a rare item .
Many buy the parts seperatly and build their own .It was suggested
recently by myself and others that TenTec put the parts together and
sell it as a kit. ( the only part not available was the enclosure).
So its not antenna tuner.
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