Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1] 2 Next   Go Down
  Print  
Author Topic: 6" Or Shorter 2m Antenna?  (Read 7850 times)
KD7ZYW
Member

Posts: 1




Ignore
« on: January 15, 2011, 10:33:46 PM »

We just got a 2011 Mazda CX-9 and I'm trying to figure out how to put an antenna on it for APRS and other 2m use. My problem is the car parks in the garage and I only have about 6" of clearance when entering the garage. I'm trying to find a short antenna that I can put on the roof and not have to fold down.

Thanks,
Josh
Logged
VA3WXM
Member

Posts: 277




Ignore
« Reply #1 on: January 16, 2011, 05:14:51 AM »

Something like a Comet SBB-1 which stands 16" is apparently rubber-coated and flexible.  The Comet B-10 is 12" tall but not flexible.

I think you'll be hard-pressed to find a 6" tall 2M antenna that isn't made for handheld use.
Logged
W8JX
Member

Posts: 5452




Ignore
« Reply #2 on: January 16, 2011, 05:45:52 AM »

Also consider that if you found and used a 6 inch loaded antenna on 2 meters it would be a negative gain antenna and likely be down at least 4 to 6 db on transmit and receive and possibly even more.
Logged

--------------------------------------
Entered using a  WiFi Win 8.1 RT tablet or a Android tablet using 4G/LTE or WiFi.
WB6BYU
Member

Posts: 13020




Ignore
« Reply #3 on: January 16, 2011, 05:58:53 AM »

A friend of mine only had 2" clearance under his garage door.  He used a standard springy quarter
wave whip and it survived years of bending on the way in and out.

There are a number of commercial VHF antennas that are low enough - I've heard them referred
to as "sharp fins" (long and skinny) and at least one manufacturer made a 2m version of the DDRR
that is about 6" in diameter and 4" tall.  They tend to be high Q antennas, so the SWR bandwidth
might not cover the whole band, but they can be tuned to the range of interest.  (I've got one
around here somewhere...)  I think one was called the "Un-tenna".

Or you could put a 5/8 wave whip on the hood - a longer whip mounted lower on the car so it
has the same top height would bend more easily.  I even remember seening a quarter wave whip
mounted on the front turn signal of a VW bug back in the day - there are lots of ways you can
make it work.
Logged
AD4U
Member

Posts: 2153




Ignore
« Reply #4 on: January 16, 2011, 06:01:32 AM »

I don't know what kind of vehicle this is.  Maybe a small SUV?  You would be MUCH better off by installing a 1/4 wave (19") antenna on the side of the engine cover (hood) near the windshield.  Several manufacturers make a little chrome or SS bracket shaped kinda like an L or you can easily make one yourself.  Drill two small holes out of sight in the metal lip that goes under the hood edge.  Screw the L bracket to the vehicle via these two holes.  Mount the antenna to the L bracket.  When installed it will look like a broadcast radio whip antenna.  This will work MANY times better than a 6" antenna.

Don't worry about resale value of your vehicle because of the two little holes in the metal lip UNDER the hood.  They can easily be covered when time to trade the car and they are completely out of sight unless the hood is raised, and even then nobody will notice them.

Dick  AD4U
« Last Edit: January 16, 2011, 02:28:43 PM by AD4U » Logged
KC8IUR
Member

Posts: 156




Ignore
« Reply #5 on: January 16, 2011, 06:38:14 AM »

Why not just get a NMO and unscrew it when you enter a parking structure?
Logged
AJ3O
Member

Posts: 124




Ignore
« Reply #6 on: January 16, 2011, 07:54:14 AM »

How about one of these. I saw it while doing some research.


http://www.rfparts.com/diamond/k9000photos.html
Logged
K0BG
Member

Posts: 9840


WWW

Ignore
« Reply #7 on: January 16, 2011, 08:02:22 AM »

Dick has the best solution, I believe.

