Message-ID: <168d6970d7b.marcocadeddu@tin.it>
Date: Sun, 10 Feb 2019 09:47:30 +0100 (CET)
From: "marcocadeddu@tin.it" <marcocadeddu@tin.it>
To:  <rsgb_lf_group@blacksheep.org>
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Subject: R: Re: VLF: in VK?
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Compliments for the new success you achieved Dimitris :-)))

I'm not an expert of VLF thus my opinion could very wrong..
1) if the caps exhibit a series resistance of 6 ohms at 2 Amperes (RF? it is almost DC hihi) they have to dissipate about 25W so they have all the rights to be warm! You should try to add more caps in parallel (if they are not tuning the antenna) or serie /parallel if they tune the antenna in order to reduce the resistance and improve the current capability.
2) how long is the coax from TX to antenna? it is probably a very small fraction of wavelenght so its mismatch should be negligible. Of course if there are problems in the connections or the material used for cable manifacture this is an ohmic matter as you pointed out ;-). Be careful low loss speaker cable are veeeeery expensive even when they are not really made of Litz wire ....
You coud do your own coax in BC style with standard power cord and spacers ;-)

73, Marco IK1HSS 


----Messaggio originale----
Da: dtsifakis@gmail.com
Data: 9-feb-2019 23.58
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: VLF: in VK?

> Not stellar SNR but the radiated power I reported originally (7.5 uW)
> is not correct. I think the capacitors have sustained some damage
> because they seem to introduce a series R of about 6 ohm! After I
> adjusted for that extra R, I now think that my radiated power was
> closer to 2.3 uW. No wonder they got hot, poor things!! So if I fix
> that problem I will gain another ~ 5dB for the same amplifier power.

Well, what do you know! The unexpected losses are not just the
capacitors (their contribution is probably small). It is also the
coaxial cable that I used between the antenna feedpoint and the
amplifier. One of the cables uses copper plated steel as the inner
core (which of course has a plating depth appropriate for the expected
skin effect at the _intended_ frequency of operation), the other has
copper plated aluminium (I think!). Even the jumper leads I used have
losses and it all adds up. I now appreciate the problem of using a
very low impedance antenna! Perhaps I should install another
transmission line from the inside of the house to the antenna but not
like the others, I should get the thickest speaker cable I can find
and use that :-)

73, Dimitris VK2COW


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Compliments for the new success you achieved Dimitris :-)))<br><br>I'm not =
an expert of VLF thus my opinion could very wrong..<br>1) if the caps exhib=
it a series resistance of 6 ohms at 2 Amperes (RF? it is almost DC hihi) th=
ey have to dissipate about 25W so they have all the rights to be warm! You =
should try to add more caps in parallel (if they are not tuning the antenna=
) or serie /parallel if they tune the antenna in order to reduce the resist=
ance and improve the current capability.<br>2) how long is the coax from TX=
 to antenna? it is probably a very small fraction of wavelenght so its mism=
atch should be negligible. Of course if there are problems in the connectio=
ns or the material used for cable manifacture this is an ohmic matter as yo=
u pointed out ;-). Be careful low loss speaker cable are veeeeery expensive=
 even when they are not really made of Litz wire ....<br>You coud do your o=
wn coax in BC style with standard power cord and spacers ;-)<br><br>73, Mar=
co IK1HSS <br>
<br>
----Messaggio originale----<br>Da: dtsifakis@gmail.com<br>Data: 9-feb-2019 =
23.58<br>A: &lt;rsgb_lf_group@blacksheep.org&gt;<br>Ogg: Re: VLF: in VK?<br=
><br>&gt; Not stellar SNR but the radiated power I reported originally (7.5=
 uW)<br>&gt; is not correct. I think the capacitors have sustained some dam=
age<br>&gt; because they seem to introduce a series R of about 6 ohm! After=
 I<br>&gt; adjusted for that extra R, I now think that my radiated power wa=
s<br>&gt; closer to 2.3 uW. No wonder they got hot, poor things!! So if I f=
ix<br>&gt; that problem I will gain another ~ 5dB for the same amplifier po=
wer.<br><br>Well, what do you know! The unexpected losses are not just the<=
br>capacitors (their contribution is probably small). It is also the<br>coa=
xial cable that I used between the antenna feedpoint and the<br>amplifier. =
One of the cables uses copper plated steel as the inner<br>core (which of c=
ourse has a plating depth appropriate for the expected<br>skin effect at th=
e _intended_ frequency of operation), the other has<br>copper plated alumin=
ium (I think!). Even the jumper leads I used have<br>losses and it all adds=
 up. I now appreciate the problem of using a<br>very low impedance antenna!=
 Perhaps I should install another<br>transmission line from the inside of t=
he house to the antenna but not<br>like the others, I should get the thicke=
st speaker cable I can find<br>and use that :-)<br><br>73, Dimitris VK2COW<=
br><br><br><br>

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