No Ground Plane anntenna better for mirror mounts?

[DarrenFishtrain]

It seems magical to me that I can buy an antenna that doesn't care about a ground plane. Reading the forums say they work - so here's the question -- when doing a mirror mount or hood-lip mount where the ground plane is non-existent, or not the best; would a no-ground plane antenna be better to use? I have both a cb and gmrs to mount up. Was going to use a mirror mount on both sides to get maximum separation from them (scanner antenna on roof in the middle) but neither are "no ground plane" antennas... I (now believe is wrong) thought that if the antenna is physically grounded to the body, that this would work; but now am thinking that it must be on a ground plane, so going "no-ground plane" antennas would be better?

 

[roadranger]

Depending on the vehicle...

...the mirrors are already grounded, like this one. If it is like the next one, you will have to mount them some other way. I clamped two antennas (not show in this picture) to the roof rack on the car. Once the antennas are clamped to the mirror mounts (like on the big rig), it will be a better ground. Magnet mounts work similarly. The screw on the bottom of the antenna mounted, is the ground on the same antenna. The ground is simply the other end of what is a dipole antenna.

 

[jassing]

Thanks roadranger -- the question comes from the (seemingly standard) response of "an antenna mounted on a mirror is a poor ground plane" -- So, the question then is -- would using an antenna designed for use w/o a ground plane work better than an antenna expecting a quality ground plane?

Is an NGP antenna better than an antenna+bad ground plane? or is a ground plane antenna with *any ground plane* better than an NGP antenna?

 

[LtDoc]

Lots of misconceptions about those "groundplanes". A "groundplane" consists of the 'other half' of a typical mobile antenna. It should have something close to the right characteristics for it to work well. I hear a lot about mirrors being a bad 'groundplane' when they really don't have to be 'bad' at all. If they are electrically connected to the rest of the vehicle, it isn't just the mirrors but the whole vehicle that's the 'groundplane'. That 'groundplane' may not result in the most desirable radiation pattern for an antenna, but it will certainly work. You have to work with what you have available for mounting an antenna. If those mirrors are all that you can use, then use them.
The 'NGP' antennas do have an 'other half', it just isn't very apparent. Most (if not all of them) use the feed line as the "groundplane" or it's 'other half'. They are primarily for use where there's no practical way to find any metal, as in fiberglass vehicles for instance. They do work. How well you can do the installation and route that feed line will determine how well they will work. Are they better than other types of antennas? ONLY in particular circumstances, in general, they are not -the- way to do it if you can help it. (A pair of 'left-handed' scissors are the best answer for all people, just the left-handed ones, you know?)
- 'Doc

 

[jassing]

Thanks doc -- that brings me back to my "gut" .. I was just so overwhelmed with the "that's a crappy ground plane" -- and that was it.... the "why is it a bad" never got answered -- indeed, I described how I planned on mounting my antenna (to the back of the cab of the truck) and was told "bad ground plane" -- but then I was shown a picture of an antenna attached in the same method to a toolbox in the bed -- lower than i was going to mount -- but I asked "why is that better" -- nadda.
It's all a moot point at this point -- I have already drilled & mounted - all seems ok.
But I appreciate your posts -- makes me feel better about what I've been doing for all these years.
-josh