Hi Mauro,
Your shack seems to be on a high building, so a short vertical antenna
would give you better results than such a loop.
If there is no way to install a vertical, only a loop, then do it! You
will certainly make some 100 km distance with 20W!
I would use a single turn loop because the resonance curve will be very
sharp for a 2 turn loop, so the mechanical construction must be very
stable. 7m x 3m is not so bad. You may need 10 nF or so, for the
resonance (a very rough guess, without any calculations).
Instead of 6mm^2 wire i would use a RG213/RG214 cable, or many of them!
For the C is would use WIMA-FKP-1 2kV 2.2 nF types and solder a few of
them in parallel. It is most important to keep the wires as
lossless as possible, even a 1 cm piece of wire with 1mm diameter will
cause significant losses. Smaller C values could be switched in
parallel (they only have to carry a small part of the total current so
the losses are small) to find the exact resonance
Like in my images of the 1m diameter loop i would use a big ferrite
toroid to couple the TX/cable to the loop. Galvanic decoupling may be
helpful to prevent EMC problems and it is the easiest way to match the
system.
In my loop, the most lossy thing is the capacitor pack. They become
warm at > 25W.
Yes, it is a good idea to start TXing in WSPR since your signal will be
to weak for large CW distances and you will see reports giving an idea
about the signal strength and direction...
Good luck!
73, Stefan
Am 30.04.2015 23:16, schrieb IK1WVQ Mauro:
73 to all,
I would like to know your opinion about this:
I can made a square TX loop for 470KHz of 7 * 3 meters (see picture) in
the terrace of the building where I live (6 floors).
the questions are:
- it is enough a 6mmq copper electric wire ?? (20W is the output
power of my tx).
- single turn or two turns spaced 10cm max ?? (two turns = less pF
required to take the resonance).
- Is this a good idea to start to trasmit on 470KHz WSPR ??
thanks in advance for your attention.
73 de Mauro IK1WVQ
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