R: Re: R: LF: Antenna environment changes

["marcocadeddu@tin.it" <marcocadeddu@tin.it>]

Hi Paul, Rik and all LF/MF fellows,

let me cite another phrase: "the grass is always greener on the other side" ;-)

I'm one of those fortunate with low loss environment because my antennas are placed on the roof of the building and the roof is made of metal/foam panels that after some work is now an elevated ground (700 sqm @ 35 m) for my LF/MF Marconi type antenna.

Because of the good ground I have at resonance low impedance values mainly due to ground and coils losses (few tens of ohms depending on the frequency) but..

The radiator high is small thus the radiation resistance therefore I can reach 1W EIRP with easy on 470kHz (lesse than 200Wout) on 137kHz need approx 2kW and I've seen the effect of less than 1kW...

So never mind and enjoy the reports from Rik despite the moving antenna environment ;-)

73, Marco IK1HSS

----Messaggio originale----
Da: paul@n1bug.com
Data: 6-set-2018 12.06
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: R: LF: Antenna environment changes

Hi Rik,

I'm sorry you have such high losses but it is good to hear finally
that I am not the only one. I think sometimes people don't believe
me when I tell them I must run a few hundred watts on 137 kHz to
make 1 watt EIRP! It seems many are able to achieve loss around 10
to 50 ohms at 137 kHz. Hmm, not here...

Yes, we had our QSO despite some bad luck! :-) The nights which were
seriously tried for trans-Atlantic QSOs did not seem to be among the
best of propagation.

73,
Paul



On 09/05/2018 06:22 AM, Rik Strobbe wrote:
> Hi Paul,
> 
> same here, losses are high in summer: up to 70 Ohm (475 kHz) or
> 180 Ohm (137 kHz). In winter it drops to 35 Ohm (475 kHz) and 120
> Ohm (137kHz). I always assumed it was not so much affected the
> soil but rather by all the trees surrounding the antenna that
> loose their leaves and go to "sleep" in winter. Last february I
> raised the antenna from 12m to 14m in my attempt to get some
> extra ERP to cross the Atlantic and actually the losses increased
> slightly. I thought this was caused by the topload coming closer
> to some branches. But fortunately the overall effect was positive
> and we had our QSO ;-)
> 
> 73, Rik  ON7YD - OR7T
> 
> ________________________________________ Van:
> owner-rsgb_lf_group@blacksheep.org
> <owner-rsgb_lf_group@blacksheep.org> namens N1BUG
> <paul@n1bug.com> Verzonden: woensdag 5 september 2018 11:06 Aan:
> rsgb_lf_group@blacksheep.org Onderwerp: Re: R: LF: Antenna
> environment changes
> 
> Marco,
> 
> ... a wingbeat of a butterfly... is very descriptive. I like it.
> :) Maybe with a sensitive detector I can use the LF antenna to
> count birds flying under it. :)
> 
> Stefan,
> 
> I have not seen any significant change in loss resistance during
> the summer. Rain, dry... hot, less hot... grass mowed or not
> mowed seem to have not much influence. My loss resistance in
> summer is very high. I need that aluminum foil!
> 
> During the winter my loss resistance changed a lot with
> temperature. Colder = lower resistance. I did not understand what
> was changing. I do not think variations in temperature could
> affect the ground very much with 1m of snow over it but maybe I
> am wrong. Perhaps it was the snow itself changing with
> temperature, or maybe it was the nearby trees.
> 
> 73, Paul
> 
> 
> On 09/05/2018 04:23 AM, DK7FC wrote:
>> Paul,
>> 
>> did the LF loss resistance drop after mowing the grass? Someone
>> should try to roll out household aluminium foil completely 
>> within a radius of the height of the antenna to see how it
>> loweres the losses :-) Not so expensive actually.
>> 
>> 73, Stefan
>> 
>> Am 05.09.2018 09:56, schrieb marcocadeddu@tin.it:
>>> .. a wingbeat of a butterfly..
>>> 
>>> be careful to move around the antenna and touch metal parts
>>> while transmitting Paul it is a very "reactive" area not only
>>> for the field strenght concept :-)) I guess that the pipe
>>> laying on the ground it is part of the ground itself (maybe
>>> improving it ) when you rise it from ground level and 
>>> eventually connect to other existing metal parts you really
>>> make change in the environment of the antenna (it is like to
>>> tophat wires moving in the space when wind blows)
>>> 
>>> 73, Marco IK1HSS
>>> 
>>> ----Messaggio originale---- Da: paul@n1bug.com Data:
>>> 5-set-2018 1.09 A:
>>> "rsgb_lf_group@blacksheep.org"<rsgb_lf_group@blacksheep.org>,
>>>
>>> 
"rsgb_lf_group@yahoogroups.co.uk"<rsgb_lf_group@yahoogroups.co.uk>,
>>> "Discussion of the Lowfer (US, European, & UK) and MedFer 
>>> bands"<lowfer@mailman.qth.net> Ogg: LF: Antenna environment
>>> changes
>>> 
>>> Subtitle: Be careful what you do in the vicinity of your LF
>>> antennas...
>>> 
>>> I had a 14m length of aluminum tube (proposed 30 meter
>>> rotatable dipole) laying on the ground just under one end of
>>> the top hat of the LF antenna. Today I picked it up and moved
>>> it about 20 meters away. To get it off the ground for mowing,
>>> I ran it through the lattice of a short tower (9m) that is
>>> not at all under the LF top hat. I placed it about 2m above
>>> ground. This caused the LF antenna resonance to change so
>>> much I could not retune with the variometer! It was quite a
>>> large shift in resonant frequency.
>>> 
>>> I then experimented with moving the piece of aluminum tube
>>> around. It seems I can lay it on the ground anywhere I want
>>> with no affect to the LF antenna. But put it one or two
>>> meters above ground connected to another tower or mast and
>>> the LF antenna is drastically changed.
>>> 
>>> I must remember not to move any pieces of metal around while
>>> the beacon is active! :-)
>>> 
>>> Paul