```Hello Stefan, my calculations assume that you are using a single turn loop. 73, Rik ON7YD ________________________________________ Van: [email protected] <[email protected]> namens DK7FC <[email protected]> Verzonden: vrijdag 25 januari 2019 19:02 Aan: [email protected] 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: [email protected]<[email protected]> > namens DK7FC<[email protected]> > Verzonden: vrijdag 25 januari 2019 15:23 > Aan: [email protected] > 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 > > > ```