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Re: [Discuss-gnuradio] Tuning in VLF with a sound card

From: Marcus D. Leech
Subject: Re: [Discuss-gnuradio] Tuning in VLF with a sound card
Date: Wed, 15 May 2019 17:47:17 -0400
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0

On 05/15/2019 05:45 PM, Glen I Langston wrote:
Hi Marcus,

That’s great.  What could you hear/detect with the 90 kHz bandwidth?

I used it strictly for SIDs in the VLF band up to 40kHz or so...

I had a loop antenna, about 1.2m diameter, and about 10 windings of #20ga wire. No tuning capacitor.

On May 15, 2019, at 5:28 PM, Marcus D. Leech <address@hidden> wrote:

On 05/15/2019 03:23 PM, Brad Hein wrote:
Great suggestion thank you! This also gives me new topics to read up on as I am 
still a VLF amateur.

[Sent from mobile device]
I used a Berhringer "mini-MIC" microphone amplifier, which has a balanced, XLR, 
input, and has bandwidth out to
   about 90kHz.  Worked a champ.  Not as cheap as a DIY op-amp+transformer 
approach, but more convenient,
   to be sure.

On Wed, May 15, 2019, 1:20 PM John Coppens <address@hidden wrote:
On Thu, 2 May 2019 16:22:24 -0400
Brad Hein <address@hidden> wrote:

I took a Raspberry Pi and attached a 48KHz USB sound card, with a big
magnetic loop antenna fed into the mic.
Just a suggestion: If you have a loop antenna, which is a symmetrical antenna,
and couple it to an asymmetrical input (MIC), you will make the antenna
more sensitive to static noise. I'd suggest you use either a transformer or
an 'instrumentation amplifier' with an operational amplifier to convert
the signal from the antenna to asymmetrical signal.

A transformer would be easiest to install at the base of the antenna (no
need for a supply). The op-amp amplifier would cover a larger bandwidth.
(it would also offer some protection for your computer).


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