EH-20 20m antenna By VE3RGW
Equivalent circuit of EH-20 antenna system. Upper cylinder Lower cylinder Phasing coil Common mode radiator Tune coil RF choke or 14MHz trap 50ohm coaxial cable 0-150pF (case dependent) To transceiver True ground (lightning ground and E ground)
Core section with cover removed. 3.5 Tin can 2 (2 ID) Set screw 2 space Set screw 2 space Phase line 2T Foam spacer 2 OD PVC pipe (15 total length) 3.5 Tin can (2 ID) Tune coil (14 AWG magnet wire) Resonance (Dip check) 16T(Tight wind) 0.5 space Ground ring RG-58U coaxial jumper 5 SO-230 socket
All climate cover 3 PVC cap 3 PVC pipe Hose cramp VSWR field optimization 3 to 4 PVC reducer
Preparing core form and bottom Prepare one 2 OD PVC pipe 15 long ing core form Off center by 0.3 Drill 0.2 hole here for coaxial exit Drill 1/16 holes from one end with following spacing: 2 0.5 1.5 0.3 5.25 1.25 0.75 Prepare two 2 ID 3.5 long tubes Drill one 1/16 hole near one edge Prepare a 2 PVC cover Drill one 0.5 hole at center Use SO-239 socket as mask, drill four 1/8 mounting holes.
Mount lower cylinder Slide the first cylinder onto the pipe, secure with one set screw. Push a 10 long 14 AWG magnet wire into the pipe, use open end to lead it out from the 3 rd hole. Clear out paint on either ends. Loop the ends closer to bottom of pipe to form the future ground ring. Secure upper tip to the lower cylinder.
Mount upper cylinder Push a 14 AWG magnet wire into the pipe from this hole, lead it out all the way from the other end. Insert foam spacer into the pipe and push it all the way down close to top of lower cylinder Work from opening, lead wire out from second hole, leave a 16 pig tail. Slide upper cylinder into the pipe. Wind the 16 pig tail as 2T on the pipe and secure the wire on the upper cylinder.
Prepare tune coil Tight wound 17T on the pipe and secure with a set screw, cut extra length to leave a 0.3 end with paint cleared for future work. Use a jumper to connect the ground ring to ground terminal of grid dip meter. Place sensing coil of grid dip meter close to tune coil. Identify largest dip frequency. Reduce number of turns of coil or extend length of coil to reach 14.0MHz. Fix condition of coil with heat shrink tubing or tape after reaching target. Re-verify coil s tune point after done and apply correction if applicable.
Connect RF port Prepare a piece of RG58U coaxial (8 long), open up and prepare both ends for further work. Solder one end to the SO-239 socket and mount the socket on the 2 PVC cover. Lead ends of RG-58U out from this hole, solder the shield to ground ring and secure core to tune coil at set screw (solder RG58U core to the exposed end of tune coil). If additional loading capacity is required, it can be soldered between set screw and ground ring.
Prepare climate cover Cut a section of 3 OD PVC pipe (20 long), press fit the top cover and the 4 reducer to both ends. Place a hose cramp on the 3 pipe for future work. Drill three 1/8 holes (120 degree apart from each other) 0.5 from edge of reducer
Install climate cover Put the core element into the climate cover with the base of the RF port level with the ends of the pipe section of the climate cover (using the 4 section of the reducer as base stand or as rain shelter to future cable connection). Cut out a ring of foam and slides it as a guard ring between core element and climate cover. Using previously drilled holes on the climate cover as mask, mark perpendicularly into the core and drill three 1/16 guide holes. Use 1 long set screw to secure the climate cover on the core element.
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). Re-position hose cramp for lowest VSWR at center frequency of operating band EH main body 18ft radial in free air connected to RF port 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.
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. Position hose cramp to obtain lowest VSWR at center frequency of operating band. 15-17 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
Finished view of RF port from lower opening of the antenna. Using a mesh or dish structure at bottom of the antenna to increase usable bandwidth. VSWR 1:3.0 VSWR with the antenna main body alone. VSWR with dish as ground plane. 1:1.5 1:1.2 14.0MHz 14.2MHz 14.4MHz 14.6MHz
EH-20 prototype 1 (on ground) and prototype 2 (on tripod mount)