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Message-ID: <5287C8E9.6040102@iup.uni-heidelberg.de>
Date: Sat, 16 Nov 2013 20:35:05 +0100
From: =?ISO-8859-15?Q?Stefan_Sch=E4fer?= <Stefan.Schaefer@iup.uni-heidelberg.de>
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To: rsgb_lf_group@blacksheep.org
Subject: LF: A /p 630m transmit loop (?)
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Status: O

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 :-)