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Re: ULF: Finally 100 mA on 2.97 kHz

To: [email protected]
Subject: Re: ULF: Finally 100 mA on 2.97 kHz
From: DK7FC <[email protected]>
Date: Tue, 06 Dec 2016 18:37:44 +0100
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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
--


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