Re: VLF: 3 carriers near 5170 Hz

[DK7FC <selberdenken@posteo.de>]

Hi Markus,

Just genial! I didn't think about this option.
Also it is a bit harder to understand why it should be 90 deg.

Now, i just restarted the 3 carriers and played with that option:
In the attachment you can see the 3 carriers.
At 8:29 UTC the ALC tuned all 3 carriers to the target current of 120 mA. This is the maximum current possible for the 3 carriers, as long as the phase of all 3 carriers is 0.
At 8:30:20 UTC i switched the phase of 5130.005 Hz carrier  by 90 deg. The PA then seems to be farer away from clipping, so a lower ALC level is required for the 3 carriers. Thus the currents jumped to a higher value and were regulated back to the target current after some time.
At 8:32 UTC i switched the phase back to 0. Then the ALC levels were to low and were regulated back to the level as of 8:29 UTC.
Now at arround 8:36 UTC i changed the target antenna current to 135 mA and let the phase at 0. The ALC tries to rise the level until the new target antenna current is reached (there is a maximum ALC level where it stops then). However the PA is now clipping and it is not possible to reach that target level. I already knew that. That's why i choose 120 mA yesterday.
At 8:38 UTC i switched the phase of the central carrier by 90 deg again. You see what happens. After some time the levels are meeting arround 135 mA which was not possible before!
I changed the levels to 140 mA now. This level works stable here and there is some tuning range left, in case that the resonance moves a bit...

So thanks for the suggestion! The signal is now 1.3 dB stronger. So, since 9:20 UTC the carriers are back at 140 mA. I will run them for some hours and tell the end of the transmission later.

I'll put a narrow band spectrogram on the central carrier, to check if the splitting problem still exists...

73, Stefan



Am 27.10.2017 22:40, schrieb Markus Vester:

Hi Stefan,

with three carriers, you can minimize the peak-to-average ratio by optimizing relative phases. When all three are in equi-phase, the maximum voltage will be 3 times that of a single carrier (+9.54 dB). Shifting the central carrier by 90° will bring that down to sqrt(5) = 6.99 dB. Thus at same given PEP, 2.55 dB can be gained.

No idea why the middle line could have split up.

Best 73,
Markus  
  


-----Ursprüngliche Mitteilung-----
Von: DK7FC <selberdenken@posteo.de>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 27. Okt 2017 20:51
Betreff: Re: VLF: 3 carriers near 5170 Hz

Hi Paul,

oops, that is strange. Maybe the PA is a bit nonlinear (slightly
clipping) and the measurement is mixed up. I will try to solve that.
Well the difference between 5090 and 5170 seems not to be very much.
Would it makes sense to repeat the experiment? Tomorrow i could run it
for a longer time, e.g. 6 hours. Then there should be usable values on
each antenna and frequency.

73, Stefan

Am 27.10.2017 20:03, schrieb Paul Nicholson:
>
> Stefan wrote:
>
> > Since 13:20 UTC im running 120 mA on 3 individual frequencies:
> > 5090.005 Hz | 5130.005 Hz | 5170.005 Hz
>
> > Carriers stopped at 16:20 UTC....
>
> Received in 92.6uHz
>
> H-field (new) E-field
> 5090.005: 9.3 dB 10.38 dB
>
> 5130.005: N/A See below
>
> 5170.005: N/A 10.2 dB
>
> N/A where the signal is too weak to measure.
>
> Something wrong with 5130.005, here's the E-field spectrum
>
> http://abelian.org/vlf/tmp/171027a.gif
>
> --
> Paul Nicholson
> --
>

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