Business band 1/4 wave better than Larson?

[KD4UPL]

I recently put a 2m/70 cm mobile in the wife's car. The only antenna I had laying around is an NMO mount 1/4 wave cut for the business band. It's about 17.5 inches long with no coil or anything. I figured it might work okay for 2M. It turns out is has a good SWR on 2M and a good SWR on 70cm. What a surprise.
I figures I could do better so I got a Larson antenna labeled as a "special" on the mount. It's about 18" with an open coil in the middle of the whip. I was told it was a 2m/70cm antenna by the local ham who gave it to me. The Larson has worse SWR on both bands than the 1/4 wave. Both antennas are under 2:1 but I'm really surprised the Larson isn't better.
So, I'll leave the little business band on there.

 

[Moleculo]

You know the old adage: If it ain't broke....

 

[North Texas Mudduck]

the nmo part could be rusted it could be already cut for something else
what does the mfj say.

plenty of dualbanders that are better than a larsen
theres things you have to look for

 

[KC9Q]

That's not surprising! You see a quarter wave antenna for 2M is a 3/4 wave antenna for 440 MHz (i.e. 148 MHz x 3 = 444 MHz). Same principal as a 33 ft vertical is a 1/4 wave at 7 MHz (40 Meters) and a 3/4 wave at 21 MHz (15 Meters). The 1/4 wave will produce 0 db gain, and the 3/4 wave will give about 1.5 dB of gain. You will likely see the same gain specs for the dual band 18" 2 Meter antenna with the air wound inductor in the middle. It's not suprising that the dual band antenna has the same performance as the 1/4 wave whip with the air coiled inductor in the middle when you look at it, is it? You're paying more for the extra machining to get that coil in the middle, when it is basically still a 2 meter quarter wave antenna.

Regarding the SWR. An antenna analyzer will give you a fast answer as to where the antenna is resonant at. Without it, just look at the SWR difference between 144 MHz and 148 MHz. If the SWR is lower at 144 than 148, the antenna is too long and needs to be shortened. If on the other hand it is lower at 148 than 144 it's too short and needs to be lengthened (harder to do), but it will give you better SWR at 450 MHz.

 

[WA8ZYT]

Nothing beats a quarter wave antenna, mounted in the center of the roof, for a mobile antenna. Hard to do on HF though!