Return-Path: Received: from post.thorcom.com (post.thorcom.com [195.171.43.25]) by klubnl.pl (8.14.4/8.14.4/Debian-8+deb8u2) with ESMTP id w9UAf2ak024533 for ; Tue, 30 Oct 2018 11:41:08 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gHRO0-0004ra-4H for rs_out_1@blacksheep.org; Tue, 30 Oct 2018 10:36:36 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gHRNv-0004rR-D6 for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 10:36:31 +0000 Received: from mail-ed1-x536.google.com ([2a00:1450:4864:20::536]) by relay1.thorcom.net with esmtps (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.91_59-0488984) (envelope-from ) id 1gHRNs-0002XO-Fb for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 10:36:30 +0000 Received: by mail-ed1-x536.google.com with SMTP id x2-v6so10009675eds.3 for ; Tue, 30 Oct 2018 03:36:28 -0700 (PDT) X-DKIM-Result: Domain=gmail.com Result=Good and Known Domain DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to; bh=Dq13OaYwcBEE5yuFlM8L0XkiRWrGoaE8qJhNnr/yfrY=; b=rQkm2Za5+oZFiLnDFhg8g/L7dmbCc3+5aL4qnx7gwnMObzIwPLqJuOZqJybuKatOWc iwWgr6LWzV7g3lZzQMlIfrXfnjcTWYCmyt8p7UChLJSxLq4Ahcc9cmF86nE2po2VRexh 60CEzCWZ5/5K96KU2wrqcHxqkrOxE5SCcJNf9aTOT0VZQn+WBxIMG0Bi+LC7c1J3X6Ft Xgqq/dfRLlS3ntrJ1xE6qi65uGOe3EAvd8ZVVhCA27c6c6iwTQ5P6mMLaK9cHVmDP2p+ 0GGHQoE6l+X08SJuUXRYx6vk7PrlV98GYgfee7oKJGjY79rBc0UQYRLhvm0O9jH4IOAh D/Gw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to; bh=Dq13OaYwcBEE5yuFlM8L0XkiRWrGoaE8qJhNnr/yfrY=; b=rYtLRnr+sG6FXJgF7XR3KK9XuGB3hXyLqOvLfmmet9NSGywYEWN4d6T8tM1LbDP+qT /Tn6c1AFr5bV5JMNo67gYO2LJVHcebRtStPEk9TYNddyUV6R6vecx3MK6Z1dwQWFW2ym OJ76NxrD5QBqM7vNK1o1ExK1Pjqn8AsnS0IR5jVk6gGx79pmDWrVLoZyAfESvuAu/quP JxM5/dGIR3m57uwOcqYd1qhLoUVzdTNe7jrk+cfTeq/5rpAAOBifSwGejCDd8tRc497f y3cfRnb4btvv1bZ74ujUX6DBWX3qb9wLPAdyTKWEAaNqSP0FMiVJfo6a1LeSLVjZIwwo p8EA== X-Gm-Message-State: AGRZ1gLfYhy0d4fpaivTnW+qvjMc7ggedL685rIQjx84sgm4OKU0EXUk e5TMAMp06gGjz+2pUmnmPO2Bv8+mmxuoSJ+4dFq97A== X-Google-Smtp-Source: AJdET5dAsu/EW628vV056eRSh75OplP/qp5uSZx8vj7jQ1xJeyQbv/FSyWqK+uWtgndcbei0Su8i/urYm/z4OUOf+Vo= X-Received: by 2002:a17:906:64cb:: with SMTP id p11-v6mr12729090ejn.181.1540895787105; Tue, 30 Oct 2018 03:36:27 -0700 (PDT) MIME-Version: 1.0 References: <166b64cbe61.marcocadeddu@tin.it> <6DB8451D7F3D3947A5918808A59621EA0867FDA1@servigilant.vigilant.local> <5BD5D50A.4060405@posteo.de> <6DB8451D7F3D3947A5918808A59621EA0868096B@servigilant.vigilant.local> <6DB8451D7F3D3947A5918808A59621EA08680E17@servigilant.vigilant.local> <74FF0F2A528B4364ABFAB49EE24607B1@gnat> In-Reply-To: <74FF0F2A528B4364ABFAB49EE24607B1@gnat> From: Andy Talbot Date: Tue, 30 Oct 2018 10:36:15 +0000 Message-ID: To: LineOne X-Spam-Score: 0.0 (/) X-Spam-Report: Spam detection software, running on the system "relay1.thorcom.net", has NOT identified this incoming email as spam. The original message has been attached to this so you can view it or label similar future email. If you have any questions, see @@CONTACT_ADDRESS@@ for details. Content preview: Nope, the loading coil was outside and fed with 15m or so of coax. The issue I found was that there were two tuning points that had a purely resistive value. But the two real values of R were very far apart; the wanted one (about 100 ohms at 137, equal to mostly ground losses) and another with very high R caused by an L match transformation. [...] Content analysis details: (0.0 points, 5.0 required) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [2a00:1450:4864:20:0:0:0:536 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (andy.g4jnt[at]gmail.com) 0.0 HTML_MESSAGE BODY: HTML included in message 0.0 T_KAM_HTML_FONT_INVALID BODY: Test for Invalidly Named or Formatted Colors in HTML 0.0 T_DKIM_INVALID DKIM-Signature header exists but is not valid X-Scan-Signature: 7b63be0e4943c57b7a0948cae0832a5f Subject: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received) Content-Type: multipart/alternative; boundary="00000000000006c25305796fc283" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.5 required=5.0 tests=HTML_40_50,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 --00000000000006c25305796fc283 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Nope, the loading coil was outside and fed with 15m or so of coax. The issue I found was that there were two tuning points that had a purely resistive value. But the two real values of R were very far apart; the wanted one (about 100 ohms at 137, equal to mostly ground losses) and another with very high R caused by an L match transformation. It comes about like this. Start with the loading coil correctly tuned to give the 100R AT IT'S BASE. Add a tiny bit more L, then apply the shunt c of the short feeder. We now have a series L shunt C network and if the bit of extra L is the correct value it will transform to a higher value of R I found it, by testing with a small auxiliary coil indoors but that coil wasn't teh reason Andy www.g4jnt.com On Tue, 30 Oct 2018 at 10:29, Alan Melia wrote: > Ok Luis I remembered after I posted, that I think Andy's loading coil was > indoors fed by short coax run to the wire. So the capacitance of the coax > was across the link, or tapped section. Pure water is an odd substance it > was a very high dielectric constant .....around 80 from memory. > > Alan > > ----- Original Message ----- > *From:* VIGILANT Luis Fern=C3=A1ndez > *To:* rsgb_lf_group@blacksheep.org > *Sent:* Tuesday, October 30, 2018 9:53 AM > *Subject:* RE: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: > EA5DOM received) > > Hi Alan, LF > > > > Thank you for your comments > > > > Yes, the coil is at the antenna, at the end of the 30m coax line. Attache= d > is a sweep between 8 and 300Khz > > There is only one resonance at 137KHz as you can see > > > > 73 de Luis > > EA5DOM > > > > *De:* owner-rsgb_lf_group@blacksheep.org [mailto: > owner-rsgb_lf_group@blacksheep.org] *En nombre de *Alan Melia > *Enviado el:* lunes, 29 de octubre de 2018 20:15 > *Para:* rsgb_lf_group@blacksheep.org > *Asunto:* Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: > EA5DOM received) > > > > Luis you mention measuring at the end of 30m of coax. Presumably the > loading coil is at the antenna?? In which case you need to check that you > have not parasitic resonances at harmonics of the drive frequency. Andy > G4JNT reported some problems with that kind of set-up but shorter length = of > coax. Maybe you do have the coax matched?? I am not sure but I suspect yo= ur > VNA may have a wide band detector which would respond to harmonic power??= I > suppose a sweep at 270kHz would check this ? > > > > My measurements of antenna+loss resistance were made with the antenna > unloaded (not tuned) The equivalenct should be a series resistance and > capacitance. Finbar EI0CF made many measurements on our inductively top > loaded system. (see http://g3nyk.ham-radio-op.net/spiraltop.htm ) We > found that the resistance increased during rain but recovered soon after = it > ceased. I was never able to determine what the cause was. It was unlikely > to be increased insulator loss at the low bridge drive levels. I did thin= k > that rain water would be high resistance, and until it had time to disolv= e > salts from the soil the ground resistivity would be high. Of course it > never rained when we wanted to test this but a gale destroyed the > system.The spiral top-load catches a lot of wind! > > > > Alan > > G3NYK > > ----- Original Message ----- > > *From:* VIGILANT Luis Fern=C3=A1ndez > > *To:* rsgb_lf_group@blacksheep.org > > *Sent:* Monday, October 29, 2018 5:34 PM > > *Subject:* RE: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: > EA5DOM received) > > > > Hi Stefan, LF > > > > > How do you measure the antena current? Are you sure the waveform still > looks like a sine? > > I have an old thermocouple Amp meter, 4A range. Couldn=E2=80=99t check if > calibration is correct but better than nothing > > Yes, the output waveform from PA is a perfect sine in the scope > > > > Hm, are you sure your antenna has 50 Ohm when it is resonated? > > With the analyzer I can measure many parameters. Module of impedance and > also ancge of impedance, which cross zero > > at the