[Antennas] 1/2 wave & 5/8 wave 144 mhz mobile antenna

Tue May 9 12:57:44 EDT 2006

The 1/2 wave does not require a ground plane or connection to ground.
That is why they are used in marine applications since many boats are 
fibreglass. The 5/8 wave does require a ground plane. I have successfully
used a 1/2 wave mobile antenna up on a push-up pole with no ground 
connection into a mobile rig running a 50 watts for a bicycle race. SWR 
was < 1.2:1. I have used the same antenna mounted on a wall next to a
window when I was operating out of a shelter after the hurricanes.
The nulls you hear are from path losses or obstructions (buildings, hills,etc.) 
between you and the repeater or simplex station. It is not a function of
grounding especially if it is in the same locations for both antennas. 
The swr on the 5/8's will probably come down when it is grounded.
You can run a wire from the base of the mount to elsewhere on the frame
or body and not have to mess the paint up even on the underside of the trunk
lip.
73,
Jon
KD5SFA
-----Original Message-----
>From: Myles <mpb1 at comcast.net>
>Sent: May 8, 2006 3:41 PM
>To: antennas at mailman.qth.net
>Subject: [Antennas] 1/2 wave & 5/8 wave 144 mhz mobile antenna
>>Over the past few weeks I have been involved with installing a antenna and a 
>2 meter rig in my car - Finally finished today - on my shake-down-cruise I 
>noticed the following:
>>5/8 wave antenna gives me a better receive sig.
>>1/2 wave is shorter with lower sig level but less prone to hitting tree 
>branches - so this I can live with.
>>I notice that with either ant (5/8 or 1/2 wave) I get deep nulls in signal 
>level as I drive along.
>>I did not notice this effect in my previous car - I used the same two 
>antennas - only difference was the mount. In my old set-up I had a lip mount 
>on the trunk and the mount was grounded via the set screws.
>>In my new set-up I am using a Diamond (HRKS) mount on the roof - it is a 
>stick-on non ground mount. From what I have read a 1/2 wave or 5/8 wave 
>antenna can operate with out a ground or a ground plain - is this a fact, or 
>would I be better served if I grounded the mount ?
>>I should be able to remove some paint from a hinge bolt on my rear tailgate 
>and run a short strap to the 259 connector on the mount. I would like to 
>hear some comments on grounding first - the bolt and paint deal is not an 
>easy project.
>>Antennas: The 5/8 is a Larson the 1/2 wave is a Diamond NR770HA (144/440)
>>Questions are:
>>Should a 1/2 wave and a 5/8 wave mobile antenna be grounded ?
>>The deep nulls as I drive along (slow speed) in traffic - is this an 
>indication of a poor install or no ground?
>>I have not measured the SWR ( do not have a meter for 144mhz) will grounding 
>alter it ?
>>This should be the last of my problems installing a rig in a 2005 VW Passat 
>wagon.
>>Thanks for reading this
>>Myles - W1IKO 
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