To: | [email protected] |
---|---|
Subject: | Re: LF: RE: 8270.0025 Tuesday Apr 19 |
From: | Markus Vester <[email protected]> |
Date: | Wed, 20 Apr 2016 04:07:11 -0400 |
Dkim-signature: | v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20150623; t=1461139632; bh=mAFyh/PlyV2+DWUi/hokJNX9DaGjYSferVLjrNUGJ8A=; h=From:To:Subject:Message-Id:Date:MIME-Version:Content-Type; b=41nNUEoIqr/dOOwGsl5bHRQsWw85M05bEkcgBCuk/mXII7EeFQ/7G/ghH6aanzZAR S10gJtw5BE3NvVssL/3S8iAS/BZ1cCIcVgFH4F2gU06Gcsq8vm3DRs2R6DFiRx+1Cf RpTNZ3mLRslNyoVsjGhlwjZxQPARJP086qCf03xY= |
In-reply-to: | <[email protected]> |
References: | <[email protected]> |
Reply-to: | [email protected] |
Sender: | [email protected] |
Hi Jim,
the transmit antenna is physically larger: The apex of the topload is at 21 m above ground or 12 m above our rooftop. But the wires are sloping downward at steep angles, and the antenna is partly shielded by surrounding houses and trees. The effective height was measured as 8.7 m at 139 kHz by comparison of received open-circuit voltage versus a small nonresonant loop. I believe that effective height may be about 20% lower at VLF due to more effective shielding from resistive objects, but this difference has not been measured so it's just a guess.
Thanks Paul for the comparison and valuable details regarding spherics blanking.
Jim, any plans for VLF activities from your end? 73, Markus
Von: hvanesce <[email protected]> An: rsgb_lf_group <[email protected]> Verschickt: Di, 19 Apr 2016 11:22 pm Betreff: LF: RE: 8270.0025 Tuesday Apr 19 Markus,
Nice signal!
A question perhaps for Paul or yourself follows:
At ~0.22 fT (estimated from Paul’s spectrogram) I expected to see >> 10dB SNR in 278uHz. 10dB SNR is off scale so I looked at the on/off tails and noise, and I still seemed to be off by a substantial amount in the relationship of flux density and SNR in Paul’s spectrogram, but I had not factored in sferic noise and cancellation.
If I assume 30fT/rt-Hz for sferics, and 20dB sferic noise cancellation in a clipper, then a 0.22fT signal (with 3.0 fT/rt-Hz sferic noise after clipping) would yield roughly 13dB SNR in 278uHz, which seems consistent with Paul’s spectrogram.
My question is:
Is 20dB noise reduction a reasonable estimate for the sferic clipper/blanker?
I think that I had become accustomed over the winter to seeing near-preamp-noise-limited SNR on a number of VLF receivers, notwithstanding sub-fT/rt-Hz preamp noise levels, and that may explain why I was expecting >>10dB SNR for ~0.22fT and noise in 278 uHz. If Paul considers the sferic clipper/blanker noise reduction to be roughly 20dB that would explain my overestimate.
Nice signal from your (9m?) antenna!
73,
Jim AA5BW
From: [email protected] [mailto:[email protected]] On Behalf Of Markus Vester
Sent: Tuesday, April 19, 2016 1:25 PM To: [email protected] Subject: VLF: 8270.0025 Tuesday Apr 19 After a couple of minor modifications (different soundcard, thicker piece of wire from the top of the loading coil), I ran a test carrier from 13:15 to 15:15 UT. I briefly ventured pushing the drive up to 0.42 A (= 30.0 kV rms) with no adverse effects, but then settled to 0.35 A to have a bit of margin for the long transmission. Unfortunately not much appeared in Heidelberg and Breclav in the upcoming afternoon QRN. But then, looking at Paul's spectrogram saved my day:
All the best,
Markus (DF6NM)
|
<Prev in Thread] | Current Thread | [Next in Thread> |
---|---|---|
|
Previous by Date: | Re[2]: LF: Alex (R7NT) reports, Chris Wilson |
---|---|
Next by Date: | LF: LF Receiving (was Alex (R7NT) reports), Mike Dennison |
Previous by Thread: | Re: LF: RE: 8270.0025 Tuesday Apr 19, Paul Nicholson |
Next by Thread: | Re: LF: RE: 8270.0025 Tuesday Apr 19, Paul Nicholson |
Indexes: | [Date] [Thread] [Top] [All Lists] |