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On 73kHz I originally used nylon strimmer cord as the antenna insulator. Worked fine until one day I was testing using PSK (100% duty cycle, long transmission) with G4GVC and it was raining. The antenna fell down and I found the nylon had melted due to HV tracking. Replaced with a ceramic dog-bone and its been up ever since. The voltage then was around the 15 - 20kV from 200 Watts of RF
On 10 March 2010 16:56, Dave Pick <[email protected]> wrote:
Stefan
Just one warning, I have used kite-supported aerials on 136 many times and you have to be careful what insulating material you have between the kite and the top of the wire. One day the kite was flying well but there was a little rain, I transmitted and the wire fell out of the sky and the kite fluttered down (fortunately I could find it!). When I looked to see what had happened the thin rope holding the wire to the kite had burned through because the rain had made it conductive. I think monofilament fishing line may be better...
Dave G3YXM
----- Original Message ----
From: Stefan Schäfer <[email protected]>
To: [email protected]
Sent: Wednesday, 10 March, 2010 12:06:06
Subject: Re: LF: KITE ANT
...In Germany you can use a maximum braid length of 100m without a special licence. If 200m would be allowed, my vertical would be a 200m ;-)
But with a special permission you can relatively easy go up to 300m! I still try to get that permission for the next weeks. Then, the VLF signal would even be more than 10dB stronger, what would give the chance for the UK to get the VLF signal, i hope so...
Static HV dangers are well known to all of us i assume. But the upper kV range is nothing mystic. 10kV is just a factor 10 of 1kV, just like 10V is a factor 10 of 1V. You can die if you touch a 10kV power line or if you touch a 100kV power line. So there is just that rule: Do not touch when under voltage and assure that there can be no voltage when you think that there is no voltage (measuring, earthing during operating). I've worked almost 6 years in the HV group of the institute of electrical energy systems (http://www.hst.tu-darmstadt.de/index.php?id=10&L=1) and had almost each week to work with voltages well above 20kV (up to 3MV, 1,2/50µs), so i think i have the necessary respect without beeing afraid or careless. On my hill there are no schools, no roads and no neighbours but i will keep in mind what you caution on! :-)
73, Stefan/DK7FC
Am 10.03.2010 09:16, schrieb [email protected]:
> Hi all
>
> May I ask you to pay some attention on the three following issues related to balloon/kite aerials ?
>
> - using "high" altitude kites or balloons is often subject to a formal authorization (at least in France, and specially if you expect to use the aerial close to an airfield)
>
> - even when weather is very good, very high DC voltages (many kV) can appear (from natural local electric field) on the antenna wire. DC grounding of the wire is therefore mandatory
>
> - avoid any AC HV lines (or schools, or roads, or irritable neighbours) in the vicinity of your experiment area.
>
> Regards
>
> Jean-Louis F6AGR
>
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