Hi Alan,
Well, i expect the oxide film losses of the foil should be neglectible,
compared to the ground losses. And one has the advantege to reach a high C that
is easy to adjust/modify and cheep and that has no overvoltage and heating
problems. Aren't the radials of a LF vertical not almost the same, in
principal? I mean, one electrode of a HV capacitor with a lossy dielectricum?
;-)
Using a HV capacitor or coax cable is also a good choice, of course, but it may
be difficult to get proper C at those voltages. And if we are talking about
connecting the end of a inv L antenna to ground (here: soil) the next question
is: Where do you connect the second electrode of your C? A coax, say RG213 may
be connected to the antenna wire with the inner line. But where do you connect
the screen? Bringing it back to the shack and connecting to ground would mean
not to use the soil as the conductor any more and throwing the coax just on the
bottom would be nonsense since then, one could just take a standard wire which
is principally almost the same like aluminium foil. Using such a simple wire
would mean to require 100s of m of cable to get the same C. And in such a
configuration a high C to ground is essential since one wants to have a
practicable small L for resonance (to handle the losses).
Therefore i had the idea just to try a real loop that needs just a high C with
less voltage (probably <1kV).
If we assume a inv L of 10m hight and 50m horizontal section and make a
rectangular loop out of it, the XL will be in the region of 15 Ohm (?). Then a
C of abt 1µF will resonate the loop. Applying 100W and assuming 2 Ohm losses
will produce abt 7A and a voltage of 750V above the C, no problem to find such
a C :-) Starting with a closed loop is much easier since no L and maybe even no
R transformation is necessary. And with a horizontal section of <50m, the
increased loop area when using the ground/soil may be not really much more, but
with the disadvantage to need a L with a high R and/or less Q...
Markus/DF6NM has also good ideas but i do not want to tell his ideas. Markus?
Go on! ;-)
Stefan/DK7FC
________________________________
Von: [email protected] im Auftrag von ALAN MELIA
Gesendet: Di 23.02.2010 13:31
An: [email protected]
Betreff: Re: AW: LF: VLF_8.79 kHz
Hi Stefan, I am not sure about your aluminium foil idea. I worry that this will
form a lossy capacitor because the dielectric a think film of ali oxide will
break down in places at this voltage and also there is the inknown of the
contact with the ground. I would rather use some UR67 it can be a length
unsuitable for real feeder work (I uses coax as a capacitor in an HV pulse
generator many years ago and though the spec is 6kV it certainly survived 15kV
with no burns though the dielectric. Rik and I discussed this format at length
many years ago for 136kHz but I dont think either of us did any tests.
I would suggest an HV capacitor might be the alternative old TV EHT type??
Actually grounding the remote ends is a lot easier and a lot less to carry if
you are operating "portable"
Alan G3NYK
--- On Mon, 22/2/10, Stefan Schäfer <[email protected]> wrote:
> From: Stefan Schäfer <[email protected]>
> Subject: AW: LF: VLF_8.79 kHz
> To: [email protected]
> Date: Monday, 22 February, 2010, 23:36
> Rik, Alan,
>
> I think we think about the same: using the inv-L as a
> vertical loop by using the ground.
>
> Wouldn't it be easier to use a aluminium foil to get proper
> C (to ground), especially when talking about high voltages
> and high currents? Just covered with some soil and easy to
> adjust/modify...
>
> Stefan
>
> ________________________________
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