From: g4gvw <g4gvw@aol.com>
To: rsgb_lf_group@blacksheep.org
In-Reply-To: <38A51B74B884D74083D7950AD0DD85E82A1AEE@File-Server-HST.hst.e-technik.tu-darmstadt.de>
References: <BDEMKFCNLMIILGIFNONNIEIDDHAA.victor13@online.nl>
	 <38A51B74B884D74083D7950AD0DD85E82A1AEE@File-Server-HST.hst.e-technik.tu-darmstadt.de>
Date: Sat, 06 Feb 2010 23:45:23 +0000
Message-Id: <1265499924.4877.10.camel@pat-compaq-evo>
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Subject: Re: LF: AW: RE: active ant on metallic mast
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Hi All,

I have not been following this particularly well but would like offer
another alternative approach. With the plethora of low-cost offerings in
the 2.4Ghz and other "free" bands how about a low-power battery operated
RF link as a means of decoupling the antenna from a supporting structure
or cable. Such a device might be Solar charged during the daylight hours
and continuously transmit the signal from the antenna(e) to a suitable
Rx over a considerable distance given suitable link antenna arrangments.
This obviates the necessity to provide a physical path for an optic or
other transmission line and has the elegance of being "radio" at
frequencies in "our" part of the electromagnetic spectrum. My apologies
if someone has already suggested this - it does seem kinda obvious from
the bit of the wall that I'm coming off!

On Sat, 2010-02-06 at 23:50 +0100, Stefan Sch=C3=A4fer wrote:
> Hi Victor,=20
> =20
> Where can i get the design of your preamp? Is it a broad band design or=
 also with some band pass filters? Is it with FETs and/or with OP amps? 28=
V? I assume +-14V, right? ;-)
> Is in this shed a 230V supply or is it completely ("electrically") apart=
 from the house?
> =20
> "Less qrm and higher output", does this mean the noise level itself decr=
eased, so not compared to the wanted signal? If hight increases and the in=
fluence of surrounding lossy things decreases, the E-Field and thus the in=
put voltage increases, and thus the SNR, if noise level remains the same.=
 And if you then decrease the AF of your RX to get again a proper visible=
 signal in e.g. Argo, the noise gets into the background. But does the noi=
selevel itself decreases also significantly? If so, there must be a noise=
 source in the near of the shed, isn't it?
> =20
> I think when i will do the test with the active antenna with the 2 UKW=
 variable antennas, i will mount it to the kite and look how it depends wh=
en it is 50m above ground, completely isolated. Perhaps not very useful bu=
t interesting ;-)
> =20
> You decreased the lenght from 1m to 60cm. Have you also tried 30cm?
> A hight of 7m gave the best results you said. So things get worse, when=
 you go to 10m hight?? If so, what do you think is the reason for that? Or=
 is the shed under a 400kV power line? ;-)
> =20
> Victor and Roelof, tnx for your hints and ideas. I like that conversatio=
n and i like to try mni unusual things. A receiving loop will give the bes=
t signal i assume, but it is not very easy to handle if one is always /p.=
=20
> =20
> Congrats to the canadian stns to be back on LF!! Hpe to get a contact to=
 VO1NA next! But since 6 weeks there is almost no wind at weekend, the lon=
gest break since 2 years :-( But i will be back with a big signal :-)
> =20
> 73, Stefan/DK7FC
> =20
>=20
>=20
> ________________________________
>=20
> Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von victor13@online.n=
l
> Gesendet: Sa 06.02.2010 20:46
> An: rsgb_lf_group@blacksheep.org
> Betreff: LF: RE: active ant on metallic mast
>=20
>=20
> Hello Stefan,Roelof,
> =20
> for about 4 years now I am using an active whip with good results.The an=
tenna is placed on a shed about 10 m from the house.I varied the height be=
tween 2 m and 9 m.With a height of 2 m(the roof) I had alot of qrm and a=
 low output,raising it to 5m or higher improved things a lot.Less qrm and=
 higher output,to prevent im i decreased the size of the whip from 1m to=
 60 cm.At a height of 7m this gives the besr results.no detectable im from=
 local mw stations and a good S/N ratio of weak signals.As an experiment=
 I replaced the steel pole for a glassfibre one,this didn't change any thi=
ng.This could be espected because of the coax cable you are always at the=
 same potential as with a steel pole.Ofcourse  using a battery and a glass=
fibre changes things but for me this is not very practical because my whip=
 draws 120mA @ 28V.
