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 w9UCXIRx025060 for ; Tue, 30 Oct 2018 13:33:26 +0100 Received: from majordom by post.thorcom.com with local (Exim 4.14) id 1gHT83-0005C3-FU for rs_out_1@blacksheep.org; Tue, 30 Oct 2018 12:28:15 +0000 Received: from [195.171.43.32] (helo=relay1.thorcom.net) by post.thorcom.com with esmtp (Exim 4.14) id 1gHT82-0005Bu-8p for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 12:28:14 +0000 Received: from smtp2web.tin.it ([212.216.176.236]) by relay1.thorcom.net with esmtp (Exim 4.91_59-0488984) (envelope-from ) id 1gHT80-0002nC-1S for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 12:28:13 +0000 Received: from feu13 (10.192.64.23) by smtp2web.tin.it (8.6.060.43) id 5B27C17303C32E24 for rsgb_lf_group@blacksheep.org; Tue, 30 Oct 2018 13:28:09 +0100 Received: from (93.146.209.118) by webmailtin.pc.tim.it; Tue, 30 Oct 2018 13:28:09 +0100 Message-ID: <166c4f20d8f.marcocadeddu@tin.it> Date: Tue, 30 Oct 2018 13:28:09 +0100 (CET) From: "marcocadeddu@tin.it" To: Mime-Version: 1.0 X-Originating-IP: 93.146.209.118:51200 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: Hi Luis, LF fine also from my side I'm planning a long funny weekend between repairs, adjustment and something new ;-) Just a further question: you wrote that your analyzer gives a lot of possible outputs.. and I'm a bit confused for the display SWR (what iis it? :-D ) and module of impedance. Could you display the same datas as a Smith chart? in this way you could see both resistive and reactive parts of the complex impedance changing with frequency which is helpful to understand what is going on. Pictures you shared show SWR vs frequency and |Z| vs. frequency but shows the R±jX form only on one frequency Marco, IK1HSS [...] 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 [212.216.176.236 listed in list.dnswl.org] -0.0 RCVD_IN_MSPIKE_H3 RBL: Good reputation (+3) [212.216.176.236 listed in wl.mailspike.net] -0.0 T_RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -0.0 SPF_PASS SPF: sender matches SPF record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (marcocadeddu[at]tin.it) 0.0 HTML_MESSAGE BODY: HTML included in message -0.0 RCVD_IN_MSPIKE_WL Mailspike good senders X-Scan-Signature: 7d2d9c344468c8a37a1113fa142438b6 Subject: R: RE: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM received) Content-Type: multipart/alternative; boundary="----=_Part_16618_31685788.1540902489514" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.8 required=5.0 tests=HTML_30_40,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 ------=_Part_16618_31685788.1540902489514 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi Luis, LF fine also from my side I'm planning a long funny weekend between repairs, a= djustment and something new ;-) Just a further question: you wrote that your analyzer gives a lot of possib= le outputs.. and I'm a bit confused for the display SWR (what iis it? :-D )= and module of impedance. Could you display the same datas as a Smith chart= ? in this way you could see both resistive and reactive parts of the comple= x impedance changing with frequency which is helpful to understand what is = going on. Pictures you shared show SWR vs frequency and |Z| vs. frequency b= ut shows the R=C2=B1jX form only on one frequency Marco, IK1HSS ----Messaggio originale---- Da: luis@vigilant.es Data: 30-ott-2018 12.23 A: "rsgb_lf_group@blacksheep.org" Ogg: RE: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5D= OM received) v\:* {behavior:url(#default#VML);} o\:* {behavior:url(#default#VML);} w\:* {behavior:url(#default#VML);} .shape {behavior:url(#default#VML);} --> Hi Marco, LF =20 The pipe runs inside the building in a narrow space. You are right, it is p= reserved from rain and there should be no effect at all It has been working nice in MF so far, and also first tests in LF were very= succesful. Last year I could even make a QRSS QSO with 9A3KB using the Ropex PA with minor modifications =20 Many variables here. I will rechek connection to the top section of the pip= e, which may be failing. And then dropping the wire parallel to the pipe if possible. We have a long weekend ahead which can be= ideal for this activities =E2=80=A6. at limit ;-) =20 >> My new 2nd DC receiver for MF is in service since a full day so for some= time I'll listen to MF wspr, see you later on LF =20 More rain here today and antenna wires are down. But sourprisingly I could = not get RF current yesterday even with low impedance Time to recheck PA with dummy load. May be I have a failure there too L =20 Oscar, LU1DOW had a fantastic night yesterday in MF. Spots from the States = and again LA2XPA May be he can try to send an EbNaut message and check if we can finally rec= eive him in central and south EU =20 73 de Luis EA5DOM =20 De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blackshe= ep.org] En nombre de marcocadeddu@tin.it Enviado el: lunes, 29 de octubre de 2018 17:52 Para: rsgb_lf_group@blacksheep.org Asunto: R: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA= 5DOM received) =20 Hi Luis, while I wish to thank Jay for the nice papers about ERP evaluation, whish t= o ask you a bit more info concerning the change of impedance. I understand that is not easy to access all "common parts" which often beca= me "everybody away from it!" I guess it should be feasible to drop a thin, = light wire from the top of the building till ground level for a short time = a take some measure to compare with your actual ground. In this way you should be able to understand if your water pipe is similar = or not to the wire (I'm speaking just to measure with a VNA or your analyze= r not to transmit high power which could be an hazard for people touching t= he