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 w9UAUgbd024468 for ; Tue, 30 Oct 2018 11:30:48 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gHRDx-0004lz-S1 for rs_out_1@blacksheep.org; Tue, 30 Oct 2018 10:26:13 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gHRDx-0004lq-0v for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 10:26:13 +0000 Received: from rgout0805.bt.lon5.cpcloud.co.uk ([65.20.0.152]) by relay1.thorcom.net with esmtp (Exim 4.91_59-0488984) (envelope-from ) id 1gHRDt-0002VL-IY for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 10:26:11 +0000 X-OWM-Source-IP: 86.158.119.119 (GB) X-OWM-Env-Sender: alan.melia@btinternet.com X-RazorGate-Vade-Classification: clean X-RazorGate-Vade-Verdict: clean 0 X-VadeSecure-score: verdict=clean score=0/300, class=clean X-SNCR-VADESECURE: CLEAN X-RazorGate-Vade-Verdict: clean 0 X-RazorGate-Vade-Classification: clean X-RazorGate-Vade: gggruggvucftvghtrhhoucdtuddrgedtkedriedtgdduhecutefuodetggdotefrodftvfcurfhrohhfihhlvgemuceutffkvffkuffjvffgnffgvefqofdpqfgfvfenuceurghilhhouhhtmecufedttdenucenucfjughrpefkhffvfhfuffggtgfrigfoqfesrgdtjeepuddtudenucfhrhhomhepfdetlhgrnhcuofgvlhhirgdfuceorghlrghnrdhmvghlihgrsegsthhinhhtvghrnhgvthdrtghomheqnecuffhomhgrihhnpehhrghmqdhrrgguihhoqdhophdrnhgvthenucfkphepkeeirdduheekrdduudelrdduudelnecurfgrrhgrmhephhgvlhhopehgnhgrthdpihhnvghtpeekiedrudehkedrudduledrudduledpmhgrihhlfhhrohhmpeeorghlrghnrdhmvghlihgrsegsthhinhhtvghrnhgvthdrtghomheqpdhrtghpthhtohepoehrshhgsggplhhfpghgrhhouhhpsegslhgrtghkshhhvggvphdrohhrgheqnecuvehluhhsthgvrhfuihiivgeptd Received: from gnat (86.158.119.119) by rgout08.bt.lon5.cpcloud.co.uk (9.0.019.26-1) (authenticated as alan.melia@btinternet.com) id 5BC47A8701374614 for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 10:26:09 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=btinternet.com; s=btcpcloud; t=1540895169; bh=y5tdycZzwIdqxlryd8K6MMk/wYjCSCMGLo1hKUr2z1E=; h=Message-ID:From:To:References:Subject:Date:MIME-Version:X-Mailer; b=kFOYXvsQOKSsK8CL/Q2Th7nBeuYsLWCMw6LZfBUqut8/v7PskOeryRdkjJQ8vJqdCAMmZGDN73/wUcWFrx0D1cWCaEPOTzM1SFkSUWgs4tIcYmlpMy+/mm+6wkwdVGzaQx9n0l6A7rfy8wapnkoyClTGIy74p5B3iK13oMPvL1k= Message-ID: <74FF0F2A528B4364ABFAB49EE24607B1@gnat> From: "Alan Melia" To: References: <166b64cbe61.marcocadeddu@tin.it> <6DB8451D7F3D3947A5918808A59621EA0867FDA1@servigilant.vigilant.local> <5BD5D50A.4060405@posteo.de> <6DB8451D7F3D3947A5918808A59621EA0868096B@servigilant.vigilant.local> <6DB8451D7F3D3947A5918808A59621EA08680E17@servigilant.vigilant.local> Date: Tue, 30 Oct 2018 10:26:06 -0000 MIME-Version: 1.0 X-Priority: 3 X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook Express 6.00.2900.5931 X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 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: 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. [...] 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 [65.20.0.152 listed in list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 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: b00ff688df97da26ae1d4b9e6e5f2479 Subject: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received) Content-Type: multipart/alternative; boundary="----=_NextPart_000_001B_01D4703A.F753B7E0" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: ** X-Spam-Status: No, hits=2.1 required=5.0 tests=FORGED_MUA_OUTLOOK,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 This is a multi-part message in MIME format. ------=_NextPart_000_001B_01D4703A.F753B7E0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable 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 -----=20 From: VIGILANT Luis Fern=E1ndez=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Tuesday, October 30, 2018 9:53 AM Subject: RE: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: = EA5DOM received) Hi Alan, LF =20 Thank you for your comments =20 Yes, the coil is at the antenna, at the end of the 30m coax line. = Attached is a sweep between 8 and 300Khz There is only one resonance at 137KHz as you can see =20 73 de Luis EA5DOM =20 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) =20 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 your VNA may have a wide band detector which would respond to = harmonic power?? I suppose a sweep at 270kHz would check this ? =20 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 think that rain water would be high resistance, and until it had = time to disolve 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! =20 =20 Alan G3NYK ----- Original Message -----=20 From: VIGILANT Luis Fern=E1ndez=20 To: rsgb_lf_group@blacksheep.org=20 Sent: Monday, October 29, 2018 5:34 PM Subject: RE: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 = Hz: EA5DOM received) =20 Hi Stefan, LF =20 > 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't check if = calibration is correct but better than nothing Yes, the output waveform from PA is a perfect sine in the scope =20 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. =20 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 =20 I'm not measuring the antenna at feed point but via 30m RG58 coax. = The analyzer is compensating for this cable anyway =20 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 =20 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't save the current measurements at 12V. But with 24V I got = 114Vrms over dummy load and the PA current was 16A@24V =20 73 de Luis EA5DOM =20 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) =20 Hi Luis, Am 27.10.2018 23:11, schrieb VIGILANT Luis Fern=E1ndez:=20 Hi All, LF=20 =20 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.=20 Other intringuin detail. When it is dry and impedance rises to = >100 Ohm the only way to hardly reach 1A RF=20 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.=20 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 =20 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 =20 Have not tried without LPF. The analyzer measurements are made = directly to antenna. But may be a good idea to make them with the LPF inserted and see what happens =20 73 de Luis EA5DOM =20 -------------------------------------------------------------------------= - De: owner-rsgb_lf_group@blacksheep.org = [owner-rsgb_lf_group@blacksheep.org] en nombre de marcocadeddu@tin.it = [marcocadeddu@tin.it] Enviado: s=E1bado, 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 and much similar to mine: roof based antennas with elevated ground = (in my case) 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 correctly, 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 =20 ----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, >=20 >> Impedance drops a lot after rain >=20 > 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. >=20 >=20 > 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. >=20 > Best 73, Markus >=20 > Von: VIGILANT Luis Fern=E1ndez >=20 > 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. ------=_NextPart_000_001B_01D4703A.F753B7E0 Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Ok Luis I remembered after I posted, = that I think=20 Andy's loading 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 = memory.
 
