Thank you for your detailed explanations
I can recycle 16cm diameter PVC tube. As seen in the calculators and assuming a copper wire with plastic cover to be 3mm diameter
can wind 300 turns in 90cm lenght which would be 2.33 mH. That can be a starting point and the coil should be attached to the bottom support
of the vertical antenna. See and old picture here showing the setup
May be 5pF/m is the standard assumption for a vertical antenna against horizontal ground plane. But here the counter poise will be different
and probably showing much less capacity. I can use a high voltage capacitor in parallel with the coil to tune. The variable capacitor I'm
already using with the loop, for example. Would it make the trick to use a smaller coil ??
You can also use a spark gap in parallel to the coil. I have done the same here on my antenna
Frightening ! But if the spark is boxed into a red lantern will be also useful as visual beacon for aeroplanes :-)))
I changed the subject of the discussion.
Am 20.05.2015 14:34, schrieb VIGILANT Luis Fernández:
I don't know more than one can see on the image. My coil dimensions are not relevant for you, just the principal configuration.
Which is the turn count on your variometer ?? I can count about 10 in the internal coil but how many in the outer coil ?
You can assume to have 5 pF/m, i.e. about 55 pF for your vertical antenna. So for 475 kHz you will need L = 2.04 mH
There are many coil calculators in the web. I recommend such a simple single layer coil. No need to spend to much effort here.
Sure, at least for first experiments you can use a normal coil. You can also start with a smaller coil, maybe 10 cm diameter and enamelled cu wire. This is quickly done. But do not use ferrite or iron powder cores! It must be an air coil.
May be a variometer is not needed as I can adjust the lenght of the antenna. Althought loosing lenght (height) is never an advantage
a fixed coil would simplify the test
Reducing the antenna height is not a good idea :-)
If the building is 80m high, your 11m vertical will not make a big difference. You can also use a spark gap in parallel to the coil. I have done the same here on my antenna, see
One of the reasons to avoid using the vertical Ae hardwired to GND via coil is not to become the Franklin lighthing arrestor of the building ! :-(