Homebrew 2m/70cm Center Loaded Mobile Antenna Project

[N4WRD]

Hey all,I've been searching for some info on building a dual-band mobile antenna for 2m/70cm with a center loaded design and I've had no luck. I know commercial antennas like this are inexpensive, but I want to build one. Anyone have any info on a project like this?Thanks in advance!73Scotty | N4WRD... never in reverse!

[WB2WIK]

Those aren't really "center loaded."

The "bump" in the middle of these mobile whips is a phase shift network on 70cm that allows the upper and lower elements to radiate in phase, and it's almost transparent except for the small amount of inductance it adds on two meters, which shortens the overall length of the antenna for 2m slightly.

[K7JEM]

To clarify what Steve said, this antenna is essentially a 5/8 over 5/8 antenna on 440, and a half wave antenna (electrically) on 2M. Both of these antennas are high impedance when end fed. The base "coil" is a matching network that steps up the impedance on both bands so that the 50 ohm coax will match the high impedance radiator. They work pretty well, with 2M performance approaching that of a similar HW mobile antenna, and the UHF part very close to that of a single band 440 antenna. That accounts for their popularity. Most people will never notice a degradation, although there is a slight amount, probably around a dB or so.

Joe

[WA7KKP]

If you want a really cheap 2/70 dualband antenna, a quarter wave stinger works pretty good on both bands. 1/4 wave on 2 meters, and a 3/4 wave on 70cm. Can't get much simpler or cheaper than that.

Same thing works on 6/2 meters. I used to use a 54" whip which was a 1/4 wave on 6; 3/4 wave on 2 meters. The 3/4 wave antenna radiated rather high, but with repeaters, that didn't seem to be much of an issue.

Gary WA7KKP

[N0UYR]

If you can find someone with some older copies (late 70's to early 90's) editions of the ARRL Handbook I think they used to have something like this in them. I can recall a 2M 5/8 wave and an on-glass dual-band I think. I'll have to check. If you are an ARRL member try the on-line QST article search, It may take some different phrasing to work but they had to have done something back then.