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The original message has been attached to this so you can view it (if it isn't spam) or label similar future email. If you have any questions, see the administrator of that system for details. Content preview: LF, I have experienced that any lossy elements around the antenna affect feedpoint resistance, and hence antenna current. [...] Content analysis details: (-0.5 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [220.209.183.60 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record -0.5 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: 3aadd9fea9ba15034c375823b9f54189 Subject: RE: LF: Re: Ant current Content-Type: multipart/alternative; boundary="----=_NextPart_000_00FD_01CF2002.1456CCD0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: * X-Spam-Status: No, hits=1.1 required=5.0 tests=FROM_ENDS_IN_NUMS,HTML_50_60, HTML_MESSAGE autolearn=no version=2.63 X-SA-Exim-Scanned: Yes Sender: owner-rsgb_lf_group@blacksheep.org Precedence: bulk Reply-To: rsgb_lf_group@blacksheep.org X-Listname: rsgb_lf_group X-SA-Exim-Rcpt-To: rs_out_1@blacksheep.org X-SA-Exim-Scanned: No; SAEximRunCond expanded to false This is a multipart message in MIME format. ------=_NextPart_000_00FD_01CF2002.1456CCD0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable LF, =20 I have experienced that any lossy elements around the antenna affect = feedpoint resistance,=20 and hence antenna current. With my antenna on the roof, the roofing material was lossy enough,=20 the antenna mounting "leg"s were lossy, the feeding wire (PVC) was lossy also,=20 and covering them with wire mesh, replacing PVC-wire to PE-wire, = etc.,etc,=20 reduced my feedpoint resistance, from about 60ohm to 30ohm, at 136kHz, when I was using a coil of 15ohm(136kHz) and ground resistance of 10ohm = (AF, measured). A few ohms was left as unsolved unknown loss. =20 I felt, ground is an imperfect conductor, is lossy, many surrounding materials are imperfect insulator, are lossy, (the roof, the house, trees, ....) unless they are chosen to be low loss. =20 Hideho YAMAMURA / JF1DMQ =20 =20 =20 From: owner-rsgb_lf_group@blacksheep.org = [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of hvanesce Sent: Sunday, February 02, 2014 9:07 AM To: rsgb_lf_group@blacksheep.org Subject: RE: LF: Re: Ant current =20 Markus, =20 Well said.=20 =20 73, Jim AA5BW =20 =20 From: owner-rsgb_lf_group@blacksheep.org = [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of Markus Vester Sent: Saturday, February 1, 2014 3:47 PM To: rsgb_lf_group@blacksheep.org Subject: Re: LF: Re: Ant current =20 The apparent contradiction (why is higher impedance better?) is easy to = understand if you look at surrounding trees as capacitively coupled = shunt resistors. The loss contribution At the antenna can be deduced by = transforming the series impedance=20 -j X + R into a parallel shunt cunductance, whose real part will be G =3D R / (R^2 + X^2) Obviously G disappears when R is infinite (tree is transparent) or zero = (tree is a metal pole), and reaches a broad maximum when R ~ X. =20 While the coupling capacitance X is determined by shape and size, the = resistance of the tree trunk and twigs varies with humidity and = temperature. During frost conditions, the sap is retracted and R becomes = much larger than X, thus G becomes very small. On the other hand, when = trees are wet, R is approaching X, and antenna losses G go up. For a = backyard amateur antenna, capacitive coupling to vegetation can easily = be the dominant loss mechanism, exceeding the series resistances of the = ground connection and the coil. =20 Another effect is that partial shunting of displacement currents to = ground reduces effective height - with a given input current less is = getting out to the far field. A few years ago, I found by measurements = that my antenna efficiency almost doubled in a cold winter night: The = loss resistance went down by 30%, and the effective hight grew by 20%, = so each effect was contributing roughly 1.5 dB. =20 =20 Best 73, Markus (DF6NM) =20 =20 =20 =20 ----- Original Message -----=20 From: phl@netikka.fi=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Saturday, February 01, 2014 9:40 PM Subject: Re: LF: Re: Ant current =20 Christian, LF "Ice is an insulator" If this is true it also means that all lossy trees in the surrounding =20 may have turned into nearly insulators. Unless there is ice or frost on my antenna and insulators I usually =20 have a lower Rtot (more antenna current) in the winter. This is in =20 line with your findings. It may well be lower environmental losses and =20 not the ground loss that are resonsible for this phenomenon here as my =20 antenna has lots of trees in the vincinity. BR Paul-Henrik, OH1LSQ Quoting Alan Melia : > Wet ground is lossy, ice is an insulator, antenna current is mainly =20 > determined by Rloss ?? If you measure the unloaded antenna with a =20 > bridge, you will measure values for C and Rtotal. Rtotal include =20 > Rrad and Rloss. Rrad is very smal for amateur size amtennas and =20 > doesnt change much. So the Ground loss must be reduced. > > Alan > G3NYK > ----- Original Message ----- From: "C. Groeger" > To: > Sent: Saturday, February 01, 2014 2:51 PM > Subject: LF: Ant current > > >> Hi all >> How can one explain that ant current rises when soil is frozen? >> >> Conductivity of water should be much higher than that of ice. >> >> So earth resistance would be higher and the current should drop =20 >> when soil is frozen... >> >> 73, df5qg >> >> >> Christian Groeger ------=_NextPart_000_00FD_01CF2002.1456CCD0 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

LF,

 

I have experienced that any = lossy elements around the antenna affect feedpoint resistance, =

and hence antenna = current.

