Mal,
No.
It depends on the frequency. On 8970 Hz and lower it is an earth
antenna.
Mal, it was so often explained how an earth antenna works. Do we really
have to repeat that each few weeks? Really? OK, once again:
And earth electrode antenna is a loop antenna where the current return
path is in the earth. So there are two electrodes and the TX can be
applied anywhere between these two electrodes. Furthermore i have never
said to have 2 wires (600m each) but just one wire. The TX ground is
connected to the first (near) ground rod(s) and the center of the coax
is applied to the wire which is in 6m height (average). The total wire
length is about 700m and the electrode spacing is about 600m. So the
far away electrode is in 600m distance.
Rogers and my earth antenna is not a grounded loop antenna since the
wire is not closed! The ground is a part of the loop, thats the
difference between a usual loop and an earth antenna.
I can run a current at any frequency. I have tried 10 Hz (just for
testing) and DC and 100 Hz and so on. I hope you can agree that the
current MUST come back trough the ground if the frequency is 0 (DC)!!
So, the lower the conductivity, the higher the effective area of the
loop (skin effect!!!) and thus the efficiency. Since i am on a hill
there (500m ASL) and there are almost only stones, the conductivity is
very low. This causes more effort in arranging a suitable earth rod
system ( i am using 30 rods, 0.4m long each, spaced about 1m) but is is
interesting :-)
There is no matching from 8 Ohm to 50 Ohm since my PA has not an output
impedance of 8 Ohm and my antenna has not an input impedance of 50 Ohm
;-)
The goal is to get as much antenna current as possible, so there is no
need to match something to 50 Ohm. Since the cable length is always
<<< Lambda, there is no need to match something! I can measure
the antenna current directly by using a digital multimeter(attached
picture). The power can be measured on the DC side of the PA, since the
efficiency is quasi 100%. So you can calculate the losses.
If the earth antenna has a overall resistance of 500 Ohm and you can
and want to generate 500 W (assuming the reactive Z component is
negligible) you just have to apply 500 V (rms) on the wire, thats all!
Earth antenna does not mean that the wire is on the ground but that the
current comes back in the earth!
So, hope to have answered the questions, in december.
73, Stefan
Am 14.12.2010 20:52, schrieb mal hamilton:
Stefan
You now admit that your antenna is
in FACT a LOSSY DIPOLE and not an earth antenna
g3kev
-----
Original Message -----
Sent:
Tuesday, December 14, 2010 6:12 PM
Subject:
Re: LF: Earth Electrodes
Chris, LF,
Am 14.12.2010 17:27, schrieb Chris:
HiStefan,
Yes, but 600m is VERY long! The
wire even laying on the ground I would expect to radiate quite well at
137 with that length! And how many watts?? ERP??
I am sure 8970 would do well through
the ground at the sort of powers being spoken about. Probably
ideal for submarines, as Roger says!
Vy 73, Chris, G4AYT.
Well, my earth antenna is grounded at the ends and TX power was about
250 W. The mode was DFCW-600. The receiver was at Michael Oexner using
a PA0RDT design. ERP? No idea, probably some few uW. Its not so easy to
calculate the losses.
Yes, on 137 kHz the wire length comes close to lambda/4 and above so it
acts not just like a pure earth antenna but rather as a combination of
this and a very loss dipole. On 137, my power was 100 W at this test.
The antenna was built to do local tests but seems to work suitable on
137. So it is a fixed antenna, my only fixed one. And it is a very
quiet location. This makes it interesting to use it as a RX antenna
too!...
73, Stefan
-----
Original Message -----
Sent:
Tuesday, December 14, 2010 2:49 PM
Subject:
Re: LF: Earth Electrodes
Hi Chris,
But how do you explain that i have crossed 49.6 km with a 600m spaced
earth electrode antenna on 8970 Hz? It was rather summer time than
winther (regarding QRN)! With the same antenna, my 137 kHz signal was
seen 20 dB above noise near Paris in DFCW-3!?????
73, Stefan
Am 14.12.2010 15:15, schrieb Chris:
Hi Mal,
Yes, that is what I had
concluded years ago. No harm in trying though!
Further to your previous
e-mail to LF, looks to me like beacons are now becoming the norm on
136/7kHz band and below. I have no problem with that personally,
indeed, I think it preferable to a QSO taking forever! I woud like to
see full idents though, no matter how slow.
Vy 73,
Chris, G4AYT.
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