[Fwd: LF: Mystery: my antenna needs no radials!]
Sat, 29 Aug 1998 15:28:59 -0400
Hans-Joachim Brandt wrote:
> Toni Baertschi schrieb:
> > >From HB9ASB:
> > I have made some tests with my ground system and the results are very
> > strange: When I disconnect the whole radial network, the antenna current
> > doesn^rt change very much (About 3A for 300W RF). It seems to me, that I
> > do not need any radial, despite the fact that I live on sandstone!
> > So far, I have only one explanation for this phenomena:
> > Here we have already three networks in the ground: The main power
> > supply, the cable TV and the water supply (fortunately still with Iron
> > pipes). The shielding of the CATV and the ^dearth^s of the mains are both
> > connected to the water supply. As my TX is still connected to the
> > ^dearth^s of the mains, I can profit from this large ground system and I
> > imagine that this is much better than all the radials I^rve laid out in
> > the garden.
> > Maybe this is the key to the mystery that some stations have low earth
> > resistance without much additional grounding and others hardly get under
> > 100 Ohms. Maybe, in these cases they have no CATV, plastic water pipes
> > and the mains in the air (almost at the same height as the antenna)?
> > 73 de Toni
> Here at DJ1ZB at first I have built a ground system made of 28 insulated radials
> of different lengths (10 to 30 m) in my garden, mostly on lawn, and have
> measured a ground resistance of about 80 ohms.
> I have even lifted this radial system to at least 30 cm or one feet above ground
> and have measured the same "ground" resistance.
> When I connect the centre of this system to my house ground, however, the total
> ground resistance inceases to 120 ohms. As reported further, this sensitivity to
> the connection of separate grounds is more pronounced with the elevated ground
> Rather late I decided to measure the ground resistance of the house ground
> alone, connected directly in the cellar: 75 ohms! This ground is also connected
> to the water supply net, of course.
> Therefore I can also say that I should be able to live without the additional
> radial system. The only reason against the use of the house ground would be EMC
> problems in the house when transmitting.
> When I want to use the insulated ground system effectively (presenting 80 ohms
> ground resistance) but still want to have my equipment in the shack grounded to
> the safety house ground I have to employ a matching transformer to the aerial
> (from 50 ohms to around 100 ohms, including ground loss 80 ohms and antenna
> variometer loss of 20 ohms) with two separate windings to have both grounds
> separated. The same problem had also been reported by Peter Martinez, G3PLX.
> But on the other hand I think we should clear the different behaviour of
> grounded and insulated ground systems and what could be done to combine them
> effectively. At first it seems to look odd that they cannot be simply paralleled
> for improved performance.
> Rik, ON7YD, with whom I have direct correspondance on some aerial problems, has
> proposed to measure the currents into combined grounded and insulated ground
> systems separately and to check if they might differ in phase. As long as we do
> not have a LF licence here in Germany I will try to prepare for this using
> qrppppp power, but OMs with LF licence and sufficient power in the aerial should
> have less problems employing current probes.
> 73 Ha-Jo, DJ1ZB