same point were SWR is minimum. > > > > Attached two charts corresponding to measures made on Saturday and Sunday= . > You can see that antenna is resonating at about 138.500 > > and the cursors are at 137.511 and 138.078. In october 28th the impedance > is about 100 Ohm at resonance and next day it dropped to 32 Ohm > > We had some rain during weekend that caused this change in the impedance > > > > I=E2=80=99m not measuring the antenna at feed point but via 30m RG58 coax= . The > analyzer is compensating for this cable anyway > > > > Otherwise you may need a transformer to transform it to 50 Ohm. Or your > LPS is not working properly > > Tried a short transmission without LPF. Same results. No difference > > > > What power output do you get when using a 50 Ohm dummy load? And what > efficiency? > > Last time I checked this I was measuring 72Vrms over 50 Ohm dummy load, > about 100W > > Didn=E2=80=99t save the current measurements at 12V. But with 24V I got 1= 14Vrms > over dummy load and the PA current was 16A@24V > > > > 73 de Luis > > EA5DOM > > > > *De:* owner-rsgb_lf_group@blacksheep.org [ > mailto:owner-rsgb_lf_group@blacksheep.org > ] *En nombre de *DK7FC > *Enviado el:* domingo, 28 de octubre de 2018 16:26 > *Para:* rsgb_lf_group@blacksheep.org > *Asunto:* Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: > EA5DOM received) > > > > Hi Luis, > > Am 27.10.2018 23:11, schrieb VIGILANT Luis Fern=C3=A1ndez: > > Hi All, LF > > > > Interesting topic. Also happens in MF but in LF it gets more critical. > Must be a nightmare at VLF :( > > > Here it is more critcal on MF than on LF. At VLF it is quite uncritical > because the coil's resistance is a major part of the overall losses. > > Other intringuin detail. When it is dry and impedance rises to >100 Ohm > the only way to hardly reach 1A RF > > is to detune the antenna. I have to set the resonant peak at 138Khz and > then at 137,5 get even higher impedance > > and high SWR, but the antenna current rises and so the radiated signal. > > How do you measure the antena current? Are you sure the waveform still > looks like a sine? > > All this at the cost of more amps > > consumed by the PA and higer voltage at antenna feed. Running the antenna > at the optimum resonance makes > > almost no RF current, even considering that this is the minimum impedance > point. > > Hm, are you sure your antenna has 50 Ohm when it is resonated? Otherwise > you may need a transformer to transform it to 50 Ohm. Or your LPS is not > working properly. What power output do you get when using a 50 Ohm dummy > load? And what efficiency? > > 73, Stefan > > > > > About the LPF, this is really the only part of the Ropex PA still in use. > This is a link to the schematic with the LPF > > https://www.dropbox.com/s/ejn5stuz7vban7u/Ropex%20Schematic.JPG?dl=3D0 > > > > Have not tried without LPF. The analyzer measurements are made directly t= o > antenna. But may be a good idea to > > make them with the LPF inserted and see what happens > > > > 73 de Luis > > EA5DOM > > > ------------------------------ > > *De:* owner-rsgb_lf_group@blacksheep.org [ > owner-rsgb_lf_group@blacksheep.org] en nombre de marcocadeddu@tin.it [ > marcocadeddu@tin.it] > *Enviado:* s=C3=A1bado, 27 de octubre de 2018 18:12 > *Para:* rsgb_lf_group@blacksheep.org > *Asunto:* R: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: > EA5DOM received) > > Hi Paul, Luis, Markus, LF > > let me join the topic ;-) > the antenna location of Luis is something else of your Markus and Paul an= d > much similar to mine: roof based antennas with elevated ground (in my cas= e) > and vertical ground (the water pipe) for Luis. > Anyway also in my case the serie resistance of my antenna increases with > rain (almost doubles). > But.. Luis, probably assumes the lower impedance basing on the higher > current. > Luis, what kind of LPF have you adopted? > Now I have a T filter with no shunting cap at the input and impedance > increases with rain both with and without LPF, but if I remember correctl= y, > when in the past I had an PI LPF with shunting