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Rik,
Yes , I added a coil to the top
of the vertical section of my inverted, L and that improved
performance on 500k as well as 1.8 / 3.8 Mhz , 40 turns on a 4
inch former , still there now ,originally with
2 x 40ft x 5 ft separated capacity wires , however
the wind snapped one of the capacity
wires connected to the coil and changed the top into 80
feet of wire in a 5 ft separated U section and the gain
increased slightly ..so it look's like the top is acting
'just' as a capacity section , Ae is end fed against earth by
variometer and auto transformer for 500 and a
conventional atu for hf , earth is everything that conducts in
the back garden !
73 - G ..
Sent: Monday, April 05, 2010 4:17 PM
Subject: LF: RE: RE: RE: RE: W1VLF 9 Khz Antenna update Putting
inductance near the top.
Paul,
if you put the coil at the top
of a tower try to keep it as far as possible from metal object as these can
lower the Q.
About the "working
principle":
a coil at the top of the vertical section
will reduce the "current deflation" through the vertical section. The
result is a higher average current and thus a larger radiation resistance (or
effective height if you prefer that).
The stange thing is that the improvement
measured is (much) more than the theoretical value if the antenna is surrounded
by trees, buidings etc...
In my 136kHz antenna setup the theoretical
gain was about 1dB, while 5dB was measured by PA0SE.
I did construct a light weight coil that
was just "hanging" at the top of the vertical section, far away from any lossy
objects. So I am not sure what the effect will be if the coil is close to metel
or wet wood.
I guess the only way to find out is to try
...
73, Rik ON7YD - OR7T
Rik
Thanks for that
reply. Very interesting material.
I am going to
attempt to put a coil at the top about 1 meter below where the top hat
begins.
The value will be
approx 1/2 of the overall value needed to resonate.
The QTH is hardly
the best site for LF VLF so perhaps it
will help.
Later I take
pictures of my QTH and put them on the web, someone suggested that a while
ago.
This would give
others the ability to "Critique" the antenna.
I still do not
really understand the premise by which coil works to increase
gain.
PauLC
W1VLF
Hello Paul,
after I published my experiences several
hams tried elevated loading coils on 137kHz.
Significant improvement was
observed when the antenna was surrounded by high obstacles (trees, buildings),
when the antenna was "free" there was little or no gain.
I have no idea what the effect will be
on 9kHz, but if you can install an elevated loading coil it whitout too
much effort I would suggest to try it.
In my case most stations noticed a
signal increase of about 1 S point and PA0SE measured the field strength and
noticed a difference of 5dB.
73, Rik ON7YD - OR7T
Stefan
On page 60 and
61 of the Low Frequency Experimenters Handbook Peter Dodd RSGB there is
an example putting a coil near the top of the antenna
In this case
the transmitter is on 137 Khz and a of a portion (1/2) of the "L" needed to
resonate was moved near the top. According to measurements by Rik Strobbe
ON7YD an increase of 4 to 5 db was measured.
Do you think it
would be worth the effort to put 1/4 of the total "L" needed near the
top
I could do that
very easily.
PaulC
W1VLF
Hello Paul,
This sounds really improving!! And this
will give a much more efficient antenna as before. Also the HV problems will
be reduced. Note that the goal should not be to make the C as high as
possible but first to make the antenna efficiency as high as possible. This
is done be increasing the effective height and reducing all the losses. Thus
i would recommend now a combination out of option 2 and 3. Maybe you could
check with G3YNKs R-C bridge, if the losses are increased with option 3. You
could use a braid of some meters to keep a distance to the trees although
the wire is mounted on the trees.
But all in all it sounds very
promising!
Option 1 is not so much improving i
would say. The C would slightly increase but not the antenna efficiency i
mean...
What about the option to place the coil
on the 40m tower? That would be the best improvement you can
do!
Good luck!
Do you already know who could be the
next receiving ham station? ;-)
73, Stefan/DK7FC
Stefan,Group.
An update on
the W1VLF hopefully to be 9 KHZ antenna.
The 55 meter
wire sloping at 45 degrees measured 340 pf as you
recall.
The addition
of 2 top hat wires has been made, each over 50 meters long with a slope to
the ground.
Wire 1 is
terminates at 11 meters above the ground and wire 2 terminates 20 meters
above the ground.
Antenna _only_
= 340 pf
Antenna
and Wire 1 West = 650 pf
Antenna
and wire 1 West and wire 2 East = 900
pf
L to resonate
at 9 KHZ now = 350 mHy.
The L is now
coming down to a reasonable size!!
For the
next step there are 3 possibilities:
1) Change the
top 30 meters from a single wire, to 3 wires spread 1 meter apart at
the top to gain perhaps 100 more PF?
2) Get my
neighbors permission to use his tree as a support for the end rope on wire
1. This will increase wire 1 west about 40 meters and raise the
end from 10 meters to 20 meters. 200 PF more?
3) Run 2 more
wires Wire 3 Northwest and Wire 4 Northeast each would be 20 to
30 meters long and terminate at 30 meters high. These would be
over a forest and I am not sure if this is my best
option.
It may yield
more "C" and lot more losses??
Goal is to
try to get antenna "C" to 1200 pf or more
All ideas
welcome.
PauLC
W1VLF
Mike, LF,
Wow! 5641km is really impressing!
Congrats!!
Is there such an activity planned for
the "west-stations" as well? We could do the same!
I've never been slower than DFCW-10
on LF. Would be interesting :-)
73, Stefan/DK7FC
An excellent day's activity on 137kHz yesterday with 5
countries
received, the furthest easterly station received here and a
QSO with
a new country.
In the morining, OE5ODL and DJ6GT were
received.
During the UA tests, five stations were logged (see the
attached
screen grab - Argo set to QRSS30 and centred on
137.778kHz).
The picture shows (from the top) UA0AET (5641km from me);
RA3YO;
RN3AGC; UA4WPF; and EW6GB who was first received as early as
1700UTC.
After the formal test I exchanged 'O' reports with EW6GB
at 1902km,
using QRSS10.
Well done to all
concerned.
Mike,
G3XDV
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