Hi MF,
I've played a bit arround with my 1m diameter loop (copper, 18mm
diameter x 1mm). Last year i used it as a receive loop. Today i asked
myselfe what distance could be made with such a loop when transmitting
on MF WSPR, indoors!
For LF i needed 501 nF to resonate it to 137 kHz and a ferrite core with
the primary turn across the capacitor. Primary way 29 turns and
secondary (matched to 50 Ohm!) was 10 turns.
Now for MF i just need 40.5 nF to resonate it to 475.7 kHz and a ferrite
transformer arround the copper tube (=1 turn primary) and 35 turns on
the transmitter side to match it to about 50 Ohm.
Photos:
https://dl.dropboxusercontent.com/u/19882028/MF/MF%20TX%20loop%20all.jpg and
https://dl.dropboxusercontent.com/u/19882028/MF/MF%20TX%20loop%20zoom.jpg
I thought this way (tube through the ferrite transformer, i.e. a single
turn on one side) is better because here, when TXing, the voltage across
the C will be very high and will be the limiting factor for the system.
Later i found that it actually is the current which warms up the
capacitors. The voltage in a steady state is just about 300 V rms. So
the antenna current must be 36 A. In that case, the TX power is in the
range of 30W, so it's quite QRP (for me) :-)
Of course i do not expect much. Any detection in WSPR-2 outside the near
field will make me happy for this test.
So, while TXing WSPR-15 on LF here at work this night, i will carry the
antenna and my small PA + equipment to my home QTH in JN49IJ, which is a
distance of 0.95 km, even more than 1 Lambda ;-) Depending on the
results i will TX through the night, beaming to NW/SE (G, PA) or WSW/NNE
(F).
Reports apprechiated!
73, Stefan/DK7FC
PS: This is the fun of practical amateur radio work: I'm looking forward
to the results and still don't know them. Some others would read some
papers, calculate the ERP , estimate the distance and then go back to TV :-)
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