EH-20 20m antenna. By VE3RGW

Transcription

1 EH-20 20m antenna By VE3RGW

2 Equivalent circuit of EH-20 (prototype 2A) antenna system. Upper cylinder Lower cylinder Ground Counter pose Phasing coil Impedance transformer and tune circuit Tune coil Feed coil To transceiver RF choke or ferrite bead 50ohm coaxial cable Common mode radiator True ground (lightning ground and E ground)

3 Upper section with cover removed. 6 Brass tube (1.4 inner Dia) Phase line 1T (15cm wire length) Foam spacer 1.5 space 1.25 PVC pipe (30 total length) 6 Brass tube (1.4 inner dia) 1.5 space Tune coil (14 AWG magnet wire) Resonance (Dip check) 22.5T-14MHz (Tight wind) Feed Coil (1T 0.3 from tune coil) Coaxial radiation suppressor 5T coaxial choke (Do not use ferrite beads)

4 Lower section Tune coil Feed coil Common ground point Coaxial choke 1.25 PVC pipe 10 long 1.5 fencing pole The lowest cylinder is for mounting, weather protection of connector and grounding. It is joined with the common ground screw with a jumper inside the PVC pipe. SO-239 UHF socket (see later document regarding ways to secure the socket.

5 Preparation for the core form and cylinders Drill holes on a 30 long 1.25 OD PVC pipe Front side /2 dia.hole 1/8 dia.holes Back side Upper / lower cylinder 1.25 x6 brass pipe

6 Mounting upper / lower cylinders Wind electric tape to fit up dia. with brass pipe Slide lower cylinder into position and secure with set screw Slide upper cylinder into position and secure with set screw

7 Preparation of coaxial feed hole Set screws for upper / lower cylinders 4.5 drill two ¼ dia holes to pass RG-58U coaxial Preparation of RF feed ports File 4 slots as a seat for the UHF socket Drill 4 1/8 holes on pipe edge above 4 corners of SO239 SO-239 socket Bottom of pipe

8 Connecting lower cylinder Push 14AWG magnet wire into the pipe Work through the 0.5 hole, bring magnet wire out from the 1/8 hole above lower cylinder Clear out laminating paint and tight up to cylinder via set screw Leave 2 tail, bend it around the pipe to the opposite side of the pipe for future work.

9 Connecting upper cylinder Push 14AWG magnet wire into the pipe Work through the 0.5 hole, lead magnet wire out from 1/8 hole below upper cylinder, make it as a 15cm long pigtail. Remove laminating paint for the last 2cm of this pigtail. Wind this magnet wire on the pipe as the phasing line and secure it to the upper cylinder via set screw. Smooth out 300cm of magnet wire for tune coil.

10 Building of tune coil Tight wind the magnet wire on the pipe as about 25T and temporary secure it with a set screw on the lowest hole (here on after termed as ground set screw). Remove paints at the ends of magnet wires from both cylinders. If proper antenna analyzer is available, connect RF input port to the upper cylinder via tune coil and to lower cylinder s pig tail. Identify the frequency where Z= 0 or close to 0. If grid dip meter is to be used, loop the two wires and place sensing coil of the grid dip meter next to the tune coil, scan via available oscillating frequency until the dip point (resonance status) is identified.. Reduce number of turns or stretch length of coil to raise resonance frequency. Work out a winding that yields maximum dip (or resonance) at 14.10MHz.

11 Building of feed coil After tune coil s turns and length is determined, clean up 20cm of paint from the magnet wire (area passing the set screw) and cut away the rest leaving a 15cm pigtail for making the feed coil. Push 40cm of RG-58U coaxial into the pipe from one side hole next to the ground set screw. Remove about 15mm of the plastic jacket. Separate the blade from core and clean out 3mm of PVC insulating material to expose the core conductor. Pull the cable back until only the blade and PVC core is exposed. Wind the 15mm pigtail on the pipe (1T) right on top of tune coil (with insulation). This is key to obtain lowest VSWR or power coupling. Remove laminating paint from tip and solder it to the core connector of RG-58U. Solder the blade section of RG58U and pigtail from lower cylinder to magnet wire underneath ground set screw.

12 Connecting to RF port Cut extra length of the coaxial cable, leaving a section of about 25mm exposed from bottom of pipe. Clear out 20mm of Plastic jacket and 5mm of PVC insulation material to expose core conductor. Solder the core conductor and blade to the SO239 socket.

