Grounded antennas, are they noiseless?

[fjpompeo]

Do anybody know why 2m 5/8 wave grounded antenna is less noise than non grounded ones?
Where can I get a project to try?
73 - PU2PLL - Brazil

 

[flatulent]

I have never heard this. Antennas are passive transducers and so do not generate any noise of their own. These antennas must be worked against a counterpoise and so they are always "grounded."

 

[klug]

There were rumours among radio-amateurs that GP antennas are noisy. At least, I heard that on the end of 70th. There were explanations:
- GP has vertical polarization, and industrial noises have mostly vertical polarization too.
- GP (and all open antennas - where central wire is connected to antenna and is isolated from ground wire) are liable to static collecting. And they are noisy during snowfall (and maybe during thunder).

I was using GP on 10m-40m bands and also short-cuted on 80m. There was feeling of additional noise in comparing with undirected delta loop (horizontal polarization). But maybe it is caused by local conditions (I had strong jammer near me).

73! klug.

 

[dowjones]

hello,

as any other passive component, an antenna generates its own noise, which is equal to the insertion loss (ohmic loss, radiation efficiency or whichever the way you call it). On the other hand they capture cosmic noise, affected by atmosphere, sun, stars, moon,... (remenber the 2.7K background noise)

I dont know nothing about that particular antenna, but if it has less losses than others, it generates less noise than others.

regards

 

[flatulent]

precipitation static

I have just remembered something. If the antenna is not DC connected to ground even through a large resistance (it is AC coupled through capacitors to the receiver) charge can build up on it until the DC voltage gets large enough to arc to the nearest ground. This arcing causes RF noise pulses just like static and lightning.

 

[VSWR]

A DC grounded antenna is a MUST!

If you leave the center conductor of the attaching coaxial cable without a good DC path to ground in the antenna, a lightning strike somewhere in your area might damage your receiver. Even a strike several hundreds of meters away can cause high voltages induced your antenna structure. Today's RF FET amplifiers are very sensitive.