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[KG5JZI]

I'm new to Ham.net and the forum, so excuse me if this has already been asked.  I have a 49 inch 2 meter Larsen whip antenna mounted on the roof of my Nissan Xterra, and I was wondering if installing a shock spring at the base of the antenna would hurt my ability to receive and transmit.  Once again, forgive me if this has already been asked.

[WB6BYU]

The spring would have go between the whip and the base loading
coil.  You may have to trim the length of the whip to account for
the added length of the spring.

[N3IPN]

adding the spring under the whip will change the length above the loading coil... as already stated by WB6BYU, you will need to check the SWR and trim using an antenna analyzer... good luck!

[W4FID]

I have used that antenna on the center of the roof of numerous vehicles over the years. Including SUVs and a couple pick up trucks. Total height from ground to tip of the whip is about what -- 10 or 11 feet? Well below serious overhead obstructions like bride underpasses. I found the whip is flexible enough to not need a spring. I the car in the garage is the issue then the spring won't be the answer anyway. You'll need a fold over adaptor to get the antenna parallel to and just above the roof to clear an 8 foot garage door opening. "Tonked" in many many times in parking garages, trees, etc. As stated already the spring will change the length of the whip. My opinion -- not needed and will cause more issues with antenna detune than it's worth.

[K1KIM]

Does it really perform any better than a much shorter antenna, like the Comet CA-2x4SR, that can utilize a mag mount to couple a ground plane?

I have even just cut a 19" brass rod connected to the mag mount with success.

2M FM is line of sight communication. That's why repeaters are on tall buildings, water towers and mountain tops. Simplex from vehicle to vehicle and home are even more challenging.
100W with a mountain in between is worse than 3W of open space.

That's a lot of antenna sticking up. Garages and low hanging branches of trees come to mind.

[N0ETR]

To answer your question, no the spring will not affect your RX/TX. Just be sure to check the standing waves after you install it, and if needed, trim the whip.

[K1KIM]

To answer your question, no the spring will not affect your RX/TX. Just be sure to check the standing waves after you install it, and if needed, trim the whip.

That is incorrect.

If it affects his SWR dramatically, then yes it will alter his RX/TX.

[KG5JZI]

Thanks for all of the replies.  I appreciate all of the good information.  I might just change over to the Comet CA-2x4SR, as K1KIM suggested.  I'm catching a lot of grief from my wife about all of the "scratches" on the ceiling of our garage.  Once again, thank you all for the information.

[KG5JZI]

One more thing.  I'm assuming that, if I went with the Comet antenna, I would need to replace my Larsen base with one from Comet.  Is that so?

[KG5JZI]

Actually, I meant "mount", not base.

[WB6BYU]

If both use an NMO mount, then the antennas should be
interchangeable on the same mount.

Mounts are relatively standardized, with many different types
of antennas available for each style.

So the question is, do the two antennas use the same type
of mount?

[WA3SKN]

The 49 inch Larsen is a 5/8 wavelength antenna.  If you add a spring you will need to shorten the radiator by the same amount.  Larsen usually uses a "spring steel" radiator so a spring is not needed.
You might not need all that height in your area.  Have you tried a 1/2 wavelength or 1/4 wavelength antenna?  It might be all you need.

-Mike.