Re: VLF: carrier at 8270.003

[Riccardo Zoli <riccardozoli80@gmail.com>]

Stefan,

congrats, your protection system looks really useful and functional.

Now I'm using a linear push-pull PA (2 x IRF260) supplied with 62V and 5.7A max (about 350W input), however I prefer to drive it in full power out (max efficiency), because in linear zone there is a significant heating.

My goal (I hope!) is to implement an automatic loading coil tuning system (like I'm doing in LF/MF) with moving ferrite core inside, controlled by a microprocessor.

73 de Riccardo IW4DXW

2018-04-27 15:06 GMT+02:00 DK7FC <selberdenken@posteo.de>:

Riccardo,

My antenna current plot is at http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF/TX.png
It shows the current antenna current antenna current. But also the safe limit and the ALC level. At night it was colder and the ALC has regulated down the drive amplitude to the PA. Now the sun (yes, Eddie) is shining and due to the heat the core is warmer and the the losses are a bit higher i think. Thus the ALC is clipping at 1.4 (the factor c for regulating the amplitude) and so the current is moving down and up. But the important thing is that it does not become higher than 56 mA! Because this is the maximum voltage the coil can hold. Thus, the coil is protected against overvoltages. At night i allowed the current tto drop up to 5 mA below the target level, below that, an error would be indicated and the system stops TXing after 5x 0.2 seconds... It seems to be very warm today in Heidelberg so i just set the safe limit to -10 mA, to avoid unwanted stopping of the carrier...

With the ALC function you can hold your antenna current constant, for example if rain starts and the antenna gets slightly detuned, the ALC can increase the amplitude and so the current stays constant. It regulates slowly. This is important because if a fault occurrs, that function must be to slow trying to increase the amplitude to make the fault even more extreme. Before it compensated to dropping current due to the fault, it must be indicated as a fault and then tripped. That's the idea of the combined functions... So far it worked well here and there were a few situations where it safed the system! You can simply sleep much better when TXing at night...

73, Stefan

Am 27.04.2018 14:46, schrieb DK7FC:

Hello Riccardo,

Looks good. I see you know how to set things up.

73 from JO33UC14
Stefan



Am 27.04.2018 09:45, schrieb Riccardo Zoli:

Hi VLF,

Stefan and Paul, many thanks for reports.

Ok, Stefan, great! I'm on air again (in this moment with 620 mA) testing a configuration based on your suggestions.

I made a simple watch plot with antenna current and phase correction (the antenna is now a little shacked, it's a quite windy day here), but I have to optimize the protection statements.

A screenshot of SpecLab attached.

Have a good day

73 de Riccardo IW4DXW

Il Gio 26 Apr 2018, 17:54 DK7FC <selberdenken@posteo.de> ha scritto:

Hi Riccardo,

Your signal is well visible here on my grabber http://www.iup.uni-heidelberg.de/schaefer_vlf/DK7FC_VLF_Grabber2.html

Am 26.04.2018 13:04, schrieb Riccardo Zoli:

Hi VLF,

A new carrier test is running with about 610mA.

Now, with last SL version, the PLL configuration made by Markus seems to works well here, the phase is stable. I started this test yesterday at about 10:00 UTC.

I'm looking for an adequate conditional statement that permits to inhibit the audio (and the TX) in case of an excess of antenna current drop. Any suggestion?

Yes, sure, this is what i'm using all the time here.
First you need to calculate the antenna current from the signal level

I use: s=1820*(10^((peak_a((sgf-10),(sgf+10)))/20))
s= antenna current in mA
sgf=transmit frequency (signal generator frequency)
1820 is just a calibration factor to calibrate the value to mA.
The If condition is 1, so it is executed on each FFT, which means each 200 ms.
Then i define a traget current with the parameter d: d=600 (for example)
Next i define a current limit L, say 100 mA
Now if the actual current s drops L mA below the target value d, then another parameter e, which is a counter level, is increased.
After 200 ms the measurements are repeated and if the current is still to low, e is increased again.
Oh and there is another parameter c, which regulates the output amplitude.
If e exceeds a certain value (i choose 5), the c is set to 0, so the output amplitude becomes 0.

Actually the complete procedure is much more complex, i just described the safety function.
If you like, i can send you a usr file for TXing carriers and EbNaut...

73, Stefan

My current VLF condx attached.

All the best

73 de Riccardo IW4DXW