input and output caps the > impedance in my shack was transformed from the transmission line and LPF > giving lower impedance by rain. > > Could be an explication? > > By the way, just for fate it's raining also here and I made some > measurement when dry again will repeat ;-) > > Have a funny weekend LF > > Marco IK1HSS > > > ----Messaggio originale---- > Da: paul@n1bug.com > Data: 27-ott-2018 12.34 > A: > Ogg: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM > received) > > Hi Luis, Markus, LF > > This is a very interesting topic for me too. > > My antenna resistance is very high, usually more than 100 ohms. I > think there may be a few reasons. There are trees near the antenna > which I presume to be lossy. My antenna ground system is not tied > into the house ground, in order to minimize 120 Hz sidebands on my > transmitted signal. When I tie the grounds together the level of > these sidebands increases almost 20 dB. Also my RX antenna is more > noisy when the TX antenna ground and house ground are tied together. > I suppose this is because more noise is radiated from the TX > antenna, then picked up by the RX antenna which has its own small, > isolated ground. > > Rain has no effect on the antenna resistance, but temperature does. > During summer there is little change, just minor variations. But as > the temperature drops and begins to approach freezing, resistance > begins to get lower. There is a big drop right around freezing or > few degrees below, but resistance continues to drop with even lower > temperatures, reaching minimum on the coldest winter nights. Last > winter I saw it reach 40 ohms a few times. :) > > I am no expert but I guess the trees are partly responsible for the > high resistance and the drop with freezing temperature? > > Anyway I can run enough power to reach calculated 1W EIRP and it's > enough to be heard across that little pond. :) > > But here is a related question: I have calculated my EIRP to be one > watt using the measured resistance, antenna parameters and current. > But does this calculation include all the losses in trees? If I had > the proper equipment to make field strength measurements at a > distance, would I find that my EIRP is less than one watt due to the > tree losses? > > 73, > Paul N1BUG > > > > On 10/27/18 5:45 AM, Markus Vester wrote: > > Hi Luis, > > > >> Impedance drops a lot after rain > > > > This seems unusual. I have exactly the opposite effect here: > > Series resistance at 137 kHz is normally around 20 ohms > > (including 5 ohms for the coil). When it rains it get worse up to > > about 40 ohms, whereas best times are cold and dry winter days > > with ~15 ohms when the trees are solidly frozen. So I presume > > that the major contribution to my resistance are > > capacitively-coupled losses in vegetation and other nearfield > > environment. The ground connection itself (the "house earth" > > which is connected to electric grid PE, and also pipe systems for > > water supply and distict heating) seems to have a low resistance. > > > > > > My only explanation for lower wet resistance would be if one were > > using a separate radial system in the garden, whose connection to > > ground might be better when the lawn is soaked. But I don't think > > this applies to your setup at all. > > > > Best 73, Markus > > > > Von: VIGILANT Luis Fern=C3=A1ndez > > > > I'm struggling > > here with the antenna. Most of the time impedance rises and I > > hardly run 1A RF current > > > > Rainy weekend here. > > Impedance drops a lot after rain. Let's see how much current can > > drainLast time I could see almost 4A RF. > > --00000000000006c25305796fc283 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Nope, the loading coil was=C2=A0 outside and fed= with 15m or so of coax.=C2=A0 =C2=A0The issue I found was that there were = two tuning points that had a purely resistive value.=C2=A0 But the two real= values of R were very far apart; the wanted one (about 100 ohms at 137, eq= ual to mostly ground losses) and another with very high R caused by an L ma= tch transformation.

