Batboard

Looking for info on antenna whip length for larsen nmo mount antenna.
Antenna is VHF high band, whip is currently 46".
Needs to be cut for around 155 mhz.
Does anyone know the correct length or the web location of a cutting chart. Larsen doesn't have anything on their web site.

Thanks.
Dale

According to the Larsen cutting chart I have, 46" is at 152 MHz, so you're lucky, you still have enough whip. (I'm assuming you're using the NMO150 coil, and not something non-standard.)

For 154MHz, the length is 45.5" and 156MHz is 45". So it's reasonable to assume it should be 45.25" for 155MHz. I'd go with the 45.5" and use an SWR bridge to fine tune it. Just my way of doing things, though the cutting chart is usually pretty close.

I'll tell you though, it's probably not all that critical. I have an NMO 150 coil and a whip cut for 147MHz, and the 1.5:1 SWR bandwidth is 145MHz to about 152MHz. I've checked it. So you cut for 45.5" and it should be fine, and will allow some room for pruning as needed. Of course the variable will be whether it's a magmount, where on the car it is, etc. Mine is mounted in a hole on the trunk deck.

Good luck,

Chris

Ive used this web page before with good results. Good luck.

~Chad

http://www.qsl.net/kb5wck/antenna.html

For a 5/8 wavelength antenna:

whip length (in inches) = 535 / frequency (in MHz)


For a 1/4 wavelength antenna (including spring, etc...)

length (in inches) = 234 / frequency (in MHz)

Curt, K8AI

Curt, don't those formulas give the length in feet, not inches?

Those formulas give their answers in feet, not in inches. For the benefit on the mathematically challenged, you have to multiply the results by 12 to get the answer in inches.

Tom, W2NJS
...in D.C