Alan
----- Original Message -----
From:=20 VIGILANT = Luis=20 Fern=E1ndez
Sent: Tuesday, October 30, 2018 = 9:53=20 AM
Subject: RE: Antenna resistance = (Re: LF:=20 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.=20 Attached is a sweep between 8 and 300Khz

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

 

73 de Luis

EA5DOM

 

De:=20 owner-rsgb_lf_group@bl= acksheep.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)

 

Luis=20 you mention measuring at the end of 30m of coax. Presumably the = loading coil=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 = reported=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 = sweep=20 at 270kHz would check this ?

 

My=20 measurements of antenna+loss resistance were made with the antenna = unloaded=20 (not tuned) The equivalenct should be a series resistance and=20 capacitance. Finbar EI0CF made many measurements on our = inductively top=20 loaded system. (see http://g3nyk.ham-rad= io-op.net/spiraltop.htm=20 ) We found that the resistance increased during rain but = recovered soon=20 after it ceased. I=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 = from=20 the soil the ground resistivity would be high. Of course it never = rained=20 when we wanted to test this but a gale destroyed the system.The spiral = top-load catches a lot of wind!   

 

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 = received)

 

Hi Stefan, LF

 

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

I have an old thermocouple Amp meter, 4A range. = Couldn=92t check if=20 calibration is correct but better than nothing

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

 

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

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

at the same point were SWR is = minimum.

 

Attached two charts corresponding 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 = day it=20 dropped to 32 Ohm

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

 

I=92m not measuring the antenna at feed point but via = 30m RG58=20 coax. The analyzer is compensating for this cable=20 anyway

 

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

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

 

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

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

Didn=92t save the current measurements at 12V. But with = 24V I got=20 114Vrms over dummy load and the PA current was = 16A@24V

 

73 de Luis

EA5DOM

 

De:=20 owner-rsgb_lf_group@bl= acksheep.org=20 [mailto:owner-rsgb_lf_g= roup@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 = received)

 

Hi Luis,

Am = 27.10.2018 23:11,=20 schrieb VIGILANT Luis Fern=E1ndez:

Hi=20 All, LF

 

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 = then 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 voltage at antenna feed. = Running=20 the antenna at the optimum resonance = makes

almost no RF current, even considering 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 = need a=20 transformer to transform it to 50 Ohm. Or your LPS is not working = properly.=20 What power output do you get when using a 50 Ohm dummy load? And = what=20 efficiency?

73, Stefan


 

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

https://www.dropbox.com/s/ejn5stuz7vban7u/Ropex%20Schematic.= JPG?dl=3D0

 

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

 

73 de=20 Luis

EA5DOM

 

De: = owner-rsgb_lf_group@blacksheep.org = [owner-rsgb_lf_group@blacksheep.org] en = nombre de=20 marcocadeddu@tin.it = [marcocadeddu@tin.it]
Enviado:=20 s=E1bado, 27 de octubre de 2018 18:12
Para: rsgb_lf_group@blacksheep.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 = location=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 = vertical=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 past 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
 

----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 = Autodecoder 137490=20 Hz: EA5DOM received)

Hi Luis, Markus, LF

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

My antenna resistance is very = high,=20 usually more than 100 ohms. I
think there may be a few reasons. = There=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 = minimize=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 = ground=20 are tied together.
I suppose this is because more noise is = radiated=20 from the TX
antenna, then picked up by the RX antenna which has = its own=20 small,
isolated ground.

Rain has no effect on the = antenna=20 resistance, but temperature does.
During summer there is little = change,=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 = continues 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
watt=20 using the measured resistance, antenna parameters and = current.
But does=20 this calculation include all the losses in trees? If I had
the = proper=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 = normally=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 = and 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
>=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
> water=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=E1ndez
>=20
> I'm struggling
> here with the antenna. Most of the = 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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