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Re: AW: Re: LF: 8269.990Hz

To: [email protected]
Subject: Re: AW: Re: LF: 8269.990Hz
From: Markus Vester <[email protected]>
Date: Fri, 22 Apr 2016 16:28:06 -0400
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Hi Uwe,
just my five cents worth:
With the big TX antenna you'll have so much RX signal that you won't need to match or even resonate it. You can basically bypass the coil(s) and connect the wire directly to the soundcard, and you may still need some resistive attenuation. What would make sense is
- a transformer to separate antenna ground from computer ground,
- an RC lowpass (eg. 10kohm 5nF) to prevent soundcard overload from strong HF, MF and LF signals, 
- a diode limiter to protect the soundcard from nearby lightning or transmitters,
- perhaps another RC highpass to reduce 50 Hz hum (if the transformer is not already doing that for you).
Here I am using my LF/MF Marconi transmit antenna and connect the VLF soundcard to a 33 nF capacitor in the ground lead  (see attached sketch). The transmit voltage is blocked by a 2.2 mH trap and a diode pair so the circuit can be lkeft in place during transmit sessions. Alternatively when it is raining and none of the TX loading coils is in use, the antenna is connected through 10 kohm instead. The 10 mH transformer broadly resonates near 8 kHz, with enough bandwidth (Q ~ 3) to keep ringing short for the noise blanker. As I am using a mono soundcard, the GPS 1pps pulse is resistively added to the RF, and it is later removed by the SpecLab noiseblanker. The pnp emitter-follower was only inserted as a kludge because my particular cheap soundcard produced excessive noise with high source impedances.
Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: uwe-jannsen <[email protected]>
An: rsgb_lf_group <[email protected]>
Verschickt: Fr, 22 Apr 2016 12:24 pm
Betreff: AW: Re: LF: 8269.990Hz

Paul, Markus, Stefan,
thanks for report.
Stefan, any decode?

I come up with the idea of  changing the antenna from TX… to RX…
that means changing the the matching point of from five Ohm to abt five kOhm and
retuning the antenna.
question: should I do so?


Attachment: vlf_rx_coupling.jpg
Description: JPEG image

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