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Content preview: Hi Stefan, Luis Luis pointed out changes in impedance from 30 to 100 ohms not 1000 ;-) Leaving this misreading away, you are right Stefan: it should be nice to know what happen to both reactive and re [...] 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 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 X-Scan-Signature: 611f9af8a0f6ba007b1ec6dce409caf4 Subject: R: Re: LF: LF daylight test close to the north hemisphere solstice Content-Type: multipart/alternative; boundary="----=_Part_7949_11913225.1561797576811" X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on post.thorcom.com X-Spam-Level: X-Spam-Status: No, hits=0.0 required=5.0 tests=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_7949_11913225.1561797576811 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Hi Stefan, Luis=20 Luis pointed out changes in impedance from 30 to 100 ohms not 1000 ;-) Leaving this misreading away, you are right Stefan: it should be nice to kn= ow what happen to both reactive and resistive component of the impedance. I assume that Luis has still working a variometer thus he can manage change= of reactance with it and change of resistance with an insulating and match= ing transformer Marco, IK1HSS ----Messaggio originale---- Da: selberdenken@posteo.de Data: 29-giu-2019 10.21 A: Ogg: Re: LF: LF daylight test close to the north hemisphere solstice Hi Luis, Am 28.06.2019 22:04, schrieb VIGILANT Luis Fern=C3=A1ndez: > My problem is that the antenna impedance varies a lot with humidity. This= days we have a hot and > dry weather about 30% moisture. VNA shows an impedance value of just 30Oh= ms at resonance > Previous week having sea moisture with 80% values, which are normal here = over summer, the > impedance rised to 100Ohm at resonance. Of course, PA works in a complete= ly different way in both > cases. What happens with the reactive part of the impedance? Does it stay=20 constant or do you have to retune all the time? Then, the relays and=20 tapped transformer wouldn't help you. > The best antenna impedance is about 70 Ohm, were I can get 3.2A RF curren= t with 15A@33V PA current > Higer impedance causes PA current to rise and RF current drops. Mosfets a= lso get much hotter > Low antena impedance produces high RF currents but low PA current and so,= less power > and higer voltages in the LPF which causes arcs. (LPF is also pending res= ize. Is the only part still > remaining from the old Ropex PA) > =20 Hmmmm, hard to belive that it is just the humidity that leads to a=20 variation from 70 to 1000 Ohm. Maybe it is a bad ground contact at some=20 point? You could do a test: Tune to resonance when the system is at 70 Ohm.=20 Then run low power, maybe 5W. Run a carrier transmission for some days.=20 Observe the signal level at your remote site in 7 km distance. Use=20 SpecLabs plotter and plot the signal level over time. Watch the=20 variations. When the system changes slowly to 1000 Ohm, the antenna=20 current will drop and so the signal will be lower. If this happens=20 slowly, when it starts to rain, then it is ok. But maybe you will find a=20 sudden jump of the current, then it could be a bad contact somewhere.=20 You know what i mean? > So, I need a matching transformer, but must be variable and remotely sele= ctable. May be selecting > taps with a set of relays or any other mechanical selector. What do you p= ropose for that ? > =20 It is all possible but you will need time again! ;-) > How many turns ? I have a pair of the big blue cores you recommended > =20 Which ones? The very big ones? I used 18 turns primary for 50 Ohm.=20 Calculate the voltage at 50 Ohm and your power level. Then apply this=20 voltage to the core and the primary winding only, without a load. The=20 core should stay cool! Or, if you don't have a voltage source, build a=20 1:1 (18:18) transformer and apply full power through it and connect a=20 dummy load. The transformer should stay cool. If you want to transform from 50 to 1000 Ohm (which is not a good=20 solution somehow) then the secondary winding needs 18*sqrt(1000/50) =3D 80= =20 turns. I would focus on finding the reason for the heavy changes. I would doubt=20 that it is just humidity, although i would certainly expect that=20 humidity has a significant influence in your configuration. Relays: I personally would select such one:=20 https://www.reichelt.de/steck-printrelais-1-co-16-a-12-v-dc-sensitiv-fin-40= -61-7-12v-p259198.html?&trstct=3Dpos_12 73, Stefan > 73 de Luis > EA5DOM > > > ________________________________________ > De: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.or= g] en nombre de DK7FC [selberdenken@posteo.de] > Enviado: mi=C3=A9rcoles, 5 de junio de 2019 8:16 > Para: rsgb_lf_group@blacksheep.org > Asunto: Re: LF: LF daylight test close to the north hemisphere solstice > > Hi Luis, > > No, i just mean a second transformer between PA and the other > transformer, into the coax line. A simple 1:1 ferrite transformer. > Your ground conductors into and arround the building are a part of the > antenna, obviously causing a high voltage between that ground and your > shack ground. All you can do is reducing the coupling impedance > (capacitive) and the electrical field strength. A well dimensioned 1:1 > transformer will provide a good decoupling and low losses. The improved > decoupling may change the resonance a bit (because your shack earth is > less a part of the system taking RF currents), so a retuning is > required. Hopefully your shack earth is not the dominant part of the > antenna ground :-) The less it is a part of the ground system, the less > is the detuning of the antenna when inserting the second transformer. > > 73, Stefan > > > =20 ------=_Part_7949_11913225.1561797576811 Content-Type: text/html;charset="UTF-8" Content-Transfer-Encoding: quoted-printable Hi Stefan, Luis
Luis pointed out changes in impedance from 30 to 100 oh= ms not 1000 ;-)
Leaving this misreading away, you are right Stefan: it s= hould be nice to know what happen to both reactive and resistive component = of the impedance.
I assume that Luis has still working a variometer thus= he can manage change of reactance with it and change of resistance with an= insulating and matching transformer

