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Try 2 turns on the loop ... !
Sent: Saturday, November 16, 2013 10:58 PM
Subject: Re: LF: RE: A /p 630m transmit loop (?)
Hi all,
Wonderful. I really didn't expect such results
from a 1m diameter indoor TX loop.!
So far (best reports):
| Timestamp |
Call |
MHz |
SNR |
Drift |
Grid |
Pwr |
Reporter |
RGrid |
km |
az |
| 2013-11-16 22:14 |
DK7FC |
0.475683 |
-27 |
0 |
JN49ik |
1 |
PA0A |
JO33de |
449 |
339 |
| 2013-11-16 20:20 |
DK7FC |
0.475679 |
-28 |
0 |
JN49ik |
1 |
PA3FNY |
JO22nc |
389 |
321 |
| 2013-11-16 20:32 |
DK7FC |
0.475685 |
-29 |
0 |
JN49ik |
1 |
PI4THT |
JO32kf |
336 |
338 |
| 2013-11-16 22:26 |
DK7FC |
0.475683 |
-19 |
0 |
JN49ik |
1 |
DL4RAJ |
JN68kj |
326 |
109 |
| 2013-11-16 20:34 |
DK7FC |
0.475684 |
-25 |
0 |
JN49ik |
1 |
DL1DBC |
JO41bi |
217 |
349 |
| 2013-11-16 21:10 |
DK7FC |
0.475682 |
-17 |
0 |
JN49ik |
1 |
DF8UO |
JN48ex |
56 |
206 |
| 2013-11-16 20:40 |
DK7FC |
0.475690 |
-26 |
0 |
JN49ik |
1 |
DK6UG |
JN49cm |
37 |
285 |
Thanks to the
reporters.
The PA consumes about 2A at 13.8V. The capacitors are warm and
were drifting until there was a steady state of temperature and antenna current.
They are abouut 20 C above the ambient temperature. These losses must come
mostly from their legs (no snubber caps). It could be useful to remove the 22nF
caps and only use 6.8 nF caps so the current is spread and the losses fall a bit
more, until i reach the voltage limit of the caps which means another 6 dB of
signal... Will see...
Now i turned the loop a bit more to NNE,
pointing to DL-SWL. But i assume he has a directional antenna pointing to the
US...
73, Stefan/DK7FC
Am 16.11.2013 20:50, schrieb Dave
G3WCB.:
Stefan,
I think that G4KPX was using a 1m indoor loop at one time. I'm copying him
right now on WSPR, but I don't know if he is still using the loop, or
something different.
Quote from an e-mail on 13th Jan by G3XBM below:-
"Another local G4KPX is using 1W RF into a 1m diameter loop indoors and
getting reports from decent distances. He is a good signal with me. Amazing.
His ERP is a lot less than 100uW."
73, Dave G3WCB IO91RM
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Stefan Schäfer
Sent: 16 November 2013 19:35
To: [email protected]
Subject: LF: A /p 630m transmit loop (?)
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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