A HOMEBREW MULTIBAND SMALL SPACE ANTENNA

A HOMEBREW MULTIBAND HF COMBO VERTICAL/INVERTED - L SMALL SPACE ANTENNA10M-12M-15M-18M-40M-80M
MULTIPLE BANDS, 10M THRU 80M
SINGLE FEEDLINE
RADIO AMATEURS OF GREATER SYRACUSE
SETTLED ON VERTICAL VARIATIONS
REQUIRE SOME SORT OF MULTI-BAND APPROACH
RADIAL FIELD
2 BAND INVERTED L
PLAN IS TO FEED MULTIPLE VERTICALS AT ONE POINT JUST LIKE FEEDING THE COMMON FAN DIPOLE
20M 10/15 & 12/17
RADIAL FIELDS HAVE ALWAYS STOPPED ME FROM PLAYING WITH VERTICALS
BUT IT IS REALLY VERY SIMPLE, JUST TAKES TIME
WHAT I DID:
PURCHASED A RADIAL PLATE ON EBAY
BUILT A COAX FEED BOX USING 4”X4”X2” WATERPROOF JUNCTION BOX
DRILLED AN 18” DEEP HOLE WITH A 1-7/8” DIA. DIRT AUGER
CEMENTED A 3 FT, 1-1/4” SCHED 40 GALVANIZED PIPE, 18” DEEP – USE A LEVEL!
CLAMPED ON THE PLATE AND INSTALLED 25 X 20FT THHN WIRES CLIPPED TO THE GROUND WITH REBAR WIRE CLIPS
GROUND PLATE INSTALLATION
JUNCTION BOX
RADIAL PLATE WITH SOME OF THE RADIAL WIRES TEMPORARILY CLAMPED TO TOP OF GROUND PIPE
ANTENNA PLAN - SCHEMATIC
20M MAST 40M
1 0 M
/1 5 M
1 2 M
/1 7 M
80M
• 20M MAST IS AL CAMO MATL, BUT COULD BE PVC PIPE W/WIRE, OR FENCE TOP RAIL
• ELEMENTS ARE MOUNTED ON PVC STAND-OFFS FROM 20M ELEMENT
• ELEMENTS CAN BE THHN WIRE OR ANY CONDUCTIVE MATL.
• I USED 1/8” AL WELD ROD SECTIONS JOINED WITH CLIPS THAT I “SOLDER CAST” AND ENCASED IN HEAT SHRINK TUBING.
• BLOCKING COILS SHOWN ARE WOUND TO SPECIFIC µH VALUES
• MAXIMUM CURRENT IS AT THE BASE ….
HOW TO RESONATE 2 BANDS ON ONE ELEMENT
COILS CAN BE USED TWO WAYS ON AN ANTENNA ELEMENT
THEY CAN BE USED TO SHORTEN A SINGLE BAND ELEMENT. LOTS OF DETAIL ON THIS APPROACH CAN BE FOUND AT WWW.K7MEM.COM
OR…THEY CAN BE USED ON A TWO BAND ELEMENT TO ALLOW RESONANCE ON A HIGHER FREQUENCY BY BLOCKING RF AT THE RESONANT LENGTH. THE LOWER FREQUENCY IS NOT BLOCKED AND CAN THEN RESONATE USING THE FULL ELEMENT WITH AN EXTENSION (STINGER)
EXAMPLE
TO EFFECTIVELY BLOCK, WE NEED A REACTANCE OF >3500Ω.
PICK A DESIGN TARGET FREQUENCY
INDUCTIVE REACTANCE CALCULATORS CAN BE FOUND ONLINE: – ONE SUCH SITE IS:
HTTP://WWW.66PACIFIC.COM/CALCULATORS/IN DUCTIVE-REACTANCE-CALCULATOR.ASPX.
IN THIS CASE YOU ENTER THE DESIRED FREQUENCY AND A GUESSED INDUCTANCE AND YOU WILL GET A CALCULATED REACTANCE. I USED 7.150 MHZ AND 90 µH WHICH GIVES A REACTANCE OF 4048Ω.
THE MAIN ANTENNA SUPPORT WILL BE A MAST RESONANT ON 20 M AT 14.2 MHZ
THE 10/15M ELEMENT WILL TARGET 28.7 & 21.2 MHZ. THIS WILL REQUIRE A 19µH COIL
THE 12/17M ELEMENT WILL TARGET 24.93 & 18.11 MHZ. THIS WILL REQUIRE A 22µH COIL
THE 40/80 ELEMENT WILL TARGET 7.15 & 3.55 MHZ. THIS WILL REQUIRE A 90µH COIL
CALCULATING THE COIL TURNS FOR A GIVEN INDUCTANCE
I DECIDED TO USE 1” PVC AS A COIL FORM WHICH HAS AN OUTER DIAMETER OF 1.315”
I CHOSE 16AWG ENAMELED WIRE (.052” DIA.) FOR THE WINDING.
THERE ARE CALCULATORS WHICH WILL DEFINE HOW MANY TURNS ARE NEEDED FOR 90 µH OF INDUCTANCE.
http://www.66pacific.com/calculators/coil- inductance-calculator.aspx.
