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Re: LF: TXing on VLF again, Iron powder cores... broomstick coil?

To: "[email protected]" <[email protected]>
Subject: Re: LF: TXing on VLF again, Iron powder cores... broomstick coil?
From: VIGILANT Luis Fernández <[email protected]>
Date: Sun, 17 Apr 2016 15:02:58 +0000
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Thread-topic: LF: TXing on VLF again, Iron powder cores... broomstick coil?

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 which is set to maximum inductance
The total inductance L1+L2+L3 rises to 6,9mH. Then the resonance is found at 134130Hz
That gives me 204pF when calculated

Have been playing adding small ferrite inductances to see if that matches the calculations
I ended adding 5x100mH + 5x68mH + 5x47mH. A total of 1075mH plus 6,9mH of the other coils
Then found the resonance at 10800Hz. Very bad SWR, high Z and minimum bandwith 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 connecting 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 capacity

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

BTW: I'm using Shark110 for my measures and this reach down lo 10KHz. I asked in the Google forum if
there is any possibility to get it usable at 8KHz. Overnight, Melchor EA4FRB answered with an experimental
firmware version which works down to 7KHz ! :-)

73 de Luis

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 windstand almost vertical in the wind.
Is a crazy idea to run that thing in such a populated area as this. There are some flights of small planes
and helicopters at low altitude here. A good way to call for "attention". Should be limited to night time
Even then, the city lights are strong and balloon-kite would be visible. Too risky, I'm afraid ....  :(

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