13 Grounding spot and climate cover Wrap up the end of the pipe with metallic sheet metal or tight fit aluminum pipe. Use 4 tie wraps to lock up the SO239 on the pipe after properly seating. Connect a short jumper between the common ground connect point to the metal pipe right under it. Metal ground has to be provided during final tune up. Acceptable ground included metal pipe inserted into wet soil, metal tripod or mast over 8ft length. Or a piece of wire cut to quarter wavelength of the operating frequency is also acceptable. Prepare a piece of 2 PVC vacuum pipe with a tight fit cap as weather protection cover. Resonance frequency will drop after cover is applied. The hose cramp on the climate cover is for final VSWR adjustment to compensate for different mounting environment (the closer the cramp to the coil, the higher the frequency). Readjust tightness (or turns) of the tune coil with cover installed ensure reaching the lowest VSWR reading at operating frequency. Seal the coil section with tape or heat shrinking tube and recheck overall VSWR (or resonant point).

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15 Tune coil parameter (12MHz-29MHz) cylinder capacitance=15pf at 17MHz, P2A for regular grounding, P2B for no-ground mount profile Band M5 20m Turns 30T 28T 26T 22.5T (P2A) 24.5T (P2B)) Coil length TBA TBA TBA Tight Tight Bandwidth TBA TBA TBA +/-150KHz +/- 280KHz Resonance 12.2MHz 12.8MHz 13.2Mhz 14.1MHz 14.2MHz Band M6 M7 15m Turns 15.5T 14.5T 12T 12.5T 11T Coil length Tight Tight Tight Tight Tight Bandwidth Resonance 17.0MHz 18.5MHz 19.7Mhz 20.5MHz 21.0MHz Band M8 11m 10m-A 10m-B Turns 10.5T 10T 9T 9T 9T Coil length Tight Tight 1.0 long 1.3 long 1.5 long Bandwidth +/- 0.15MHz +/- 0.5MHz +/- 0.5MHz +/- 0.5MHz Resonance 21.5MHz 22MHz 26.5Mhz 28MHz 29.0MHz

16 Equivalent circuit of EH-20 (prototype 2B) antenna system. Used for application without true ground (feed line radiation assisted) Upper cylinder Lower cylinder Phasing coil Tune coil (2 more turns required to compensate poorer ground) 24.5T instead of 22.5T as in 20M-P2A Ground ring Common mode radiator To transceiver True ground (lightning ground and E ground) RF choke or ferrite bead 50ohm coaxial cable

17 Upper section with cover removed. 6 Brass tube (1.4 inner Dia) Phase line 1T (15cm wire length) Foam spacer 1.5 space 1.25 PVC pipe (30 total length) 6 Brass tube (1.4 inner dia) 1.5 space Tune coil (14 AWG magnet wire) Resonance (Dip check) 24.5T-14MHz (Tight wind) Feed Coil (1T 0.3 from tune coil) Coaxial radiation suppressor 5T coaxial choke (Do not use ferrite beads)

18 Lower section To lower cylinder Tune coil Common ground point Coaxial choke 1.25 PVC pipe SO-239 UHF socket (see later document regarding ways to secure the socket.

19 Regular mounting profile (controlled hot spot) The antenna body is mounted on mast or tower with at least 15ft clearance from ground level. The mast is of metal and should be grounded (or be inserted into soil for at least 2 ft). Ground plane or additional ground mesh close to bottom of main body of antenna is recommended (but not essential). EH main body 18ft radial in free air RF choke 8 loop with 8 diameter Transceiver 50ohm cable of any length RF choke (safety precaution, not essential) 8 loop with 8 diameter Grounded mast or ground plane installed.

20 Using coaxial feed-line as common mode radiator (un-controlled hot spot) This profile is used when well grounded metal hold points is not available. For example, when the antenna is mounted on chimneys, roof tripod, wall mount without ground, tripod on balcony. Since part of the feed line will radiate, coaxial radiation will be a concern if magnetic interference is caused to nearby appliance. Feed line cable should be secured with clearance from nearby metal or grounded material. Use hose cramp on external climate cover to control frequency for best VSWR occurrence RG-58U cable Hanging in free air EH main body Cable junction (exposing shield layer for ground connection) 50ohm cable of any length Transceiver RF choke RF choke (essential) (non-essential) All chokes 8 loop with 8 diameter Tripod or roof mast (not grounded, 5-15ft) Ground strip into top soil Or water pipe ground outside house

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