Re: LF: Re: 23:35 477 EA5DOM de EB3FRN Op8 Deep Search -36 dB1489.0 Hz

[DK7FC <selberdenken@posteo.de>]

Hi Luis,

Am 30.09.2015 14:44, schrieb VIGILANT Luis Fernández:

Hi Stefan, MF

 

I have been calculating the loop area with the help of Google Earth. Not a regular shape but counting on the known perimeter

and measures it can be estimated as 224 m2

 

I detect the RF current with this circuit from G4HUP but have not calibrated it

http://g4hup.com/RFC/RF%20Current%20Meter%20Kit%20V2_0.pdf

I don't use the meter and R3, VR1, VR2 and directly wire down the shack the output from rectifier diode and use an analog

voltmeter. The transformer is made in the same way with a ferrite clamp over loop wire and 10 turns as secondary

The 2x100R load was using 1/2w resistors and burned out when using the PA. So changed them to 2x5W resistors

On the volmeter I can get 60V dc when the antenna is tuned (minimum PA DC current). The 5W resistors still stand !

Minimum PA DC current? Not maximum? 60V DC at 50 Ohm across 2x 5W resistors? I think i do misunderstand something.
Hm, maybe it's better to use 40 turns secondary instead of 10. No need to waste power :-)
In a loop there are of course much higher currents then in a vertical antenna...

 

I'm using 800pF fixed caps and 490pF variable at about mid value to resonate the loop. Bandwith is sharp but lets me work

WSPR and Opera. So lets assume 3KHz

 

Have changed some parameters in Andy's Excel. Sized it down as a 17m diameter loop to match 224m2 loop area

Power down to 75W which is what I get with PA under 50ohm. Conductor diameter 5mm, not 6mm (great difference)

And it reports 1dBW ERP with 11A and 2904V

 

Can it be that high ?

No. 1 dBW is 1.26 W. This is not possible with such a loop and 75W. And this is why i personally prefer to avoid simulations and do measurements instead, during transmitting at that time. :-)

73, Stefan

Probably less due to mismatch in the feeding transformer

 

Nice ERP but in the wrong direction, I'm afraid :(

 

73 de Luis

EA5DOM 

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De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de DK7FC
Enviado el: miércoles, 30 de septiembre de 2015 13:25
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: Re: 23:35 477 EA5DOM de EB3FRN Op8 Deep Search -36 dB1489.0 Hz

Hi Luis.

What is the loop RF current and the loop area? Do you know it?
Is it problematic to match the loop? You just need a C and a ferrite transformer. If you have such a relatively high perimeter, you probably need about 1 nF to resonate it? Currents may be in the range of 10A at 100W? A bandwidth of maybe 3 kHz?

73, Stefan

Am 30.09.2015 11:14, schrieb VIGILANT Luis Fernández:

Hi MF

 

Probably not 2mW ERP Stefan ;-)

 

Have to reconfigure my U3 but really don't know which ERP I'm getting right now

The PA outputs 60V RMS under 50Ohm load, but the loop is not an ideal load and I can tune it

to about 80V RMS. When detuned, RMS runs up to >>100V and PA gets into problems

 

I tried to get loop performance using Andy G4JNT excel and this is what I got

https://dl.dropboxusercontent.com/u/7162072/Fotos%20varias/MF/70m%20MF%20Loop%20at%20100W%20.png

 

Probably many things wrong there

What I use is a 70m perimeter loop made from RG59 coax (braid and inner shorted on ends) but not a round circle

The resonate cap is very close to what I need to tuneit. So the "equivalent" round loop diameter should be 21m 

Go figure ! :-)

 

One detail to mention:

Yesterday, it rained. Not very usual here and still not tested the loop with this Tx power and with wet terrace

It seems to me that my signals was better than before. Could the wet terrace worked as a kind of reflector or

re-shapped the radiation diagram of the horizontal loop making it more efficient for Dx ??

 

The loop is not equidistant from terrace but keeps about 3 to 4 meter high, and just 1m on the feeding point

 

73 de Luis

EA5DOM

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De: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacksheep.org] En nombre de DK7FC
Enviado el: miércoles, 30 de septiembre de 2015 10:18
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: Re: 23:35 477 EA5DOM de EB3FRN Op8 Deep Search -36 dB1489.0 Hz

Hi Luis,

Ooh, very well! I'm glad that i received you the first time! Is it really 2 mW ERP?
Oh and BTW it was in WSPR, the super mode!!!! ;-)

73, Stefan

Am 30.09.2015 00:17, schrieb VIGILANT Luis Fernández:

Even with the loop we are on the way ;-)

2015-09-29 22:00

EA5DOM

0.475611

-27

0

IM98wn

0.002

DK7FC/P

JN49ik

1398

27

73 de Luis

EA5DOM

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De: owner-rsgb_lf_group@blacksheep.org [owner-rsgb_lf_group@blacksheep.org] en nombre de DK7FC [selberdenken@posteo.de]
Enviado: lunes, 28 de septiembre de 2015 21:47
Para: rsgb_lf_group@blacksheep.org
Asunto: Re: LF: Re: 23:35 477 EA5DOM de EB3FRN Op8 Deep Search -36 dB1489.0 Hz

Am 28.09.2015 17:02, schrieb VIGILANT Luis Fernández:

[...]

 

Next in the list is going vertical. Coil and variometer on the way. Keep tuned ;-)

 

73 de Luis

EA5DOM

Oh yes! Do it!!! :-) Looking forward to a QSO :-)

73, Stefan