Current 630M Vertical Info

Well, it’s been awhile – relocated about 20 miles from the original station, and have not updated here for a long time – my bad.  I’ve had requests for details regarding the WG2XKA antenna system, so this is it.

RADIAL SYSTEM

The current system is located in my ‘front yard’ as this is the best spot.  Starting cold allowed me to plant a real radial system for 630m.  A 1′ diameter ring was constructed from #4  copper stranded power company wire.  The radials are soldered around this ring, then Kryloned.  Right now, there are about 80 radials of #18 solid soft copper wire, most in the 40′-60′ length range.  Many are over 100′ as space permitted.  The ring and radials are pinned right on grass that was cut short, using U shaped pins from a supplier, highly recommended, source noted later.  About 1000 pins were utilized.  Once the grass grows and after several summer cuts, they just disappear!  I should note that it’s important to locate several parallel radials directly under the top loading wire(s), extending past the top wires.

Below is the ring supported on firebrick, prior to adding radials.

HPIM1879

VERTICAL ANTENNA AND TOP LOADING

The vertical itself consists of #10 stranded, insulated wire, about 40′ in length.  Nothing fancy, the base consists of a cinderblock placed in the center of the above ring.  A board mounted vertically to the block supports the vertical via two dogbone insulators.  The base wire is directed to the tuning box about 1′ away.  Several 1″ wide copper straps from the base ring also enter the tuning box, which are also grounded by two, 4′ standard Radio Shack copper dipped steel ground rods.

The top loading consists of two, 100′ parallel wires of standard #14 hard drawn antenna wire – that stuff that wants to coil back up and kink! You know what we’re talking about here!  OK, originally I used a single strand, directly above the parallel radials described above.  It required ~350uH of base inductance in the form of a variometer to resonate the system at 475 kHz.  After seeing the cool pictures of old Marconi systems with parallel top loading, I decided to go that route.

Standard (in the north country), 4′ International Orange plow marker rods are used as the spreaders.  These fiberglass rods are about 3/8″ OD, and were drilled at each end to accept the top loading wires.  Let’s just say threading 200++’ of that nasty long term memory  antenna wire thru the spreaders and making everything parallel, singlehanded, batting Vermont bugs,  took several ugly hours.  The vertical itself joins the top wires at the 50′ center point via a cross wire.  The two parallel wires are also joined at the ends to form the top loading.

HPIM1879 HPIM2062IMG_0161

Above, the Marconi two wire top loading system.

The ends of the 100′ top system are insulated by two dogbone ceramic insulators on each end, supported by no stretch teflon rope shot over the appropriate trees by old friend Peter N1DYL (SK) RIP and his homebrew air cannon.  Rest in peace, my friend.  This line was first soaked in a harsh pepper (TOBASCO) solution to discourage chewing rodents.  So far, all good on that front.

The addition of the second parallel top wire resulted in a reduction of over 80uH in base inductance!!  Less R loss!!  This required building a new vario.

VARIOMETER AND MATCHING TO 50 OHMS

The vario is of standard design.  A two gallon Home Depot bucket forms the outer coil.  Knowing the inductance required, I designed it close to that value, with the inner coil designed to be close to my resonant point when positioned exactly halfway between min and max total vario inductance.  The vario is wound with #12 TFFN insulated house wire, supported as necessary with brass hardware.  A small, sweet ex-military?? shunt coil (about 40uH total) with 10 closely spaced taps allows matching the 50 ohm feedline to the system, using an alligator clip.  Depending on the weather and gods in general, upto 0.003uF of C is needed from coax center to ground to get a perfect flat match at resonance.  I use the outstanding RigExpert AA-30 analyzer to tune the system.   Variometer gory build details can be found in the Vario section.  Finally, the outer coil was liberally gooped with RTV to prevent coil movement.

IMG_0120HPIM1726

A motorized tuning system for the vario and remote capacitor switch box is under construction…details coming.

IN CONCLUSION

Like everything, this project is never ending and undergoing constant revision.  The antenna system, very short for 630m, has performed very well over two seasons and has met my expectations to date.

RADIAL Lawn Staples

…From ROSSRADIO.  Can’t go wrong, order the ‘Big Bag”!  Ross is a great guy to deal with.

http://www.rossradio.net/ground-radial-staple-pins-2/

CU guys on 630!

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