Message-ID: <1688a5a4244.marcocadeddu@tin.it>
Date: Sat, 26 Jan 2019 14:29:57 +0100 (CET)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: R: LF: TXing WSPR/MF on an indoor loop
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so you are planning the old fashion indoor frame antenna ;-)
For a longer life of the caps, WIMA has detailed datasheet and you can find=
 series with specified current limits.
Also CD has caps with high current.
Remaining in argoument of small antennas wish to post the almost incredible=
 resoults of a friend of mine: he has a D2T antenna which is sold as broadb=
and antenna (in fact it is a terminated transmission line.. something like =
a folded elevated beverage ;-).
Although the very small footprint, after adding a second impedance transfor=
mer (the original one because of the core is limited to 160m), he tested D2=
T on MF and even LF. The gain (loss) of the antenna is a bit more than a du=
mmy load, but he got wspr spot from several hundred km distance!

73, Marco IK1HSS


----Messaggio originale----
Da: selberdenken@posteo.de
Data: 26-gen-2019 13.57
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: R: LF: TXing WSPR/MF on an indoor loop

Hi Paul,

Oh yes, you are right, i forgot that. In the same way they could limit=20
the maximum current at a given frequency and capacity...
But this is probably to keep a certain life time and guarantee a certain=20
deviation of the nominal capacity, for commercial applications...

I'm just thinking about a multi-turn TX loop that uses no capacitor at=20
all. Imagine a loop with say 15 turns of the same wire i am using now.=20
It will have 45 Ohm then? Now one turn results in 0.2 Ohm. When touching=20
the capaciors during the transmission, i notice they heat up by 15 =C2=B0C=
=20
maybe, not to much. So i estimate the losses are about 2 W, i.e. most of=20
the losses are in the wire. A loop of 15 turns will have an internal=20
capacity and a self resonance frequency. Maybe it can be tuned to 475=20
kHz, then you can close the loop without a serial C! and inject a RF=20
current with a ferrite core just like i do now. The residual impedance=20
will have no reactive component. And then, the limiting factor will be=20
the maximum temperature of the wire and its mechanical expansion when it=20
becomes warm, which will detune the loop like the upheating capacitor=20
does. But that time constant will be higher, so you tune it out for a=20
given average power when TXing WSPR.

73, Stefan

Am 26.01.2019 13:02, schrieb N1BUG:
> Hi Stefan,
>
> Congrats on your results with the small indoor loop!
>
>   =20
>> The limiting factor in that system is the capacitor! I use 2.2 nF +6.8
>> nF + 1090 pF variable C. Maybe it can be optimised by using 10 x 1 nF
>> WIMA-FKP-1-2000. The voltage is about 450 V, which is well below the 700
>> V limit.
>>     =20
> You may want to take a close look into the WIMA data sheet. There
> are charts showing maximum permitted Vrms vs. frequency. I think you
> may find the 1 nF 2000VDC / 700VAC FKP is derated to around 300 Vrms
> at 475 kHz. I had some experience destroying these things... :-)
>
> 73,
> Paul
>
>   =20


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so you are planning the old fashion indoor frame antenna ;-)<br>For a longe=
r life of the caps, WIMA has detailed datasheet and you can find series wit=
h specified current limits.<br>Also CD has caps with high current.<br>Remai=
ning in argoument of small antennas wish to post the almost incredible reso=
ults of a friend of mine: he has a D2T antenna which is sold as broadband a=
ntenna (in fact it is a terminated transmission line.. something like a fol=
ded elevated beverage ;-).<br>Although the very small footprint, after addi=
ng a second impedance transformer (the original one because of the core is =
limited to 160m), he tested D2T on MF and even LF. The gain (loss) of the a=
ntenna is a bit more than a dummy load, but he got wspr spot from several h=
undred km distance!<br><br>73, Marco IK1HSS<br>
<br>
----Messaggio originale----<br>Da: selberdenken@posteo.de<br>Data: 26-gen-2=
019 13.57<br>A: &lt;rsgb_lf_group@blacksheep.org&gt;<br>Ogg: Re: R: LF: TXi=
ng WSPR/MF on an indoor loop<br><br>Hi Paul,<br><br>Oh yes, you are right, =
i forgot that. In the same way they could limit <br>the maximum current at =
a given frequency and capacity...<br>But this is probably to keep a certain=
 life time and guarantee a certain <br>deviation of the nominal capacity, f=
or commercial applications...<br><br>I'm just thinking about a multi-turn T=
X loop that uses no capacitor at <br>all. Imagine a loop with say 15 turns =
of the same wire i am using now. <br>It will have 45 Ohm then? Now one turn=
 results in 0.2 Ohm. When touching <br>the capaciors during the transmissio=
n, i notice they heat up by 15 =C2=B0C <br>maybe, not to much. So i estimat=
e the losses are about 2 W, i.e. most of <br>the losses are in the wire. A =
loop of 15 turns will have an internal <br>capacity and a self resonance fr=
equency. Maybe it can be tuned to 475 <br>kHz, then you can close the loop =
without a serial C! and inject a RF <br>current with a ferrite core just li=
ke i do now. The residual impedance <br>will have no reactive component. An=
d then, the limiting factor will be <br>the maximum temperature of the wire=
 and its mechanical expansion when it <br>becomes warm, which will detune t=
he loop like the upheating capacitor <br>does. But that time constant will =
be higher, so you tune it out for a <br>given average power when TXing WSPR=
.<br><br>73, Stefan<br><br>Am 26.01.2019 13:02, schrieb N1BUG:<br>&gt; Hi S=
tefan,<br>&gt;<br>&gt; Congrats on your results with the small indoor loop!=
<br>&gt;<br>&gt;&nbsp;&nbsp;&nbsp; <br>&gt;&gt; The limiting factor in that=
 system is the capacitor! I use 2.2 nF +6.8<br>&gt;&gt; nF + 1090 pF variab=
le C. Maybe it can be optimised by using 10 x 1 nF<br>&gt;&gt; WIMA-FKP-1-2=
000. The voltage is about 450 V, which is well below the 700<br>&gt;&gt; V =
limit.<br>&gt;&gt;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <br>&gt; You may want to t=
ake a close look into the WIMA data sheet. There<br>&gt; are charts showing=
 maximum permitted Vrms vs. frequency. I think you<br>&gt; may find the 1 n=
F 2000VDC / 700VAC FKP is derated to around 300 Vrms<br>&gt; at 475 kHz. I =
had some experience destroying these things... :-)<br>&gt;<br>&gt; 73,<br>&=
gt; Paul<br>&gt;<br>&gt;&nbsp;&nbsp;&nbsp; <br><br><br><br>

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