Adding A Tuner To 20 Meter Yagi.

By adding a tuner to the 20 meter antenna system it is now possible to operate on 15 meters, 17 meters, and 30 meters in addition to 20 meters.  The 20 meter yagi acts like a dipole on the new bands.  No gain or much directivity but a dipole at 60 feet is a big improvement over the verticals that have been in use.  The tuner is a LDG Electronics model RT-100 remote automatic tuner mounted in the shack. This is similiar to using the tuner in a transceiver except this has wider coverage.  A conjugate match can be made anywhere along a transmission line.  However, any time a tuner is located at other than the antenna feed point there is loss introduced in the form of coax loss due to swr and cable loss.  This is an experiment to see how well the concept will actually work in practice.

IMG_2138

Our installation consists of 160 feet of LMR 400 coax between the transmitter and the antenna feed point (100′ to the base of the tower and 60′ up the tower).  If the tuner was moved to the base of the tower 100 feet of coax would be bypassed.  For these calculations we use the KV5R.com web site.  At 17 meters for example, total loss at 160 feet is 2.8dB (coax loss plus swr loss).  For 25 watts out from the transmitter the antenna would receive 13 watts.  Moving the tuner to the base of the tower would improve the loss to 1.2dB. The antenna would receive 19 watts.  We ignored the loss in the  100 feet of coax from the transmitter to the tuner.  That loss would be .5dB (or 3 watts in this example) with virtually no swr loss.  Therefore the coax would deliver 22 watts to the input of the tuner and the antenna would receive  3 watts less..  With 1.2dB of loss the antenna was receiving 19 watts.  Now it would receive 16 watts.  In conclusion if we moved the tuner to the base of the tower the antenna would receive 3 watts more power  or .5 dB (16 watts vs 13 watts).  Is it worth moving the tuner to gain 3 watts (or .5 db)?

SWR Loss at 18.100 MHz

 100′       LMR400     =     3 watts

Update:  It seems to work on 17 meters.  FT8 contacts with Europe have been made.  For the next experiment it would be fun to try a better tuner, such as the MFJ 998RT, at the base of the tower.  This tuner would have less loss plus allowing bypass mode and tuning a wider range.  It is expensive and putting a up a second antenna might be less money.

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