LDG RT-100 Remote Tuner

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Part of our recent ARES NVIS testing over the past couple months was partly done in an attempt to find the optimal NVIS antenna system that is efficient, quick and easy to set up, does not require a lot of ancillary items, and uses a small footprint. A variety of dipole configurations and end fed wires have been tested. One of them we found to be intriguing was a non-resonant end fed wire using a remote tuner. By placing the tuner at the feed point, you pretty much eliminate all losses in the coax. The tuner is matching the wire AT THE FEED POINT, instead of taking into account losses from the coax being part of the antenna system. This eliminates the loss in the feedline.

While there is more testing to be done in the coming months, the one that got our attention was an antenna tested by NCARC club member Greg, N0EMP. This was a 41' horizontal wire connected to an Icom AH-4 remote tuner. The tuner was mounted on a fiberglass mast at 9', and the end of the wire was also terminated at a height of 9'. 

This was something I wanted in my antenna arsenal! But I wanted something that did not require a separate control wire like the AH-4 does. Enter the LDG RT-100. It uses bias tee to send DC power over the coax to start the tuning cycle. The unit runs $270, and comes with the RC-100 bias tee control unit.

I recently tested the unit out in the Pawnee Grassland, my favorite POTA place. The purpose of testing on this day wasn't necessarily to test it's NVIS capabilities, but more so to find ways to mount the unit, wire length, sending DC power to the unit, etc. 

Test conditions were:

          - Yasesu FT-857D

          - 84' radiating element, 24ga SOTABeams wire

          - No counterpoise

          - PL-259 with a 12" wire installed, plus a female bullet connector

          - 24' fiberglass military mast

          - DIY drive-on base used to mount the RT-100 at 3' AGL

          - Cold

          - Windy

Before leaving home, I soldered a 12" piece of 18ga wire to a PL-259 connector, then added a female bullet connector to it. I also added a small stainless steel threaded eyelet to the mounting surface of the unit, and clipped in a small carabiner. This was, I can easily change out the length of wire by plugging in a new wire to the pigtail, then securing it to the eyelet with a plastic SOTABeams strain relief.

The tuning cycle can actually be initiated in a couple of ways. I first used the RC-100 remote control unit to send the tune signal to the RT-100. However, the unit will actually start tuning itself if a high SWR is detected, so simply placing the radio in AM mode and keying the mic will initiate a tune. But then I remembered something..... I have a Yaesu, and it has an ATAS tune function built in! The ATAS works by sending a certain DC voltage value down the coax to tune the antenna UP, and a different voltage to tune the antenna DOWN. Hmm, maybe I can enable the ATAS function and initiate the tune from the radio without changing bands or power settings?

Why YES, I can! I went to menu #085 (TUNER/ATAS) and set it to HF. Then pressed the FUNC key and turned the multifunction knob until TUNE appeared on the lower left of the display. Pressed it once to turn on the ATAS tuning in the radio. Then, to initiate a tune, I pressed and held the TUNE button to send DC power down the coax. Once the tune cycle started, I let go of the button. When a good match was found, the radio automatically shut off the tune function. 

This revelation made the process so much easier, and solved a couple of the above mentioned testing requirements. Next time out, I will use the FT-891, and enable the ATAS function in it as well.

The antenna performed quite well. So much so, that I am now rethinking the 40m EFHW I use at home. I could replace the 49:1 transformer with the RT-100, and change out the ~66' wire with a 71' or 84' wire.