Marco, IK1HSS

----Messaggio originale----
Da: selberdenken@posteo.de
Data: 29-giu-2= 019 10.21
A: <rsgb_lf_group@blacksheep.org>
Ogg: Re: LF: LF day= light test close to the north hemisphere solstice

Hi Luis,

Am= 28.06.2019 22:04, schrieb VIGILANT Luis Fern=C3=A1ndez:
> My problem= is that the antenna impedance varies a lot with humidity. This days we hav= e a hot and
> dry weather about 30% moisture. VNA shows an impedance = value of just 30Ohms at resonance
> Previous week having sea moisture= with 80% values, which are normal here over summer, the
> impedance = rised to 100Ohm at resonance. Of course, PA works in a completely different= way in both
> cases.
What happens with the reactive part of the i= mpedance? Does it stay
constant or do you have to retune all the time? = Then, the relays and
tapped transformer wouldn't help you.
> The = best antenna impedance is about 70 Ohm, were I can get 3.2A RF current with= 15A@33V PA current
> Higer impedance causes PA current to rise and R= F current drops. Mosfets also get much hotter
> Low antena impedance = produces high RF currents but low PA current and so, less power
> and= higer voltages in the LPF which causes arcs. (LPF is also pending resize. = Is the only part still
> remaining from the old Ropex PA)
>&nbs= p;  
Hmmmm, hard to belive that it is just the humidity that = leads to a
variation from 70 to 1000 Ohm. Maybe it is a bad ground cont= act at some
point?

You could do a test: Tune to resonance when t= he system is at 70 Ohm.
Then run low power, maybe 5W. Run a carrier tra= nsmission for some days.
Observe the signal level at your remote site i= n 7 km distance. Use
SpecLabs plotter and plot the signal level over ti= me. Watch the
variations. When the system changes slowly to 1000 Ohm, t= he antenna
current will drop and so the signal will be lower. If this h= appens
slowly, when it starts to rain, then it is ok. But maybe you wil= l find a
sudden jump of the current, then it could be a bad contact som= ewhere.
You know what i mean?

> So, I need a matching transfo= rmer, but must be variable and remotely selectable. May be selecting
>= ; taps with a set of relays or any other mechanical selector. What do you p= ropose for that ?
>   
It is all possible but you = will need time again! ;-)
> How many turns ? I have a pair of the big= blue cores you recommended
>   
Which ones? The v= ery big ones? I used 18 turns primary for 50 Ohm.
Calculate the voltage= at 50 Ohm and your power level. Then apply this
voltage to the core an= d the primary winding only, without a load. The
core should stay cool! = Or, if you don't have a voltage source, build a
1:1 (18:18) transformer= and apply full power through it and connect a
dummy load. The transfor= mer should stay cool.
If you want to transform from 50 to 1000 Ohm (whic= h is not a good
solution somehow) then the secondary winding needs 18*s= qrt(1000/50) =3D 80
turns.

I would focus on finding the reason f= or the heavy changes. I would doubt
that it is just humidity, although = i would certainly expect that
humidity has a significant influence in y= our configuration.

Relays: I personally would select such one:
h= ttps://www.reichelt.de/steck-printrelais-1-co-16-a-12-v-dc-sensitiv-fin-40-= 61-7-12v-p259198.html?&trstct=3Dpos_12

73, Stefan
> 73 de = Luis
> EA5DOM
>
>
> _______________________________= _________
> De: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_gro= up@blacksheep.org] en nombre de DK7FC [selberdenken@posteo.de]
> Envi= ado: mi=C3=A9rcoles, 5 de junio de 2019 8:16
> Para: rsgb_lf_group@bl= acksheep.org
> Asunto: Re: LF: LF daylight test close to the north he= misphere solstice
>
> Hi Luis,
>
> No, i just mean = a second transformer between PA and the other
> transformer, into the= coax line. A simple 1:1 ferrite transformer.
> Your ground conductor= s into and arround the building are a part of the
> antenna, obviousl= y causing a high voltage between that ground and your
> shack ground.= All you can do is reducing the coupling impedance
> (capacitive) and= the electrical field strength. A well dimensioned 1:1
> transformer = will provide a good decoupling and low losses. The improved
> decoupl= ing may change the resonance a bit (because your shack earth is
> les= s a part of the system taking RF currents), so a retuning is
> requir= ed. Hopefully your shack earth is not the dominant part of the
> ante= nna ground :-) The less it is a part of the ground system, the less
>= is the detuning of the antenna when inserting the second transformer.
&= gt;
> 73, Stefan
>
>
>   


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