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Author Topic: Super-small 2 meter anrennas  (Read 1836 times)
N7KTX
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Posts: 31




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« on: July 15, 2012, 04:25:14 PM »

I want to install a 2-meter rig in my commercial-use vehicle (a Sprinter van) but I can't allow the distracting appearance or the increase in clearance height of a whip antenna.   The vehicle is used in urban circumstances with many repeaters nearby, so the need for long range capabilities is minimal.

I noticed a very compact stub antenna made by Laird (TRAT1420, TRABT1420) listed in AES, but couldn't find any links re performance.

Has anyone out there tried this antenna?  Even the QST archives are silent, which makes it hard to risk the purchase price (<$100.00 US).  But who wants to flush 100 bucks for nothing?

Dave
KF7OAE
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WB6BYU
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Posts: 13337




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« Reply #1 on: July 15, 2012, 05:34:09 PM »

There are a number of such very small antennas sold into the VHF-HI land mobile service.
I suspect you haven't found many ham reviews because few hams need that short of an
antenna, and can get a quarter wave whip for much less.

Larsen makes a line of antennas less than 4" tall in the 150 - 175 MHz, though each model
is only rated to cover a 2 MHz range, and they don't have one for 2m.

The Laird antennas are tunable over 142 - 160 MHz, with reasonable gain (or at least
not too much loss), but don't say what the operating bandwidth is at any one setting:

http://lairdtech.thomasnet.com/viewitems/vehicular-mobile-radio-antennas/phantom-antennas?&bc=100|3001622|3001654|3001655

I expect the bandwidth is similar to the Larsen, but it would be worthwhile finding
out from the manufacturer.

There are other ways of building very short antennas.  The mos common is the DDRR,
which is often known commercially as a "blade" or "IFA" (Inverted F Antenna).  These
also can have a wide tuning range but relatively narrow bandwidth once adjusted.  A
ham version of the DDRR was marketed as the UNtenna for a while:  I have a mag
mount version, but one that goes on an NMO mount would be much more efficient
due to the high currents flowing to ground.  I've also made my own DDRR about 2" high
using copper pipe, and have some round brass sheets on hand to try an improved
version some day.

If you want a REAL low profile antenna consider an "annular slot".  This could be cut
into the metal roof, or on a printed circuit board that fits into larger hole in the
roof.  It adds ZERO height, unless you need to add a waterproof coating over
the top of it.  That's what the FCC monitoring sedans used so there was no
visible antenna on the car - it was built into the roof.  Gives you vertical polarization
without any vertical height.  But that's probably more effort than you want.


On the other hand, a thin quarter wave wire or piece of adhesive copper foil tape
(as is used for burglar alarm systems) running up the center of the windshield
and fed against a couple ground radials or the vehicle body would not add any
height or require any modifications to the vehicle, and it would be cheaper.
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N7KTX
Member

Posts: 31




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« Reply #2 on: July 15, 2012, 07:50:19 PM »

Thanks very much for the info, WB6BYU.  Very helpful link as well!
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K9KJM
Member

Posts: 2415




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« Reply #3 on: July 15, 2012, 08:43:05 PM »

I suggest a "Rare Earth" magnet dual band antenna, With 9 feet of slim coax from Tower Electronics, With the connector of your choice to fit your radio:

http://www.pl-259.com/page6.html

At only 17 bucks these things really work great!  Very unobtrusive skinny whip that is not very noticeable at all.

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N7KTX
Member

Posts: 31




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« Reply #4 on: July 15, 2012, 08:45:31 PM »

P.S.     Further investigation puts the bandwidth for the Laird TRAT1420/TRABT1420 at 1 MHz.
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