Message-ID: <5C4B5A8E.2000804@posteo.de>
Date: Fri, 25 Jan 2019 19:50:54 +0100
From: DK7FC <selberdenken@posteo.de>
User-Agent: Mozilla/5.0 (Windows; U; Windows NT 6.1; de; rv:1.9.1.8) Gecko/20100227 Thunderbird/3.0.3
MIME-Version: 1.0
To: rsgb_lf_group@blacksheep.org
References: <D98C1CCC49324084BCF225E22F521809@DELL4> <1UTCTNxG9H.5T3bfQF3xD0@optiplex980-pc> <9C9C8088-AD45-4DDF-BD7E-66D13F0D835C@md.metrocast.net> <CANA3B6VBpQ0G92wmOniO3GvedBbaOoBuMuFPW1Fs743B8VCvpw@mail.gmail.com>,<5C4B1BD5.6010404@posteo.de> <1548429783635.69862@kuleuven.be>,<5C4B4F2A.6000201@posteo.de> <1548440122358.46919@kuleuven.be>
In-Reply-To: <1548440122358.46919@kuleuven.be>
Subject: Re: LF: Re: TXing WSPR/MF on an indoor loop
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hi Rik,

I am using a single turn loop. Just the primary winding of the matching 
transformer has 9 turns. So the impedance is 81 times higher than the 
loss resistance of the loop.

73, Stefan

Am 25.01.2019 19:15, schrieb Rik Strobbe:
> Hello Stefan,
>
> my calculations assume that you are using a single turn loop.
>
> 73, Rik  ON7YD
>
>
> ________________________________________
> Van: owner-rsgb_lf_group@blacksheep.org<owner-rsgb_lf_group@blacksheep.org>  namens DK7FC<selberdenken@posteo.de>
> Verzonden: vrijdag 25 januari 2019 19:02
> Aan: rsgb_lf_group@blacksheep.org
> Onderwerp: Re: LF: Re: TXing WSPR/MF on an indoor loop
>
> Hello Rik,
>
> Thanks for your calculations. Looks like the 1000 km distance is already
> done.
> Of course i also matched the loop. It uses a small blue ferrite core
> with just 20mm diameter. The big RF litz (DECCA litz with 729 strands
> (3*3*3*3*3*3) passes just one time through the core, and then 9 turns on
> the primary side, so this is much closer to 50 Ohm ;-)
> I can measure the antenna current on the primary side, 1.6 A. So it must
> be 9 times higher in the loop...
>
> 73, Stefan
>
> Am 25.01.2019 16:23, schrieb Rik Strobbe:
>    
>> Hi Stefan,
>>
>> the radiation resistance of a small loop: Ra = (320*Pi^4*A^2)/lambda^4 where A is the loop area in m^2
>> So for lambda = 630 m and A = 4 m^2 the radiation restistance Ra = 3.17 µOhm (micro Ohm).
>> At least in theory, an indoor antenna will probably have some extra losses.
>> The gain of a small loop is -0.39dBd = 0.9
>>
>> So the theoretical ERP = 0.9*14^2*3.17e-6 = 0.56 mW = -32.5dBW
>>
>> Will I be able to copy you?
>> Your regular 1W ERP signal is often up to +15dB here in WSPR, so the 0.56 mW should peak 15-32= -17dB. That's a solid copy in WSPR!
>> Even with 10dB additional loss I should be able to copy you.
>>
>> Did you just resonate the loop or also matched it?
>> Based on 40W RF power (50W DC at 80% efficiency) and 14A antenna current the antenna impedance is only 0.2 Ohm. That would result in a VSWR of 250 (!) for 50 Ohm TX output impedance.
>>
>> 73, Rik  ON7YD - OR7T
>>
>> PS= I hope you have a wooden bed (and bedsprings)
>>
>> ________________________________________
>> Van: owner-rsgb_lf_group@blacksheep.org<owner-rsgb_lf_group@blacksheep.org>   namens DK7FC<selberdenken@posteo.de>
>> Verzonden: vrijdag 25 januari 2019 15:23
>> Aan: rsgb_lf_group@blacksheep.org
>> Onderwerp: LF: TXing WSPR/MF on an indoor loop
>>
>> Hi MF,
>>
>> A few days ago i took some RF litz wire and built a loop that is now
>> hanging on the wall inside my home, just 1m besides the bed :-) (no XYL
>> here spoiling the fun). The loop is beaming to about 150/330 deg.
>>
>> After playing some days on 160m (an unusual high frequency, witch feels
>> very strange. And the band is full of unknown callsigns!!) i did now
>> move down to more or less low frequencies, the 630m band!
>>
>> About 10 nF is needed to series resonate the loop. It has about 2m x 2m
>> of size. The antenna current is not stable because the WIMA FKP-1
>> capacitor becomes warm during the 2 minute WSPR sequence. But the
>> maximum current in the loop is 14 A. That explains why the cap becomes
>> warm. A small parallel variable capacitor tunes to resonance. It is
>> tuned so that the upheating capacitor runs into the resonance point in
>> the middle of the WSPR sequence, then it runs out of the resonance by
>> upheating further. It can cool down during the following quiet periods..
>>
>> 14A into a 4 square meter loop at 475.7 kHz, how much ERP is that? The
>> PA consumes about 3.5 A at 13.8V, i.e. about 50 W.
>>
>> The system will run over the weekend, even during daylight. The signal
>> generator is a Raspi which will have no internet connectivity from now
>> on, so let's hope the time offset stays inside the accepted range for
>> this experiment.
>>
>> What will the best distance be? So far the band is closed but i'm
>> optimistic to crack the 1000 km distance with this QRP setup.
>>
>> 73, Stefan
>>
>>
>>
>>      
>
>