Ground Plane...

[southview]

Can coiling the coax under the antenna's magnetic base act as its ground plane? Taking the place of a car roof or a metal plate?

 

[jwt873]

Never heard of coiling up the coax. I doubt it would be very efficient.

Not sure how you plan to mount the antenna, but, you can build a usable vertical antenna without a ground plane or radials by folding the outside braid of the coax back.. This is called a 'bazooka antenna'. VE3VDC Emergency 2 Meter Vertical Bazooka Antenna

 

[krokus]

Can coiling the coax under the antenna's magnetic base act as its ground plane? Taking the place of a car roof or a metal plate?

It could work, but will be adding a significant length of cable, so added loss of signal. Also, the tightness of the coils, near the center, could the minimum turn radius for the cable, possibly damaging the cable.

If you want to do this, use a separate section of scrap cable.

 

[prcguy]

That won't work very well. A ground plane of 1/4 radials will have half the RF currents distributed among all the radials and the RF will instantaneously be going in opposite directions outward to the ends of the radials then back towards the feedpoint for each RF cycle, canceling radiation in the radials. A large ground plane of sheet metal like a car roof would have a similar thing going on but without a predictable cycle from the feedpoint to the end of the car roof.

Having no ground plane will cause the coax to be the other half of the antenna with RF currents flowing on the outside shield. The RF will travel down the coax to the radio then bounce back toward the antenna and any coils will alter the current flow depending on if you have created resonant points along the coax by coiling it and causing premature reflections before the radio end.

Bottom line is don't do it and get some metal under the antenna.

Can coiling the coax under the antenna's magnetic base act as its ground plane? Taking the place of a car roof or a metal plate?

 

[mmckenna]

Taking the place of a car roof or a metal plate?

If you don't need the magnet to hold the antenna in place, as in this is going to be inside, in an attic, etc. then just lay some aluminum foil under the antenna.

 

[southview]

Never heard of coiling up the coax. I doubt it would be very efficient.

Not sure how you plan to mount the antenna, but, you can build a usable vertical antenna without a ground plane or radials by folding the outside braid of the coax back.. This is called a 'bazooka antenna'. VE3VDC Emergency 2 Meter Vertical Bazooka Antenna

Thanks for the link. Tuning an Antenna is simple and at the same time extremely complicated!

If you don't need the magnet to hold the antenna in place, as in this is going to be inside, in an attic, etc. then just lay some aluminum foil under the antenna.

That was sorta the essence of the question, could the grounding braid radiate enough back into the antenna to make any difference hence making it a ground plane?

If you don't need the magnet to hold the antenna in place, as in this is going to be inside, in an attic, etc. then just lay some aluminum foil under the antenna.

To simple!

 

[mmckenna]

That was sorta the essence of the question, could the grounding braid radiate enough back into the antenna to make any difference hence making it a ground plane?


To simple!

I ain't too proud of this one, but we had a major fire and I had to set up a temporary dispatch for our PD at a remote location. I had to do this until I was able to find a more appropriate solution to get them on the air:

1/4 wave VHF antenna on an NMO mag mount, slapped on a piece of sheet metal I found. Worked fine to get into the repeater.

 

[Duckford]

I ain't too proud of this one, but we had a major fire and I had to set up a temporary dispatch for our PD at a remote location. I had to do this until I was able to find a more appropriate solution to get them on the air:

1/4 wave VHF antenna on an NMO mag mount, slapped on a piece of sheet metal I found. Worked fine to get into the repeater.

Reminds me of stories I've heard from some kids who would use cookie tins and tin foil to make home made ground planes to make their antennas functional enough just to get on the air. Go find something reflecting and make it go!

 

[jwt873]

To the OP.. What are you intending to do? (That will help with suggestions). Do you have a vehicle with no metal roof?

If so, half wave antennas get get by with no radials or ground plane.. https://www.arcantenna.com/collecti...XDC4ncLPThMjyy8bqf3vnIu1HxITYd1hoCRnQQAvD_BwE

 

[southview]

Thanks, I was just trying to get a signal boost from inside a room to the outside. A radical idea : ) Guess I need an outside antenna, after all, no free lunch!!