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

[DK7FC <selberdenken@posteo.de>]

Hi Luis,

Am 17.04.2016 17:02, schrieb VIGILANT Luis Fernández:

That gives me 204pF when calculated

That sounds real.

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

Oh, i see on which band you want to end :-)

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

That is the best idea if you want to get a high radiation resistance. Installing 4 towers in the corners of the building, hanging up a horizontal loop with the perimeter of the building and then using this loop as a capacitive top load for the vertical feed wire!
If you can do that, it is the best solution you can get on the roof, if a kite or a wire to the other building is not possible.

Getting down a couple of KHz there is HARD ! ........  just as Stefan explained ! :(

But I'm sure it really worth the effort

Yes. First you need a RX in your remote location, then you can start with veeeeery low power to see a faint trace on your own receiver :-)

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 ! :-)

You can use an amperemeter for 100uA and a bridge rectifier in series to the antenna to measure the current. Resonance is at the highest current.
Or, you could use a notebook with a short wire connected to the mic input, run SpecLab and slowly turn the frequency from 0...24 kHz, so you can see where the voltage across the antenna is maximum. This is resonance too...

73, Stefan