It comes about like = this.=C2=A0 Start with the loading coil correctly tuned to give the 100R AT= IT'S BASE.=C2=A0 Add a tiny bit more L, then apply the shunt c of the = short feeder.=C2=A0 We now have a series L shunt C network and if the bit o= f extra L is the correct value it will transform to a higher value of R

I found it, by testing with a small auxilia= ry coil indoors but that coil wasn't teh reason


<= div dir=3D"ltr">


On Tue, 30 Oct 2018 at 10:29, Alan Melia <alan.melia@btinternet.com> = wrote:
Ok Luis I remembered after I posted, t= hat I think=20 Andy's=C2=A0loading coil was indoors fed by short coax run to the wire.= So the=20 capacitance of the coax was across the link, or tapped section. Pure water = is an=20 odd substance it was a very high dielectric constant .....around 80 from=20 memory.
=C2=A0
Alan
----- Original Message -----
Sent: Tuesday, October 30, 2018 9:5= 3=20 AM
Subject: RE: Antenna resistance (Re= : LF:=20 EbNaut Autodecoder 137490 Hz: EA5DOM received)

Hi Alan, LF

=C2=A0

Thank you for your comme= nts

=C2=A0

Yes, the coil is at the = antenna, at the end of the 30m coax line.=20 Attached is a sweep between 8 and 300Khz

There is only one resona= nce at 137KHz as you can=20 see

=C2=A0

73 de Luis=

EA5DOM

=C2=A0

De:=20 o= wner-rsgb_lf_group@blacksheep.org=20 [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de Alan=20 Melia
Enviado el: lunes, 29 de octubre de 2018 20:15
Para= :=20 rsgb_lf= _group@blacksheep.org
Asunto: Re: Antenna resistance (Re: LF:= =20 EbNaut Autodecoder 137490 Hz: EA5DOM=20 received)

=C2=A0

Luis=20 you mention measuring at the end of 30m of coax. Presumably the loading c= oil=20 is at the antenna?? In which case you need to check that you have not=20 parasitic resonances at harmonics of the drive frequency. Andy G4JNT repo= rted=20 some problems with that kind of set-up but shorter length of coax. Maybe = you=20 do have the coax matched?? I am not sure but I suspect your VNA may have = a=20 wide band detector which would respond to harmonic power?? I suppose a sw= eep=20 at 270kHz would check this ?

=C2=A0<= /u>

My=20 measurements of antenna+loss resistance were made with the antenna unload= ed=20 (not tuned) The equivalenct should be a series resistance and=20 capacitance.=C2=A0Finbar EI0CF made many measurements on our inductively = top=20 loaded system. (see http://g3nyk.ham-radio-op.net/spiraltop.htm=20 )=C2=A0We found that the resistance increased during rain but recovered s= oon=20 after it ceased.=C2=A0I=20 was never able to determine what the cause was. It was unlikely to be=20 increased insulator loss at the low bridge drive levels. I did think that= rain=20 water would be high resistance, and until it had time to disolve salts fr= om=20 the soil=C2=A0the ground resistivity would be high. Of course it never ra= ined=20 when we wanted to test this but a gale destroyed the system.The spiral=20 top-load catches a lot of wind!=C2=A0=C2=A0=C2=A0

=C2=A0<= /u>

Alan

G3NYK

-----=20 Original Message -----

Sent:=20 Monday, October 29, 2018 5:34 PM

Subject:= =20 RE: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM=20 received)

=C2=A0

Hi Stefan, LF

=C2=A0

> How do you measure the antena=20 current? Are you sure the waveform still looks like a sine?

I have an old thermoco= uple Amp meter, 4A range. Couldn=E2=80=99t check if=20 calibration is correct but better than nothing

Yes, the output wavefo= rm from PA is a perfect sine in the=20 scope

=C2=A0

Hm, are you sure your anten= na has 50 Ohm=20 when it is resonated?

