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Date: Tue, 06 Dec 2016 18:37:44 +0100
From: DK7FC <selberdenken@posteo.de>
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Subject: Re: ULF: Finally 100 mA on 2.97 kHz
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Hi Paul, ULF,

Most interesting anyway, despite there is no sign of my signal.

Yesterday i build an analog amperemeter for AC measurements and 
calibrated it for a range up to 250 mA at 2970 Hz. I put it series to 
the wire between the cold end of the coil and the output of the 
transformer. Then i adjusted to 100 mA again and went on the roof. To my 
surprise it also showed 70 mA instead of 100 mA!!!!!!!! So that means 
the other one is damaged. I was sure that i calibrated it correctly. I 
dismantled the other one and searched for the fault in the lab (= 
warm!). A bridge rectifier out of 4x UF4007 diodes is used and a 1 Ohm / 
2 Watt resistor on its output. Then another resistor to tune the desired 
range (300 mA) in front of the meter. It turned out that the 1 Ohm 
resistor has 2 Ohms!! It is crazy, it should hold 1.4 A permanently. 
There can be no HV breakdown or so. To control the measurement i applied 
1A and measured 2V...
Next, why doesn't it show 200% when the resistor value is 200%? It spooks!
Now i replaced it by a new 1 Ohm resistor and put a big C in parallel 
(impulse capacitor) and recalibrated the meter. After repeating the test 
with 2 amperemeters in series, they show the same value, on the roof and 
in the shack, as expected.

But all that means a bit more! It means that my power on 6470 Hz has 
been lower during the last tests, just 200 mA instead of 280. But the 
good message is that i can run 3 dB more power now ;-)
It also means that my yesterdays 100 mA carrier has just been a 70 mA 
carrier. 3 dB weaker than expected.
Next i found that i can not achieve 100 mA when tuning up the PA voltage 
which can be 25 V maximum. So i had to modify the inductance of the coil 
so the resonance comes a bit closer to 2970 Hz.
After some testing, a few ferrite cores put into the field were doing a 
great job here to pull the resonance 10 Hz down: 
https://dl.dropboxusercontent.com/u/19882028/ULF/20161206_171409.jpg
Now i can tune to 100 mA and a bit more in this test: 
https://dl.dropboxusercontent.com/u/19882028/ULF/20161206_170930.jpg

Since 16:25 UTC i'm running a carrier again, this time with a real 100 
mA. It will be on air until 19 UTC.

73, Stefan

Am 06.12.2016 11:34, schrieb Paul Nicholson:
>
> Stefan wrote:
>
> > With 70 uOhm radiation resistance the resulting ERP
> > is now entering the microwatt range: 1.2 uW on the
> > 101km band.
>
> I think I should be able to detect 1.2uW without trouble.
>
> Using for example, Wait's 1958 simple field strength
> formula, your 1.2uW should reach Todmorden with
>
>  Day:  50nV/m or 0.17 fT
>
>  Night: 40nV/m or 0.13 fT
>
> Wait's formula gives a fair guess at 8270 Hz signals and is
> in the same ballpark as LWPC.  For example Markus with 10uW
> at 8270 range 1023 km at midday:
>
>  Wait 1958: 0.057 uV/m or 0.188 fT
>  LWPC:  0.053 uV/m or 0.18 fT
>  Rxed sigs: variable 0.05 to 0.12 fT
>
> LWPC doesn't seem to work at 2970 so can't compare.
>
> > A stable carrier at 100 mA was sent from 12:50 UTC to 14:24 UTC.
>
> Noise floor in 177 uHz was 0.03 fT but there is no hint of
> a signal at all.
>
> -- 
> Paul Nicholson
> -- 
>