Isolate A99 Antenna from Mast Pipe

[loosecannon]

Paul,

do we agree that we can interchange the terms "ground plane" and "counterpoise" in this example?

in other words, can we agree that the radials on these antennas are providing an artificial ground IE "other half of the antenna"?

if so, then we can agree that there is a capacitive ground being used, and by connecting one plate of that capacitor (radials) to the other plate (actual ground level) with the support structure; that we are messing with that capacitance?

LC

 

[loosecannon]

well it looks like this thread has died on the table waiting for answers, so i will try to do my part of the thread CPR.

The following paragraphs are direct quotes from The Department of the Army manual TM 11-666 titled "Antennas and Radio Propagation".


Ground-Plane Antenna:

A ground plane antenna consists of a vertical radiator which, in effect, carries its own artificial ground. the artificial ground or ground plane consists of a flat disk of metal or a number of metal rods or spokes located at the bottom of the radiator and usually at right angles to it.
Since the metal disk or spokes are not connected directly to ground, they may be referred to as a counterpoise. This term is used rarely, however, this part of the antenna usually being called simply an elevated ground plane.


(now we will back up to address the term 'counterpoise')

Counterpoise:

A counterpoise may replace the usual direct ground connection in which current actually flows to and from the antenna through the ground itself. the counterpoise consists of a structure made of wire erected a short distance off the ground and insulated from ground.
The counterpoise operates by virtue of its capacitance to ground. because of this capacitance, the ground currents which flow normally and usually are collected by conduction now are collected in the form of charge and discharge currents. the end of the antenna which normally is connected directly to ground now is connected to ground through the large capacitance formed by the counterpoise.
If the counterpoise is not well insulated from ground, the effect is much the same as that of a leaky capacitor. Leakage currents flow between the counterpoise and ground so that a poorly insulated counterpoise introduces more losses than no counterpoise at all.

(now back to ground plane antennas)

Any desire to operate such an antenna in conjunction with the actual ground would create high ground losses and would prevent efficient radiation or reception. The ground plane antenna, on the other hand, is usually well elevated so that ground losses are minimized. (yes, this does mean that the higher in the air you get your antenna, the less this all matters)
The elevated ground plane also prevents circulating currents from flowing in a vertical mast that might be used to support the antenna. these currents, if not prevented, would cause the vertical support itself to radiate in the same manner as a long-wire antenna. As a result, undesired high angle radiation would be produced.


As always, i could be misinterpreting something, and am open to being shown the light.
LC

 

[Meglotron]

i dont see a half wave as a groundplain but you can read online about it only needing short radials if any, like 2 feet is all but yes isolated

 

[BOOTY2]

does the polyphaser use a ground wire to earth ? if so , doesn't that defeat the whole purpose of insulating from the mast ?

 

[fourstringburn]

does the polyphaser use a ground wire to earth ? if so , doesn't that defeat the whole purpose of insulating from the mast ?

If you mount and use it like this it does. This what I use for all 3 of my antennas. This bonds the coax shield and polyphasers to the same ground point.

 

[BBB]

This antenna isolation topic comes up from time to time locally as well. I run a Sirio 2016 aluminum vertical antenna on a few sections of military FIBERGLASS antenna mast. The non-conductive fiberglass mast is mounted to my wood framed chimney that in itself houses a steel fireplace flew that goes down to a fireplace about 30' below. This puts the base of my antenna at 36' above grade.

So my aluminum antenna is not mounted to a conductive mast, but may couple capacitively to the steel flew pipe about 4' directly under it. The Sirio 2016 is somewhat unique in the fact that it has (16) 24" ground radials at it's base. For whatever reason, this set up has served me very well for many years now with low receive noise and a good RF take off angle.

Only problem is this white stuff keeps sticking to it in the winter. Need to fire-up the Henry and melt some snow

 

[BOOTY2]

very popular and FWIU durable antennas . played with four 1/4 wave ground elements vs eight 1/8 wave ground elements and got better performance with full 1/4 wave ...... results do vary . would be interesting to mod a 2016 to using 4 1/4 wave ground elements and compare to it's stock version ..... but the smaller ground elements allowing a smaller footprint is attractive to some folks and full size elements won't work for some folks installs .

looks like it's up there pretty good , should be doing very well for you .