With the analyzer I ca= n measure many parameters. Module of=20 impedance and also ancge of impedance, which cross=20 zero

at the same point were= SWR is minimum.

=C2=A0

Attached two charts co= rresponding to measures made on Saturday=20 and Sunday. You can see that antenna is resonating at about=20 138.500

and the cursors are at= 137.511 and 138.078. In october=20 28th the impedance is about 100 Ohm at resonance and next da= y it=20 dropped to 32 Ohm

We had some rain durin= g weekend that caused this change in the=20 impedance

=C2=A0

I=E2=80=99m not measur= ing the antenna at feed point but via 30m RG58=20 coax. The analyzer is compensating for this cable=20 anyway

=C2=A0

Otherwise you may need a tr= ansformer to=20 transform it to 50 Ohm. Or your LPS is not working properly

Tried a short transmis= sion without LPF. Same results. No=20 difference

=C2=A0

What power output do you ge= t when using=20 a 50 Ohm dummy load? And what efficiency?

Last time I checked th= is I was measuring 72Vrms over 50 Ohm dummy=20 load, about 100W

Didn=E2=80=99t save th= e current measurements at 12V. But with 24V I got=20 114Vrms over dummy load and the PA current was 16A@24V

=C2=A0

73 de Luis

EA5DOM

=C2=A0

De:=20 owner-rsgb_lf_group@blacksheep.org=20 [mailto:owner-rsgb_lf_group@blacksheep.org]=20 En nombre de DK7FC
Enviado el: domingo, 28 de octubre = de=20 2018 16:26
Para: rsgb_lf_group@blacksheep.org
Asunto:=20 Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM=20 received)

=C2=A0

Hi Luis,

Am 27.10.20= 18 23:11,=20 schrieb VIGILANT Luis Fern=C3=A1ndez:

Hi=20 All, LF

=C2=A0

Interesting topic. Also happens in = MF but in LF it gets more=20 critical. Must be a nightmare at VLF=20 :(


Here it=20 is more critcal on MF than on LF. At VLF it is quite uncritical because= the=20 coil's resistance is a major part of the overall losses.=20

Other=20 intringuin detail. When it is dry and impedance rises to >100 Ohm = the=20 only way to hardly reach 1A RF

is to=20 detune the antenna. I have to set the resonant peak at 138Khz and the= n at=20 137,5 get even higher impedance

and=20 high SWR, but the antenna current rises and so the radiated=20 signal.

How do you=20 measure the antena current? Are you sure the waveform still looks like = a=20 sine?

All=20 this at the cost of more amps

consumed by the PA and higer voltag= e at antenna feed. Running=20 the antenna at the optimum resonance makes

almost no RF current, even consider= ing that this is the minimum=20 impedance point.

Hm, are you=20 sure your antenna has 50 Ohm when it is resonated? Otherwise you may ne= ed a=20 transformer to transform it to 50 Ohm. Or your LPS is not working prope= rly.=20 What power output do you get when using a 50 Ohm dummy load? And what= =20 efficiency?

73, Stefan


=C2=A0

About=20 the LPF, this is really the only part of the Ropex PA still in use. T= his=20 is a link to the schematic with the LPF

=C2=A0

Have=20 not tried without LPF. The analyzer measurements are made directly to= =20 antenna. But may be a good idea to

make=20 them with the LPF inserted and see what=20 happens

=C2=A0

73 de=20 Luis

EA5DOM

=C2=A0

De: = owner-r= sgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] en nombre de=20 marcocade= ddu@tin.it [marcocadeddu@tin.it]
Enviado:=20 s=C3=A1bado, 27 de octubre de 2018 18:12
Para: rsgb_lf_group@blac= ksheep.org
Asunto:=20 R: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM= =20 received)

Hi Paul,=20 Luis, Markus, LF

let me join the topic ;-)
the antenna loca= tion=20 of Luis is something else of your Markus and Paul and much similar to= =20 mine: roof based antennas with elevated ground (in my case) and verti= cal=20 ground (the water pipe) for Luis.
Anyway also in my case the serie= =20 resistance of my antenna increases with rain (almost doubles).
But= ..=20 Luis, probably assumes the lower impedance basing on the higher=20 current.
Luis, what kind of LPF have you adopted?
Now I have a = T=20 filter with no shunting cap at the input and impedance increases with= rain=20 both with and without LPF, but if I remember correctly, when in the p= ast I=20 had an PI LPF with shunting input and output caps the impedance in my= =20 shack was transformed from the transmission line and LPF giving lower= =20 impedance by rain.