momentary dropped wire). It is nice to read that you have seen the pipe junction bypassed from a str= ip: pipes have usually flanges to joint the sections ore threated ends, in = both cases the use of seals can interrupt the ground continuity: by the way= I suppose that for possible estinguish use, in the reservoir there is sweet water (maybe not drinkable but not se= a water!) and therefore the electrical continuity is granted from the steel= of the pipe and the ground strips not from water! water with low content o= f salts is almost an insulator rather than a conductor! If you have access to the pipe, you could drop the wire there and measure t= he dc resistance of the pipe against your wire, in the mean time I suggest = to check all those stripes even if I cannot understand why a bad contact on= one of the stripe could be rain sensitive... but I guess it is worth to do ;-) My new 2nd DC receiver for MF is in service since a full day so for some ti= me I'll listen to MF wspr, see you later on LF Marco, IK1HSS=20 ----Messaggio originale---- Da: luis@vigilant.es Data: 28-ott-2018 14.15 A: "rsgb_lf_group@blacksheep.org" Ogg: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM r= eceived) Hi Markus, LF =20 The pipe contains presurized water for the fire extinguish system. Is a "we= t colum" system. Pipe segments are connected with big brass links. Should be a good enought current conduc= tor. Down in the basement it connects with a pressure pump and a water reservoir tank, linked to the wat= er grid system =20 Will have to check the ground connections of all this stuff when possible. = Not easy But after all, we are all doing all this "not easy" things because it is no= t easy to work low bands, right? ;-) =20 Tested mains ground connection too and it helps a lot, but still depends on= rain. Access to the ground line at the lifts engines room on top building is complicated too, as I have no acc= ess there because of a AMHPS=20 (Anti Mad Ham Protection System) hi, hi =20 Installing my own ground line may be an option, but using light cable. As I= can only support the 80m cable at the top end, so weight must be low. Finally may be the best way to go =20 73 de Luis EA5DOM =20 De: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] en = nombre de Markus Vester [markusvester@aol.com] Enviado: domingo, 28 de octubre de 2018 0:21 Para: rsgb_lf_group@blacksheep.org Asunto: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DO= M received) > Something gets wet in the basement and the pipe gets a better connection = to ground, or at least to the water grid pipes, which finally run undergrou= nd Ah that must be the reason! That drain pipe is obviously not continuous met= al but inrterropted by some insulating joints or plastic sections, which ar= e more or less bypassed by a water film or flow when it rains. Could you try to use another ground connection which is continuous all the = way down? E.g. external lightning protection conductors, or even the protec= tive earth in your appartment? Best 73, Markus -----Urspr=C3=BCngliche Mitteilung----- Von: VIGILANT Luis Fern=C3=A1ndez An: rsgb_lf_group@blacksheep.org Verschickt: Sa, 27. Okt 2018 23:17 Betreff: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5D= OM received) Hi All, LF =20 Interesting topic. Also happens in MF but in LF it gets more critical. Must= be a nightmare at VLF :( =20 As Marco explained, our setup is not the usual at ground level in a propert= y plot. And in my case ther ground is 80m away down from the feed point, coil and capacitive topload. =20 Measured with the antenna analyzer I can see a drop in the impedance module= when all gets wet by rain It is not only an increase of RF current. Today I measured resistance from = the ground side of the feed point trought the pipe to building basement and then returning via the water grid= connecting the other side of the multimeter to a water pipe in my house: =20 4 Ohm measured early morning when it started with soft rain. At noon we had= stronger rain and in the afternoon I measured again. It dropped to 2 Ohm. Big difference. Something gets wet i= n the basement and the pipe gets a better connection to ground, or at least to the water grid pipes, which f= inally run underground =20 The top of the antenna is dismantled during storms, so can't measure impeda= nce with the analyzer right now but bet it is now well under 30 Ohm and would drain a few amps =20 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 the= n at 137,5 get even higher impedance and high SWR, but the antenna current rises and so the radiated signal. All= this at the cost of more amps consumed by the PA and higer voltage at antenna feed. Running the antenna a= t the optimum resonance makes almost no RF current, even considering that this is the minimum impedance p= oint.=20 =20 About the LPF, this is really the only part of the Ropex PA still in use. T= his 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=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 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 ra= in (almost doubles). But.. Luis, probably assumes the lower impedance basing on the higher curre= nt. Luis, what kind of LPF have you adopted? Now I have a T filter with no shunting cap at the input and impedance incre= ases 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 impeda= nce 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 measuremen= t 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 recei= ved) 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=C3=A1ndez >=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. =20 ------=_Part_16618_31685788.1540902489514 Content-Type: text/html;charset="UTF-8" Content-Transfer-Encoding: quoted-printable
Hi Luis, LF