HERE YOU ENTER THE GUESSED TURNS, COIL DIAMETER AND WINDING LENGTH RELATED TO GUESSED TURNS (TURNS X DIA.), AND YOU WILL GET A CALCULATED INDUCTANCE.
40/80 METERS: 90µH TARGET
10/15 METERS: 19µH
12/17 METERS: 22µH
I FOUND THAT I NEEDED A FEW EXTRA TURNS
WOUND ON FORM & TESTED
COATED WITH LIQUID TAPE
20M MAST AND SUPPORT FOR OTHER ELEMENTS
INSULATED FROM GROUND BY ATTACHING TO A PVC PIPE WITH STAINLESS HOSE CLAMPS. PVC PIPE THEN DROPS OVER THE GALVANIZED GROUND PIPE.
OTHER ELEMENTS ARE SUPPORTED ON 12” PVC STANDOFFS, HOSE CLAMPED TO MAST
24” LENGTHS ARE CUT WITH 2’ DIA. HOLE SAW
NOTCHES ARE BAND SAWED FOR CLAMP BANDS
PVC SUPPORT
CONSTRUCTION VIEWS
20M MAST LASHED TO PVC PIPE INSULATIOR
AT RADIAL PLATE
ELEMENT SOLDER CAST JOINTS
INITIAL ELEMENT GUESSES ARE CALCULATED USING THE STANDARD DIPOLE CALCULATION:
L(ft) = 468/f (MHz) DIVIDED BY TWO
SO:
20M = 16.5 FT (USED 17.3 FT, HARD TO LENGTHEN MAST)
12M = 9.6FT (17M STINGER GUESSED AT 2FT)
10M = 8.20 FT (15M STINGER GUESSED AT 2FT)
ELEMENTS WERE CUT 1ST, COIL ADDED AND SUSPENDED OVER GROUND SYSTEM ON A FIBERGLASS POLE WITH A PULLEY.
BASE ELEMENTS WERE TUNED TO MINIMIZE SWR NEAR DESIRED RESONANT FREQUENCY
START WITH THE 20M MAST
FINAL TUNING APPROACH
FINAL TUNING IS AN ITERATIVE PROCESS DONE WITH FULL ANTENNA ASSEMBLED…THE ELEMENTS INTERACT!
FORTUNATELY THE ANTENNA IS LIGHT AND CAN BE LIFTED ON AND OFF THE GROUND SYSTEM EASILY.
TUNING THE STINGERS IS VERY TOUCHY AND A CHANGE IN STINGER LENGTH MAY AFFECT THE BASE ELEMENT. TRIM JUDICIOUSLY!!!
FINAL STINGER LENGTHS WERE:
1
1.5
2
2.5
3
20 METERS
SWR CURVES
1
1.5
2
2.5
3
10 METERS
SWR CURVES
1
1.5
2
2.5
3
15 METERS
SWR CURVES
1
1.5
2
2.5
3
0
0.5
1
1.5
2
2.5
NEXT WAS THE 40M/80M ELEMENT
SURPRISE! I COULD NOT GET A MEANINGFUL DIP LOWER THAN 5.5/1 ANYWHERE!!!
I LEARNED THAT ANTENNAS IN A YARD TALK TO EACH OTHER.
I HAVE A 40 M EFHW VERTICAL 25 FT AWAY, PERHAPS OVER A PORTION OF THE NEW RADIAL FIELD.
TURNS OUT, A YARD FULL OF ANTENNAS IS ONE BIG ANTENNA!
SO WE WENT TO A 30M/80M ELEMENT!!!
30M ELEMENT WAS CUT 23 FT TO INDUCTOR
SWR CURVES
1
1.5
2
2.5
3
30 METERS
SWR CURVES
0
0.5
1
1.5
2
2.5
3
3.5
80 METERS
I USED REVERSE BEACON NETWORK TO SEE HOW THE ANTENNA PROPOGATES ON EACH BAND
WWW.REVERSEBEACON.NET
SENT OUT 26 WPM CQ BLASTS FOR ABOUT 2 MINUTES
THEN CHECKED WHO HAS HEARD ME
PLOTTED RESULTS USING GRID SQUARES AND :
http://lcbsweden.com/www- sm7lcb/maps/qso_map/index.htm
THIS IS NOT AN NVIS ANTENNA
Europe
Europe
Europe
Europe
Europe
80M CW – 12N
30M CW – 3AM
30M CW 12N
20M CW – 12N
FINAL COMMENTS
THIS IS REALLY 4 SEPARATE ANTENNAS
BUILDING A RADIAL FIELD GIVES LOTS OF OPTIONS
2 BAND 40M/80M
2 BAND 15M/20M 22 FT VERTICAL + 6 FT HORIZONTAL
ANTENNAS CAN BE HUNG OFF THE SIDE OF TOWERS OR YOU CAN UTILIZE A TOWER FOR THE FIRST ELEMENT AND THEN RUN A WIRE OUT FROM THERE.
CAN UTILIZE WIRES WITH NON-CONDUCTIVE MASTS
…YOU GET THE IDEA
QUESTIONS?

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A HOMEBREW MULTIBAND SMALL SPACE ANTENNA