Transmitting on 2200 meters or 138.000 KHz using WSPR Digital mode. Set receiver to 136.500 KHz USB.
Antenna-Voice of America.
I started my 475 KHz experiment by modifying a 160 meter four wire vertical cage remote tuner. The four foot square cage antenna is supported three feet off the east side of the tower at 95 feet. Located 15 feet above the cage is a 12-foot diameter aluminum tube capacitance hat. Two 12 X 6 inch diameter 300 uH coils were used for the matching inductance. Both coils are in series and mounted on top of the remote tuner enclosure. Coax is fed from the shack with its shield bonded to the 200 plus radials, along with several ground rods used for tower lighting protection. The remote tuner was modified with additional Sangamo mica transmitting capacitors and one roller inductor that was used as an adjustable shunt for 50 ohm impedance matching. The four wire vertical was only used for a short period of time as coupling to the tower during high winds created a high SWR.
The testing of 475 KHz continues with a 220' (non-resonant) dipole fed with 300 ohm ladder line. The non-resonant dipole is attached to the tower by use of a 10 foot section of 1.5 inch solid fiberglass rod. By tying both of the ladder line conductors together it is now configured as a Marconi 'T', with the other half of the antenna being the radials and ground rods. Both of the original 300 uH coils were used for loading. With the use of the dipole, the SWR is considerably more stable than with the vertical cage. The Aim-4300 antenna analyzer is used to collect all antenna data recorded. Array Solutions carries the entire line of Aim products.
Resonating 137 KHz or 2200 meters was a rewarding challenge. The 300 ohm ladder line feeding the Marconi 'T' antenna is still in place. The two coils to the right are actually four coils that are in series, borrowed from a previous antenna experiment. The dipole coils worked great for the initial testing as being able to connect them in various combinations made the task of tuning 137 KHz a lot easier ! Each long (dual) coil is 1.24 mH, yielding an inductance of 2.48 mH while adding the 6 x 12 inch 300uH coil produces a total inductance of 2.78 mH.
Moving to 137 KHz required more inductance than that needed on 475 KHz ... 2.526 mH in total. This move involved winding a 12 x 36 inch Acrylic tube with # 10 gage solid bare copper wire that was spaced at 6 TPI. Red weed-cutting line (.100") was used for coil wire spacing, giving the coil an interesting red appearance! The coil was then installed on a Rubbermaid trashcan that was turned upside down ... luckily it was a perfect fit. Elevating the coil helped to reduce ground coupling and signal loss. The original 300 ohm ladder line was removed and replaced with #10 tin plated solid copper wire.
Five coils in series for 75.5 KHz ! Coil enclosure now has side panels as seen in our Photo Gallery.
The 475 KHz "Loaded Dipole Project" coils really came in handy for LF testing. Both are held in mid-air using a 1 inch thick piece of polycarbonate material. The total inductance is now 7.2 mH!
The remote tuner uses 60nF for tuning. The white mounting material used for mounting capacitors and other components is 1 inch thick UHMW polyethylene. This helps to stop high voltage arcing to the steel back panel in the enclosure. I hope you enjoy the Photo Gallery. I have so many photos to load it will take months to complete! At the top of the page, the 2015 - 2017
137 KHz WSPR maps are being loaded as time allows. Thanks for stopping by. Ron NI7J-WH2XND
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