fine also from my side I'm planni= ng a long funny weekend between repairs, adjustment and something new ;-)

Just a further question: you wrote that your analyz= er gives a lot of possible outputs.. and I'm a bit confused for the display= SWR (what iis it? :-D ) and module of impedance. Could you display the sam= e datas as a Smith chart? in this way you could see both resistive and reac= tive parts of the complex impedance changing with frequency which is helpfu= l to understand what is going on. Pictures you shared show SWR vs frequency= and |Z| vs. frequency but shows the R=C2=B1jX form only on one frequency

Marco, IK1HSS

----Messaggio originale----
Da: luis@vigilant.es
Data: 30-ott-2018 12.23
A: "rsgb_lf_group@blacksheep.org"<rsgb_lf_group@blacksheep.org>
Ogg: RE: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5D= OM received)

Hi Marco, = LF

 = ;

The pipe runs inside the building in a narrow space. You are right, it= is preserved from rain and there should be no effect at all

It has been working nice in MF so far, and also first tests in LF were= very succesful. Last year I could even make a QRSS QSO with

9A3KB using the Ropex PA with minor modifications

 

Many variables here. I will rechek connection to the top section of th= e pipe, which may be failing. And then dropping the wire

parallel to the pipe if possible. We have a long weekend ahead which c= an be ideal for this activities =E2=80=A6. at limit ;-)

 

>> My new 2nd DC receiver for MF is = in service since a full day so for some time I'll listen to MF wspr, see you later on LF

 

More rain here today and antenna wires are down. But sourprisingly I c= ould not get RF current yesterday even with low impedance

Time to recheck PA with dummy load. May be I have a failure there too L

 

Oscar, LU1DOW had a fantastic night yesterday in MF. Spots from the St= ates and again LA2XPA

May be he can try to send an EbNaut message and check if we can finall= y receive him in central and south EU

 

73 de Luis

EA5DOM

 

De: ow= ner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org= ] En nombre de marcocadeddu@tin.it
Enviado el: lunes, 29 de octubre de 2018 17:52
Para: rsgb_lf_group@blacksheep.org
Asunto: R: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490= Hz: EA5DOM received)

 

Hi Luis,

while I wish to thank Jay for the nice papers about ERP evaluation, whish t= o ask you a bit more info concerning the change of impedance.

I understand that is not easy to access all "common parts" which often beca= me "everybody away from it!" I guess it should be feasible to drop a thin, = light wire from the top of the building till ground level for a short time = a take some measure to compare with your actual ground.
In this way you should be able to understand if your water pipe is similar = or not to the wire (I'm speaking just to measure with a VNA or your analyze= r not to transmit high power which could be an hazard for people touching t= he momentary dropped wire).
It is nice to read that you have seen the pipe junction bypassed from a str= ip: pipes have usually flanges to joint the sections ore threated ends, in = both cases the use of seals can interrupt the ground continuity: by the way= I suppose that for possible estinguish use, in the reservoir there is sweet water (maybe not drinkable but not se= a water!) and therefore the electrical continuity is granted from the steel= of the pipe and the ground strips not from water! water with low content o= f salts is almost an insulator rather than a conductor!
If you have access to the pipe, you could drop the wire there and measure t= he dc resistance of the pipe against your wire, in the mean time I suggest = to check all those stripes even if I cannot understand why a bad contact on= one of the stripe could be rain sensitive... but I guess it is worth to do ;-)

