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I was a RF design engineer in my past life and have been designing solid state amps for over 35 years. Prior to founding my own company, my employers were TRW Semiconductors, Motorola, HP and Eimac. My current home brew project is a 16 transistor linear HF amplifier that will provide 1500 watts output in my car.

(Electric scooter photo - I am running an ICOM 706 at 100W with a Hustler antenna on 40M)

HOMEBREW MOBILE HF ANTENNA

I built my HF 40-10M mobile antenna using 7 feet of 3/4 thinwall (EMT) electrical conduit as the base with 3/8 - 24 thread nut and bolt welded on opposite ends, a 6 inch dia., 6 inches high loading coil of #10 wire with turn spacing of about 1/4 inch, supported with four plastic vertical support/coil turn spacers that were cut from plastic clothes hangers, marked, notched with a soldering iron and then placed inside the coil. The outside of the coil was "hot" glued to the inside plastic supports using remnants from the clothes hanger as the glue and my soldering iron to melt it so the coil would hold it's shape. (I used white hangers). To take the "wrinkles" out of the #10 solid electrical wire, I first strip the insulation from about 10 feet, then place one end of the wire in a vice and the other end in my electric drill and spin the wire while pulling on the drill away from the vice to stretch the wire. The wire is then "work hardened" and will be surprisingly straight The loading coil has a 1 inch diameter, 6 inch long fiberglass rod in the center and the rod has 3/8 -24 nuts epoxied into each end with a 5 foot ss whip at the top. This 12 1/2 foot tall antenna mounts on a 2" wide L channel iron that is welded to my Ford Winstar van's frame and trailer hitch about 8 inches behind the drivers side rear wheel, and extends about 6 inches out from the drivers side of the van's body. At 2 inches from the end, I have a hole drilled in the channel iron and have bolted an insulated Hustler Quick disconnect adapter. The L channel is lined with thin copper sheet connecting the antenna base ground/matching coil to the van body, chassis, trailer hitch, A/C lines exhaust, etc. with additional copper strap and braid. I run 1/4 wave counter poise insulated wires from the antenna base ground forward towards the engine between the frame and body for 10, 15 and 17 meters. A 10 inch jumper of stranded wire is soldered at the bottom of the loading coil and clips to the coil. I move the clip to the appropriate turn that resonates the antenna for a particular ham band. Because of the power level I am running, I made a very strong clip from stainless steel.

SHUNT COIL

The antenna's base impedance is matched with a 1.5 inch dia #12 AWG with 10 turns. I striped the insulation off of some old #12 Romex house wiring that I had lying around. Placed one end in a vice and the other end in my electric drill and twist it while pulling the drill away from the vice slightly to "work harden" the copper wire. It makes it slightly stiffer and springy while taking the wrinkles out of the wire. You will be able to see some spiral marks on the copper as you twist for about 10 seconds (depending on length). I wind that springy wire on a 1" ID PVC pipe as tight/close turns as I can. When I reach 10 turns, I let go and the wire turns will spring to a slightly larger diameter, about 1.5" and be spaced about one wire thickness apart. I solder a lug on each end for attaching it to the antenna base and ground and then spray the finished coil with clear lacquer so it retains the shiny copper look. The exact number of turns may vary with your installation to achieve the best match. Once done, you just forget it and enjoy your antenna. I do not know of any commercial matching units that will handle high power. If you plan on running power, you should consider using a shunt coil. I use one with 1000 watts output. It is easy, cheap and works.

SECONDARY HF MOBILE ANTENNA

My secondary and much more attractive mobile antenna is a HI-Q 5-160RT, with a shunt coil from the antenna base to ground for matching. I find myself using it more recently because of the motor driven coil which allows me to change bands without stopping the vehicle.

HOMEBREW AMPLIFIER It uses (8) 2SC2879 transistors and provides about 1KW PEP out. New amplifier on the drawing board.

VEHICLE - Additions to allow use of 1KW amplifier

Every spark plug wire and the entire ignition system is shielded, plus has "clamp on ferrite" on the low voltage ignition leads. Both air conditioning 12V fan motors are filtered with bypass capacitors. Ferrite is clamped on most auto microprocessor leads and there are about 15 ferrite beads on the RG 214 coax running from the linear amplifier near the antenna. The ferrite on the coax acts as a W2DU 1:1 current balun. All leads to or from my ICOM 706mkll transceiver have clamp-on ferrite which prevents RF from interfering with my modulation which would result in distorted transmit audio. Prior to installing "lots" of ferrite, the car engine would stall when I transmitted. It is embarrassing to lose power at freeway speeds.

I LOVE DSP. The ICOM 706 DSP is nearly worthless, so I do not use it. I installed an AmCom DSP speaker which has been modified to conveniently allow switching the speaker from DSP to non-DSP mode. The DSP speaker removes power line, atmospheric and noise from other vehicles. The performance of this overall system is astounding compared to other HF mobile stations that I have used.

In the photo you will see a KLM 6 element, 29 ft boom, 10 meter beam in use at Field Day. The 40 ft tower on my motorhome is "self supporting" at 25 feet. I have also hung a three foot wide (two wire) cage dipole for 80 meters just below the beam at about 38 feet and when fed with window line and a tuner, the dipole will cover 80 through 10M.

Thank you for visiting

73,

Terry

10-10 # 27782

SKCC # 651

SPAR