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Date: Sun, 03 Feb 2019 14:58:04 +0100
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: LF: TXing WSPR/MF on an indoor loop, part 2
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...indeed! Since more than 72 hours i'm running the WSPR transmission in
25% duty cycle (each 8 minutes). First i tuned to 20 A antenna current
and the temperature / antenna current changes were much smaller. But
there was a certain click, or krrrrkkrt audible from the Cs. It was
likely that there were indeed internal voltage breakthroughs, which were
self-healing. Now after 3 days the current dropped again to 14 A,
meaning that the capacity dropped, so the loop became detuned and so the
RF current and voltages dropped to a level which is accepted by the
capacitors.

So my conclusion is, the derating curves actually should be considered.

I wonder if the effect is still happening if one keeps the temperatures
down at 25 C or even lower. When placing the capacitors in de-ionised
iced water, it should be possible to keep the temperatures down, also in
the internal of the capacitor.

But all in all this is not a good solution. Fortunately i have another
antenna which is more efficient :-)

73, Stefan


Am 31.01.2019 11:54, schrieb dhchurch:
> Hello Dimitrios
> Polypropylene capacitors can actually self-heal to such an extent that
> there's little left of them. The melting point of polypropylene is not
> very high and they can end up as just a liitle blob of plastic.
> Don't worry though, I still use them suitably rated for the frequency
> in use and most of them are 600Vac or more.
> 73, Hugh, M0DSZ
>
>     ----- Receiving the following content -----
>     *From:* Dimitrios Tsifakis <mailto:dtsifakis@gmail.com>
>     *Receiver:* rsgb_lf_group <mailto:rsgb_lf_group@blacksheep.org>
>     *Time:* 2019-01-31, 00:25:55
>     *Subject:* Re: LF: TXing WSPR/MF on an indoor loop, part 2
>
>     Hi Stefan,
>
>     In my experience these polypropylene capacitors when they fail, they
>     just lose some capacitance. I think they call it 'self healing', maybe
>     they imply that when they fail there is no short circuit?
>
>     I have some really nice silver mica capacitors (ex MW broadcast stuff)
>     that would be perfect for this task...
>
>     Anyway, I am slowly gearing up for some VLF action over here. The
>     other day I did some tests at 16.72 kHz into an ugly loop (very
>     roughly 120 metres by 3 metres, single turn) and I was able to receive
>     my signals using an unoptimise ferrite antenna at a bit over 2 km from
>     the TX. I don't think I am in the near field at that distance, am I?
>     :-)
>
>     73, Dimitris VK2COW
>
>     >
>

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...indeed! Since more than 72 hours i'm running the WSPR transmission
in 25% duty cycle (each 8 minutes). First i tuned to 20 A antenna
current and the temperature / antenna current changes were much
smaller. But there was a certain click, or krrrrkkrt audible from the
Cs. It was likely that there were indeed internal voltage
breakthroughs, which were self-healing. Now after 3 days the current
dropped again to 14 A, meaning that the capacity dropped, so the loop
became detuned and so the RF current and voltages dropped to a level
which is accepted by the capacitors.<br>
<br>
So my conclusion is, the derating curves actually should be considered.<br>
<br>
I wonder if the effect is still happening if one keeps the temperatures
down at 25 C or even lower. When placing the capacitors in de-ionised
iced water, it should be possible to keep the temperatures down, also
in the internal of the capacitor.<br>
<br>
But all in all this is not a good solution. Fortunately i have another
antenna which is more efficient :-)<br>
<br>
73, Stefan<br>
<br>
<br>
Am 31.01.2019 11:54, schrieb dhchurch:
<blockquote cite="mid:DM__190131105008_42113600808@smtp.eclipse.co.uk"
 type="cite">
  <title></title>
  <meta
 content="KsDHTMLEDLib.ocx, FreeWare HTML Editor 1.164.2, &copy; Kurt Senfer"
 name="GENERATOR">
  <meta http-equiv="Content-Type" content="text/html; charset=GB2312">
  <div>Hello Dimitrios</div>
  <div>&nbsp;</div>
  <div>Polypropylene capacitors can actually self-heal to such an
extent that there's little left of them. The melting point of
polypropylene is not very high&nbsp;and they can end up as just a liitle
blob of plastic.&nbsp;</div>
  <div>&nbsp;</div>
  <div>Don't worry though, I still use them suitably rated for the
frequency in use and most of them are 600Vac or more.</div>
  <div>&nbsp;</div>
  <div>73, Hugh, M0DSZ</div>
  <blockquote
 style="border-left: 2px solid rgb(0, 0, 0); padding-right: 0px; padding-left: 5px; margin-left: 5px; margin-right: 0px;">
    <div
 style="font-weight: normal; font-size: 9pt; line-height: normal; font-style: normal; font-variant: normal;">-----
Receiving the following content ----- </div>
    <div
 style="background: rgb(228, 228, 228) none repeat scroll 0% 0%; font-weight: normal; font-size: 9pt; -moz-background-clip: border; -moz-background-origin: padding; -moz-background-inline-policy: continuous; line-height: normal; font-style: normal; font-variant: normal;"><b>From:</b>
    <a moz-do-not-send="true" href="mailto:dtsifakis@gmail.com">Dimitrios
Tsifakis</a> </div>
    <div
 style="font-weight: normal; font-size: 9pt; line-height: normal; font-style: normal; font-variant: normal;"><b>Receiver:</b>
    <a moz-do-not-send="true" href="mailto:rsgb_lf_group@blacksheep.org">rsgb_lf_group</a>
    </div>
    <div
 style="font-weight: normal; font-size: 9pt; line-height: normal; font-style: normal; font-variant: normal;"><b>Time:</b>
2019-01-31, 00:25:55</div>
    <div
 style="font-weight: normal; font-size: 9pt; line-height: normal; font-style: normal; font-variant: normal;"><b>Subject:</b>
Re: LF: TXing WSPR/MF on an indoor loop, part 2</div>
    <div><br>
    </div>
    <div>
    <div>Hi Stefan,<br>
    <br>
In my experience these polypropylene capacitors when they fail, they<br>
just lose some capacitance. I think they call it 'self healing', maybe<br>
they imply that when they fail there is no short circuit?<br>
    <br>
I have some really nice silver mica capacitors (ex MW broadcast stuff)<br>
that would be perfect for this task...<br>
    <br>
Anyway, I am slowly gearing up for some VLF action over here. The<br>
other day I did some tests at 16.72 kHz into an ugly loop (very<br>
roughly 120 metres by 3 metres, single turn) and I was able to receive<br>
my signals using an unoptimise ferrite antenna at a bit over 2 km from<br>
the TX. I don't think I am in the near field at that distance, am I?<br>
:-)<br>
    <br>
73, Dimitris VK2COW<br>
    <br>
&gt;<br>
    <br>
    </div>
    </div>
  </blockquote>
</blockquote>
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