Hi Rik, my take on the elevated coil effect, when there is lossy envoroment
around goes like this.......
The loss to the environment of the vertical section can be modeled as a
lossy capacitor to ground, connected just above the loading coil. The
current flowing into the loss is dependent on the size of the capacitor AND
the RF voltage at that point. When you elevate the coil (or part of it) you
reduce the voltage on that part of the antenna, so much less current flows
into the loss. I like to think of this loss current being "diverted" before
it can flow through the "radiation resistance" and add to the ERP. It may be
a bit naive but it convinces me :-))
Best Wishes
Alan G3NYK
----- Original Message -----
From: "Rik Strobbe" <[email protected]>
To: <[email protected]>
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
________________________________
Van: [email protected] [[email protected]]
namens Paul A. Cianciolo [[email protected]]
Verzonden: maandag 5 april 2010 16:31
Aan: [email protected]
Onderwerp: LF: RE: RE: RE: W1VLF 9 Khz Antenna update Putting inductance
near the top.
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
-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Rik Strobbe
Sent: Sunday, April 04, 2010 5:40 PM
To: [email protected]
Subject: LF: RE: RE: W1VLF 9 Khz Antenna update Putting inductance near the
top.
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
________________________________
Van: [email protected] [[email protected]]
namens Paul A. Cianciolo [[email protected]]
Verzonden: zondag 4 april 2010 22:28
Aan: [email protected]
Onderwerp: LF: RE: W1VLF 9 Khz Antenna update Putting inductance near the
top.
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
-----Original Message-----
From: Stefan Schäfer [mailto:[email protected]]On Behalf Of
Stefan Schäfer
Sent: Sunday, April 04, 2010 12:49 PM
To: [email protected]
Subject: AW: W1VLF 9 Khz Antenna update
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
________________________________
Von: [email protected] im Auftrag von Paul A. Cianciolo
Gesendet: So 04.04.2010 17:18
An: [email protected]
Betreff: LF: W1VLF 9 Khz Antenna update
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
-----Original Message-----
From: Stefan Schäfer [mailto:[email protected]]On Behalf Of
Stefan Schäfer
Sent: Sunday, April 04, 2010 7:44 AM
To: [email protected]
Subject: AW: Activity 3 Mar 2010
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
________________________________
Von: [email protected] im Auftrag von Mike Dennison
Gesendet: So 04.04.2010 12:09
An: [email protected]
Betreff: LF: Activity 3 Mar 2010
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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