> Hope to hear more from your experiments,
> =20
> 73
> Victor
> PA3FNY
>=20
>     -----Oorspronkelijk bericht-----
>     Van: Stefan Sch=C3=A4fer [mailto:owner-rsgb_lf_group@blacksheep.org]=
Namens Stefan Sch=C3=A4fer
>     Verzonden: zaterdag 6 februari 2010 17:47
>     Aan: rsgb_lf_group@blacksheep.org
>     Onderwerp: LF: active ant on metallic mast
>    =20
>    =20
>     Hi Roelof, LF,
>     =20
>     Roelof, why do you think that this is the case? Interesting Question=
! "Won't work" means "Won't work properly" it assume. There will be a sign=
al but perhaps it is not optimal. And why could this be the case? If the=
 application is in a metallic housing that is mounted to a metallic mast,=
 the capacity of the "ground electrode" against the environment must be ve=
ry high (can be seen as infinite, i assume), compared to the active elemen=
t (gate of the FET). Perhaps there will also be a better coupling to qrm=
 sources? I also have to make some measurements. The antennas we use are=
 comparale i think. So we could share (all) share our experiences :-)
>     =20
>     A special question comes up when a optic fiber cable is used, since=
 in a coax application there remains a high C of the ground electrode, eve=
n when a symmetrical transformer is used (since the active element has jus=
t a few pF to the far field). That special question is: What will happen,=
 when the case/ground electrode becomes small against the active element=
 (e.g. circuit in SMD, small battery inside)?! Will there be a change in=
 the optimal C of the active element to the far field? I assume, then, one=
 has to define an optimal C ratio of both electrodes. Will it behave as a=
 short dipole? And what about a short vertical (30cm) active antenna that=
 is directly placed on the ground with a almost ideal conducting ground pl=
ane, e.g. aluminium foil (out of the household) in a radius of 1m (ignorin=
g the local qrm problem, so e.g. in your garden, apart from the city)?
>     =20
>     On my new qth i made first steps to receive LF with the active anten=
na mounted just 2m above ground but hung up on a wet tree. Results were vy=
 bad. I thought that SNR could be better when increasing the active elemen=
t since signals were weak (DCF39 at S7), but it wasn't. The optimal length=
 was still 30cm. That seems not only to be "sufficient" but rather optimal=
! So less and more is worse, unaffected by the hight above gnd?
>     =20
>     I think one has to imagine the E-Field lines that are going through=
 the ambience. The fieldstrength seems just to be very small in a lossy en=
vironment (on my hill, where no trees can be found, the antenna was also=
 2m up and DCF39 was S9+20). So hight above ground seems to essencial, eve=
n without local qrm. Each decrease of input signal can be compensated by=
 more gain but SNR decreases, of course.
>     =20
>     What are your ideas to these thoughts? What do you think will happen=
 if the ground-electrode-C becomes small against the C of the active eleme=
nt? What will be the optimum C for both? Will the electrodes have the same=
 "importance", like as a short dipole? Questions over Questions ;-)=20
>     =20
>     Recently i had the idea to test that with a variable antenna of a /p=
 UKW radio, perhaps two for each electrode. That will be interesting to pl=
ay with ;-)
>     =20
>     73!! Stefan/DK7FC
>=20
> ________________________________
>=20
>     Von: owner-rsgb_lf_group@blacksheep.org im Auftrag von Roelof Bakker
>     Gesendet: Sa 06.02.2010 13:53
>     An: rsgb_lf_group@blacksheep.org
>     Betreff: Re: LF: AW: Re: test signal wanted
>    =20
>    =20
>=20
>     Hello Stefan,
>    =20
>     Probably a bit late, bit I have been told that an active whip won't=
 work=20
>     well on a metalic mast.
>     I never tried it myself (still on the to do list) due to lack of a=
=20
>     suitable mast.
>    =20
>     73,
>     Roelof, pa0rdt
>    =20
>    =20
--=20
73 es gd dx de pat g4gvw
 qth nr felixstowe uk
(east coast, county of suffolk)