From: =?iso-8859-1?Q?VIGILANT_Luis_Fern=E1ndez?= <luis@vigilant.es>
To: "rsgb_lf_group@blacksheep.org" <rsgb_lf_group@blacksheep.org>
Thread-Topic: LF: TXing on VLF again, Iron powder cores... broomstick coil?
Thread-Index: AQHRmKDaEZrir7GFMU+s9QRoLWl1HZ+ONwfO
Date: Sun, 17 Apr 2016 15:02:58 +0000
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Subject: Re: LF: TXing on VLF again, Iron powder cores... broomstick coil?
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Hi VLF

Today I had some time to measure the coils inductance and find the antenna =
capacity value

Im already working with three coils in series. L1 contains a variometer whi=
ch is set to maximum inductance
The total inductance L1+L2+L3 rises to 6,9mH. Then the resonance is found a=
t 134130Hz
That gives me 204pF when calculated

Have been playing adding small ferrite inductances to see if that matches t=
he calculations
I ended adding 5x100mH + 5x68mH + 5x47mH. A total of 1075mH plus 6,9mH of t=
he other coils
Then found the resonance at 10800Hz. Very bad SWR, high Z and minimum bandw=
ith but the angle
of Zs can be seen chaging at this frequency. That matches the 205pF value, =
so it must be about that

As Stefan said, I would need to increase capacity. So far I'm using two 11m=
 sloppers from top of the antenna
Can extend them to about 15m leaving 5m of rope to the supporting pvc pipe.=
 Not easy to add sloppers in other
directions. They would be short and in high angle. What I can do is connect=
ing the ends of the two sloppers
forming an horizontal arc following the building perimeter. Something like =
half the horizontal loop I had last
year. Don't know if that will be a good idea or not, looking to increase ca=
pacity

Getting down a couple of KHz there is HARD ! ........  just as Stefan expla=
ined ! :(
But I'm sure it really worth the effort

BTW: I'm using Shark110 for my measures and this reach down lo 10KHz. I ask=
ed in the Google forum if
there is any possibility to get it usable at 8KHz. Overnight, Melchor EA4FR=
B answered with an experimental
firmware version which works down to 7KHz ! :-)

73 de Luis
EA5DOM

PS: I have been in the kite hobby for some years. Even know some guys which=
 manufacture something which
is a mixture of hellium zeppelin but having the kite aerodynamics to windst=
and almost vertical in the wind.
Is a crazy idea to run that thing in such a populated area as this. There a=
re some flights of small planes
and helicopters at low altitude here. A good way to call for "attention". S=
hould be limited to night time
Even then, the city lights are strong and balloon-kite would be visible. To=
o risky, I'm afraid ....  :(


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<div style=3D"direction: ltr;font-family: Tahoma;color: #000000;font-size: =
10pt;">Hi VLF
<div><br>
</div>
<div>Today I had some time to measure the coils inductance and find the ant=
enna capacity value</div>
<div><br>
</div>
<div>Im already working with three coils in series. L1 contains a variomete=
r which is set to maximum inductance</div>
<div>The total inductance L1&#43;L2&#43;L3 rises to 6,9mH. Then the resonan=
ce is found at 134130Hz</div>
<div>That gives me 204pF when calculated</div>
<div><br>
</div>
<div>Have been playing adding small ferrite inductances to see if that matc=
hes the calculations</div>
<div>I ended adding 5x100mH &#43; 5x68mH &#43; 5x47mH. A total of 1075mH pl=
us 6,9mH of the other coils</div>
<div>Then found the resonance at 10800Hz. Very bad SWR, high Z and minimum =
bandwith but the angle</div>
<div>of Zs can be seen chaging at this frequency. That matches the 205pF va=
lue, so it must be about that</div>
<div><br>
</div>
<div>As Stefan said, I would need to increase capacity. So far I'm using tw=
o 11m sloppers from top of the antenna</div>
<div>Can extend them to about 15m leaving 5m of rope to the supporting pvc =
pipe. Not easy to add sloppers in other</div>
<div>directions. They would be short and in high angle. What I can do is co=
nnecting the ends of the two sloppers&nbsp;</div>
<div>forming an horizontal arc following the building perimeter. Something =
like half the horizontal loop I had last</div>
<div>year. Don't know if that will be a good idea or not, looking to increa=
se capacity</div>
<div><br>
</div>
<div>Getting down a couple of KHz there is HARD ! ........ &nbsp;just as St=
efan explained ! :(</div>
<div>But I'm sure it really worth the effort</div>
<div><br>
</div>
<div>BTW: I'm using Shark110 for my measures and this reach down lo 10KHz. =
I asked in the Google forum if</div>
<div>there is any possibility to get it usable at 8KHz. Overnight, Melchor =
EA4FRB answered with an experimental</div>
<div>firmware version which works down to 7KHz ! :-)</div>
<div><br>
</div>
<div>73 de Luis</div>
<div>EA5DOM</div>
<div><br>
</div>
<div>PS: I have been in the kite hobby for some years. Even know some guys =
which manufacture something which</div>
<div>is a mixture of hellium zeppelin but having the kite aerodynamics to w=
indstand almost vertical in the wind.</div>
<div>Is a crazy idea to run that thing in such a populated area as this. Th=
ere are some flights of small planes</div>
<div>and helicopters at low altitude here. A good way to call for &quot;att=
ention&quot;. Should be limited to night time</div>
<div>Even then, the city lights are strong and balloon-kite would be visibl=
e. Too risky, I'm afraid .... &nbsp;:(</div>
<div><br>
</div>
<div>
<div style=3D"font-family: Times New Roman; color: #000000; font-size: 16px=
">
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