Hi Rik,
I think on VLF it could be even useful to place the L as high as possible when there is "nothing" lossy in the near surrounding. I think the difference to LF is, that the coil losses on VLF can be some 100 Ohms. If
the "lost" capacitive current, that comes out of the lower part of the vertical section comes back to the coil without crossing too much earth resistance (due to the short way back to the coil) and if the coil losses are low (on LF often in the near of 10
Ohm), there is not much lost and it behaves almost as a fixed parallel C (assembly part). Thus the benefit is rather small.
On VLF, the same equivalent capacitance causes much more losses due to the higher coil resistance. The Xc is higher but U also.
I have not practically proven that and maybe the effort is not worth, don't know.
Sometimes it is better just to generate some 10W more power than installing a structure that will break down in the next storm ;-)
73, Stefan/DK7FC
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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