One thing to keep in mind about garage clearances, and roof mounted whips is this; clicking the antenna against the door opening as you back in and out won't destroy most 1/4 antennas. However, if the whip drags across the inside of the garage door when it opens and closes, you run the risk of catching the whip between the door panels. If this occurs, it is possible to destroy the antenna, and to even pull the mount through the roof panel with predictable results.
Logged

WX7G
Member

Posts: 5919




Ignore
« Reply #8 on: January 16, 2011, 11:26:53 AM »

Here you go, the TRAT1420. It's 3.3" tall:

http://www.wpsantennas.com/trat1420-antenexphantomlowprofile142-160mhzvhfunitygaintunableantennawhitewithpatentedfielddiversity.aspx




Logged
KD4LLA
Member

Posts: 450




Ignore
« Reply #9 on: January 16, 2011, 02:22:40 PM »

Drill a hole, put an NMO in roof w/ a 19" quarter-wave whip on it.  Last time I bought a whip it was $8 at a radio shop.  Leave the antenna in place when you trade or sell the vehicle.  The antenna will bend or move whenever it needs.  The one I have on my minivan has been on for five years and in and out of the garage.  I am constantly amazed at the folks who fail to see that a properly installed, roof mounted 19" whip will out perform *any* so called gain antenna, and will take abuse year after year.

I have seen what happens when something hits one of the low profile antenna's.  Way more damage than that quarter-wave whip will ever cause.

Mike
Logged
N3OX
Member

Posts: 8852


WWW

Ignore
« Reply #10 on: January 16, 2011, 07:03:17 PM »

Also consider that if you found and used a 6 inch loaded antenna on 2 meters it would be a negative gain antenna and likely be down at least 4 to 6 db on transmit and receive and possibly even more.

That's not necessarily true. 

A six inch tall antenna with good top loading and a shunt inductor for matching to 50 ohms should be able to cover the 144.39-148MHz range under 2:1 SWR.  It will have good efficiency, provided the ground connection to the roof is really good. 

Rubber-ducky style loading with a small, distributed coil embedded in rubber is not what you want to do. 

A good capacitance hat with spokes and perimeter wires in the 7 to 8 inch diameter range is enough to load a 5.5 inch whip to near resonance (leaving it a little capacitive so that the shunt coil across the coax works), and this antenna should be within a fraction of a dB or so of a full size quarter wave whip if the ground connection is excellent (<1 ohm, maybe doable).

A piece of #18 wire bent into a shorted transmission line stub about a half inch wide and 3/4 inch long would work for the stub.

I'd probably do "bendy 1/4 wave whip" myself but if you really wanted to build a six inch tall 2m antenna you could do it.  Tuning will be pretty critical to cover both the APRS frequency and all the repeaters with < 2:1 SWR but you probably don't need to even be below 2:1 for some 2m mobile rigs.


Logged

73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K1CJS
Member

Posts: 5871




Ignore
« Reply #11 on: January 17, 2011, 05:10:15 AM »

What you're probably looking for is called a 'stealth' antenna.  The post by WX7G gives a website address of such an antenna.  It costs ten times as much as a quarter wave NMO mount whip, but if that's what you want.....
Logged
VA3WXM
Member

Posts: 277




Ignore
« Reply #12 on: January 18, 2011, 12:10:53 PM »

The Phantom antenna line will work but not they're not that at great on VHF.

Another option might be a "transit-style" antenna which almost looks like a stapler.  They're a little pricey but are well built (most railroads use them on their locomotives).
Logged
KQ6Q
Member

Posts: 965




Ignore
« Reply #13 on: January 18, 2011, 08:30:31 PM »

I have a Honda Element and the garage at work has 6'6" clearance. I mount my 2m/440 antenna on a bracket that comes out of the hood opening on the left front fender. It's a homebrew bracket,so I use a very short 2m/440 antenna, previously used at the top of the hatch on a Dodge Caravan. It gets the job done. I have a much longer antenna that fits and will work, but it flails a lot in the wind above 30mph, so I keep it in the vehicle for use when I might need it
Logged
K8KAS
Member

Posts: 569




Ignore
« Reply #14 on: January 24, 2011, 06:23:42 AM »

Has no one heard of the 100 year old Inverted L, you bend the antenna 90 deg at 1/8 WL or around 9 inches. Very effective and the hi current is still vertical.  No loading coils or other junk needed. I have done this a number of times for clearance, worked as well as the fully vertical 1/4 wave.. KISS,, right guys....Denny K8KAS 73
Logged
Pages: [1] 2 Next   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!