Cobra ST 75 CB with 4ft Firestik Antenna (6/7)
TUNING YOUR ANTENNA (For more information see Firestik Tech Help)
Setting the SWR of Your Antenna© - Firestik® Antenna Company
The goal is to have your CB operate at an SWR of 2.0 OR BELOW.
IF SWR IS RED ON ALL CHANNELS – DO NOT OPERATE YOUR CB; YOU WILL RUIN YOUR ELECTRONICS!
SWR below 2.0: Your radio can be operated safely.
SWR above 2.0 but below 3.0: either a bad quality cable, insufficient ground plane or ungrounded antenna mount.
SWR above 3.0: Likely a short in your coax connectors or the mount is installed incorrectly and shorts.
Steps to take an SWR reading:
1) Antenna connected to "ANT" side.
2) Set to “10W”.
3) Set to” FWD”.
4) Turn calibration knob all the way counter clockwise.
5) Turn on your CB.
6) Set your CB to channel 1.
7) Press the "Talk" (key) button and keep the button pressed for the next couple steps.
8) Turn the calibration know until the needle goes all the way over to the far right side and lines up with the "SET" mark.
9) Flip the switch to "REF".
10) Record the reading (the decimal scale is under the main scale).
11) Let go of the "Talk" button.
12) Repeat steps 7 through 11 for channel 19 and channel 40.
Adjusting a LONG antenna:
If the SWR on channel 40 is greater than that on channel 1, your antenna is considered to be "LONG" and reduction of physical height and/or conductor length will correct this situation. Depending upon antenna model, this entails screwing down the tunable tip, or, removing the tip, making short slits in the plastic covering and unwinding and clipping off wire. Firestik Designer Series antennas require loosening the allen screws and lowering the metal whip.
Adjusting a SHORT antenna:
If SWR on channel 1 is greater than that on channel 40, your antenna is considered to be "SHORT" and increasing the physical and/or electrical length of the antenna is required to correct this situation. Because we make our antennas extra long, readings which indicate "Short" normally stem from ground plane deficiency (lack of vehicle metal surface for the antenna to reflect its signal rom). This condition is often corrected by adding a spring and/or quick disconnect to increase the physical height. Ground plane deficiencies can also be compensated for by using dual (co-phased) antennas or special no-ground-plane antenna kits.
Lengthening of the Firestik II and Firefly is accomplished by turning the tuning screw further out. On Firestik and Road Pal models, it requires tip removal, short slits in the plastic covering and, the separation and upward repositioning of three or more wire turns. Firestik Designer Series antennas require loosening the allen screws and raising the metal whip.
NOTE: The shorter the antenna, the more sensitive it is to adjustments. For example, removing two wire turns on a 4 foot antenna might move the SWR by 0.3; the same amount removed from a 2 foot antenna may move the SWR by 1.0. Make smaller adjustments on shorter antennas.