With my antenna on the roof, the = roofing material was lossy enough,

the antenna mounting = "leg"s were lossy,

the feeding wire (PVC) was lossy = also,

and covering them with wire = mesh, replacing PVC-wire to PE-wire, etc.,etc,

reduced my feedpoint resistance, = from about 60ohm to 30ohm, at 136kHz,

when I was using a coil of = 15ohm(136kHz) and ground resistance of 10ohm (AF, = measured).

A few ohms was left as unsolved = unknown loss.

 

I felt,

ground is an imperfect = =C2=A0conductor, is lossy,

many surrounding materials are = imperfect insulator, are lossy,

(the roof, the house, trees, = ....)

unless they are chosen to be low = loss.

 

Hideho YAMAMURA / = JF1DMQ

 

 

 

From:= = owner-rsgb_lf_group@blacksheep.org = [mailto:owner-rsgb_lf_group@blacksheep.org] On Behalf Of = hvanesce
Sent: Sunday, February 02, 2014 9:07 = AM
To: rsgb_lf_group@blacksheep.org
Subject: RE: LF: = Re: Ant current

 

Markus,

 

Well said.

 

73,  Jim AA5BW

 

 

From:= owner-rsgb_lf_group@bl= acksheep.org [mailto:owner-rsgb_lf_g= roup@blacksheep.org] On Behalf Of Markus = Vester
Sent: Saturday, February 1, 2014 3:47 PM
To: = rsgb_lf_group@blacksheep.org=
Subject: Re: LF: Re: Ant = current

 

The apparent = contradiction (why is higher impedance better?) is easy to understand if = you look at surrounding trees as capacitively coupled shunt resistors. = The loss contribution At the antenna can be deduced by transforming = the series impedance

 -j X + = R

into a = parallel shunt cunductance, whose real part will be

 G =3D = R / (R^2 + X^2)

Obviously G = disappears when R is infinite (tree is transparent) or zero (tree is a = metal pole), and reaches a broad maximum when R ~ X.

 

While the = coupling capacitance X is determined by shape and size, the = resistance of the tree trunk and twigs varies with humidity = and temperature. During frost conditions, the sap is retracted and = R becomes much larger than X, thus G becomes very small. On = the other hand, when trees are wet, R is approaching X, and antenna = losses G go up. For a backyard amateur antenna, capacitive coupling = to vegetation can easily be the dominant loss mechanism, exceeding = the series resistances of the ground connection and the = coil.

 

Another = effect is that partial shunting of displacement currents to ground = reduces effective height - with a given input current less is getting = out to the far field. A few years ago, I found by measurements that = my antenna efficiency almost doubled in a cold winter night: = The loss resistance went down by 30%, and the effective hight grew by = 20%, so each effect was contributing roughly 1.5 = dB.   

 

Best = 73,

Markus = (DF6NM)

 

 

 

 

----- = Original Message -----

From:<= /b> phl@netikka.fi =

Sent:<= /b> Saturday, = February 01, 2014 9:40 PM

Subject: Re: LF: Re: = Ant current

 

Christian, = LF

"Ice is an insulator"

If this is true it also = means that all lossy trees in the surrounding 
may have turned = into nearly insulators.


Unless there is ice or frost on my = antenna and insulators I usually 
have a lower Rtot (more = antenna current) in the winter. This is in 
line with your = findings. It may well be lower environmental losses and 
not = the ground loss that are resonsible for this phenomenon here as my  =
antenna has lots of trees in the = vincinity.


BR

Paul-Henrik, = OH1LSQ



Quoting Alan Melia <alan.melia@btinternet.com&g= t;:

> Wet ground is lossy, ice is an insulator, antenna = current is mainly 
> determined by Rloss ?? If you measure = the unloaded  antenna with a 
> bridge, you will = measure values for C and Rtotal. Rtotal include 
> Rrad and = Rloss. Rrad is very smal for amateur size amtennas and 
> = doesnt change much. So the Ground loss must be reduced.
>
> = Alan
> G3NYK
> ----- Original Message ----- From: "C. = Groeger" <aot.aot@gmx.de>
> To: <rsgb_lf_group@blacksheep.org= >
> Sent: Saturday, February 01, 2014 2:51 PM
> = Subject: LF: Ant current
>
>
>> Hi all
>> = How can one explain that ant current rises when soil is = frozen?
>>
>> Conductivity of water should be much = higher than that of ice.
>>
>> So earth resistance = would be higher and the current should drop 
>> when soil = is frozen...
>>
>> 73, = df5qg
>>
>>
>> Christian = Groeger


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