Could be an explication?

By the way,= just=20 for fate it's raining also here and I made some measurement when = dry again=20 will repeat ;-)

Have a funny weekend LF

Marco=20 IK1HSS
=C2=A0

----Messaggio originale----
Da: paul@= n1bug.com
Data: 27-ott-2018=20 12.34
A: <rsgb_lf_group@blacksheep.org>
Ogg: Antenna resistance (Re: LF: EbNaut A= utodecoder 137490=20 Hz: EA5DOM received)

Hi Luis, Markus, LF

This is a very= =20 interesting topic for me too.

My antenna resistance is very hi= gh,=20 usually more than 100 ohms. I
think there may be a few reasons. Th= ere=20 are trees near the antenna
which I presume to be lossy. My antenna= =20 ground system is not tied
into the house ground, in order to minim= ize=20 120 Hz sidebands on my
transmitted signal. When I tie the grounds= =20 together the level of
these sidebands increases almost 20 dB. Also= my=20 RX antenna is more
noisy when the TX antenna ground and house grou= nd=20 are tied together.
I suppose this is because more noise is radiate= d=20 from the TX
antenna, then picked up by the RX antenna which has it= s own=20 small,
isolated ground.

Rain has no effect on the antenna= =20 resistance, but temperature does.
During summer there is little ch= ange,=20 just minor variations. But as
the temperature drops and begins to= =20 approach freezing, resistance
begins to get lower. There is a big = drop=20 right around freezing or
few degrees below, but resistance continu= es to=20 drop with even lower
temperatures, reaching minimum on the coldest= =20 winter nights. Last
winter I saw it reach 40 ohms a few times.=20 :)

I am no expert but I guess the trees are partly responsible= for=20 the
high resistance and the drop with freezing=20 temperature?

Anyway I can run enough power to reach calculated= 1W=20 EIRP and it's
enough to be heard across that little pond. :)
But=20 here is a related question: I have calculated my EIRP to be one
wa= tt=20 using the measured resistance, antenna parameters and current.
But= does=20 this calculation include all the losses in trees? If I had
the pro= per=20 equipment to make field strength measurements at a
distance, would= I=20 find that my EIRP is less than one watt due to the
tree=20 losses?

73,
Paul N1BUG



On 10/27/18 5:45 AM,= =20 Markus Vester wrote:
> Hi Luis,
>
>> Impedance = drops=20 a lot after rain
>
> This seems unusual. I have exactly = the=20 opposite effect here:
> Series resistance at 137 kHz is normall= y=20 around 20 ohms
> (including 5 ohms for the coil). When it rains= it=20 get worse up to
> about 40 ohms, whereas best times are cold an= d dry=20 winter days
> with ~15 ohms when the trees are solidly frozen. = So I=20 presume
> that the major contribution to my resistance are
&= gt;=20 capacitively-coupled losses in vegetation and other nearfield
>= =20 environment. The ground connection itself (the "house earth"= ;
> which=20 is connected to electric grid PE, and also pipe systems for
> w= ater=20 supply and distict heating) seems to have a low resistance.
>= =20
>
> My only explanation for lower wet resistance would = be if=20 one were
> using a separate radial system in the garden, whose= =20 connection to
> ground might be better when the lawn is soaked.= But=20 I don't think
> this applies to your setup at all.
> =
>=20 Best 73, Markus
>
> Von: VIGILANT Luis Fern=C3=A1ndez>=20
> I'm struggling
> here with the antenna. Most of th= e time=20 impedance rises and I
> hardly run 1A RF current
>
>= ;=20 Rainy weekend here.
> Impedance drops a lot after rain. Let'= ;s see=20 how much current can
> drainLast time I could see almost 4A=20 RF.

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