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eHam Forums => Elmers => Topic started by: K7JQ on November 07, 2012, 02:06:54 PM



Title: Bias-T power injectors
Post by: K7JQ on November 07, 2012, 02:06:54 PM
Anyone have any experience using bias-T power injectors (such as MFJ-4116) to run 13.8V from a shack power supply through coax to power a screwdriver antenna motor, thereby eliminating a separate control line? Thanks for any input.

73,   Bob, K7JQ


Title: RE: Bias-T power injectors
Post by: W9GB on November 07, 2012, 02:17:49 PM
Bob -

Bias-Tee has been around a long time.
I first saw them in late 1970s for antenna mast mounted TV-FM pre-amplifiers for deep fringe TV reception.

Bias-Tee: Wikipedia
http://en.wikipedia.org/wiki/Bias_tee

Remote DC Power through your Coax Cable Phil Salas – AD5X (ad5x@arrl.net)
http://www.ad5x.com/images/Articles/RemoteDC%20RevA.pdf

You may find this article by K5LAD, of interest
http://www.hayseed.net/~jpk5lad/K5LAD%20Memories/Vols%2031-35/Memories--Vol33.htm

Example, PC Electronics (Ham TV)
http://www.hamtv.com/pdffiles/biasT.pdf

http://www.ece.vt.edu/swe/lwa/memo/lwa0135.pdf


Title: RE: Bias-T power injectors
Post by: K7JQ on November 08, 2012, 03:51:07 AM
Thanks for the info. I'll check into these sites.

73,   Bob, K7JQ


Title: RE: Bias-T power injectors
Post by: KG4RUL on November 08, 2012, 05:48:44 AM
It is possible to inject DC power into the coax in either polarity, thereby allowing up/down control of the screwdriver antenna motor and eliminating the separate control cable.  However, you lose the ability to count turns on the motor making it rather hard to return to a previous setting.  Also, depending on the antenna being used, running the motor to the stops repeatedly could cause damage.