My new 2nd DC receiver for MF is in service since a full day so for some ti= me I'll listen to MF wspr, see you later on LF

Marco, IK1HSS

----Messaggio originale----
Da: luis@vigilant.es
Data: 28-ott-2018 14.15
A: "rsgb_lf_group@blackshee= p.org"<rsgb_lf_group= @blacksheep.org>
Ogg: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM r= eceived)

Hi Markus, LF

 

The pipe contains presurized water for t= he fire extinguish system. Is a "wet colum" system. Pipe segments

are connected with big brass links. Shou= ld be a good enought current conductor. Down in the basement it<= /span>

connects with a pressure pump and a wate= r reservoir tank, linked to the water grid system

 

Will have to check the ground connection= s of all this stuff when possible. Not easy

But after all, we are all doing all= this "not easy" things because it is not easy to work low bands, right? ;-= )

 

Tested mains ground connection too and i= t helps a lot, but still depends on rain. Access to the ground line at=

the lifts engines room on top building i= s complicated too, as I have no access there because of a AMHPS <= /o:p>

(Anti Mad Ham Protection System) hi, hi<= o:p>

 

Installing my own ground line may be an = option, but using light cable. As I can only support the 80m cable

at the top end, so weight must be low. F= inally may be the best way to go

 

73 de Luis

EA5DOM

 

De: owner-rsgb_lf_group@b= lacksheep.org [owner-rsgb_lf_group@blacksheep.org] en nombre de Markus = Vester [markusvester@aol.com]
Enviado: domingo, 28 de octubre de 2018 0:21
Para: rsgb_lf_group@= blacksheep.org
Asunto: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz= : EA5DOM received)

> Something gets wet in the basement a= nd the pipe gets a better connection to ground, or at least to the water gr= id pipes, which finally run underground


Ah that must be the reason! That drain pipe is obviously not continuou= s metal but inrterropted by some insulating joints or plastic sec= tions, which are more or less bypassed by a water film or fl= ow when it rains.

Could you try to use another ground connection which is continuous all the = way down? E.g. external lightning protection conductors, or even the protec= tive earth in your appartment?

Best 73,
Markus

-----Urspr=C3=BCngliche Mitteilung-----
Von: VIGILANT Luis Fern=C3=A1ndez <l= uis@vigilant.es>
An: rsgb_lf_group@blackshee= p.org <rsgb_lf_group= @blacksheep.org>
Verschickt: Sa, 27. Okt 2018 23:17
Betreff: Re: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5D= OM received)

Hi All, LF

 

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

 

As Marco explained, our setup is not the= usual at ground level in a property plot. And in my case ther ground<= /o:p>

is 80m away down from the feed point, co= il and capacitive topload.

 

Measured with the antenna analyzer I can= see a drop in the impedance module when all gets wet by rain

It is not only an increase of RF current= . Today I measured resistance from the ground side of the feed point

trought the pipe to building basement an= d then returning via the water grid connecting the other side of the

multimeter to a water pipe in my house:<= o:p>

 

4 Ohm measured early morning when it sta= rted with soft rain. At noon we had stronger rain and in the afternoon=

I measured again. It dropped to 2 Ohm. B= ig difference. Something gets wet in the basement and the pipe gets

a better connection to ground, or at lea= st to the water grid pipes, which finally run underground=

 

The top of the antenna is dismantled dur= ing storms, so can't measure impedance with the analyzer right now

but bet it is now well under 30 Ohm and = would drain a few amps

 

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

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 ri= ses and so the radiated signal. 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 t= hat this is the minimum impedance point. 

 

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

 

Have not tried without LPF. The analyzer= measurements are made directly to antenna. But may be a good idea to<= /o:p>

make them with the LPF inserted and see = what happens

 

73 de Luis

EA5DOM

 

De: owner-rsgb_lf_group@b= lacksheep.org [owner-rsgb_lf_group@blacksheep.org] en nombre de marcocadeddu@tin.it [marcocadedd= u@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 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 ra= in (almost doubles).
But.. Luis, probably assumes the lower impedance basing on the higher curre= nt.
Luis, what kind of LPF have you adopted?
Now I have a T filter with no shunting cap at the input and impedance incre= ases 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 impeda= nce 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 measuremen= t 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: <rsgb_lf_group@blacks= heep.org>
Ogg: Antenna resistance (Re: LF: EbNaut Autodecoder 137490 Hz: EA5DOM recei= ved)

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.


 



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