Faced with the problem of developing a useful mobile rig, Larry Riley, W8MIS, of Fenton, Michigan put together this antenna incorporating an SG-237 for tuning.
As Larry says, it is a "home brew base load on 75-40-20 meters. I use a 8 foot fiberglass on the higher bands:
" You can just see the SG-237 mounted under the lip of the truck bed to the right of the antenna. The base loading coil tapped at the base is 60 turns of 12 gauge silver plated wire. I plan to change the wire to 14 gauge enameled and tap at the same point. I works like gangbusters on 75 and 40. It will tune on other bands but no comparison was made with it and the 8 foot fiberglass. (I am sure the 8 foot fiberglass will out perform). So for optimal performance on the low bands I use the base loaded antenna and the 8 foot fiberglass on the high bands. The coil dimensions are 3 inch in diameter and 8 1/2 inch high. Below is a print out of the antenna coil design."
MOBILE ANTENNA ANALYSIS (For mid-mount on standard pickup)
Input Parameters
Coil Data
Resonant frequency: 3.976 MHz
Inductance: 107 uH
Base section length: 1 feet
Reactance: 2672 ohms
Base diameter: .125 inches
Wire size: 14 AWG
Top section length: 5.5 feet
Diameter: 3 inches
Top diameter: .125 inch
Length: 5.9 inches
Performance
Radiation efficiency: 2.7 percent
Relative radiated power: -15.7 dB
Feed-point impedance: 13 ohms
Bandwidth for 2:1 SWR: 27 kHz
Secondary Outputs
Turns: 58.8
Radiation resistance: .3 ohms
Pitch: 10 turns/inch
Electrical length: 10 degrees
Spacing factor: .56
Degree-ampere area: 5.7
Coil 'Q': 310
Over-all height: 10.7 feet
Coil loss: 8.5 ohms
Estimated ground loss: 3.7 ohms
100W I(RF): 2.8 amps
Shunt: 1370 pF (Mica) for 'L' match to 52 ohms
(if not using the SGC coupler).
If a coupler is used no cap at base of antenna.
SGC Inc., Tel:
425-746-6310 Fax: 425-746-6384
Email: sgc@sgcworld.comSGC reserves the right to change specifications, release dates and price without notice.
