Message-ID: <001b01cc6639$caf90c30$0401a8c0@xphd97xgq27nyf>
From: "mal hamilton" <g3kevmal@talktalk.net>
To: <rsgb_lf_group@blacksheep.org>
References: <7B6D5F6A8CEE4E3CAB04E35F1F9E9732@JimPC>
Date: Mon, 29 Aug 2011 11:52:48 +0100
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Subject: LF: Re: Ferrite rod antenna - on-air testing
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This looks encouraging Jim for the ferrite rod/antenna approach.
What value uH inductance es C  did u need to resonate on 137. I wonder how
good it might be on the long haul DX compared to the loops that you use or
even larger inv L antennas.
I am getting results with a ferrite bunch rods(9) and a suitable C to
resonate but without a preamp the signals are well down, however it is
inducing some voltage into the RX.When I get time I will build a preamp.
I expect there are limitations but never the less a useful antenna.

mal/g3kev

----- Original Message -----
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, August 28, 2011 7:44 PM
Subject: LF: Ferrite rod antenna - on-air testing


> Dear LF Group,
>
> The QRN level on 136kHz has finally died away, and I was able to record
the
> attached spectrogram, showing DK7FC calling CQ around 1755utc, using my
> prototype ferrite rod antenna. On the left of the spectrogram, the rod is
> oriented for N-S reception, and the background noise consists mainly of
> horizontal Loran spectral lines, plus some unidentified, low-level,  local
> "mush". On the right of the spectrogram, Stefan's signal level increases
as
> the rod is rotated for E-W reception. Here, the noise level is mainly
> vertical streaks due to sidebands of DCF39's FSK modulation. The black
area
> at the right hand edge of the screenshot is where the ferrite rod was
> replaced by a "dummy antenna" inductor, and shows that the internal noise
> level of antenna and preamp is below the band noise level (by around
10dB).
>
> The band noise seen with the ferrite rod is practically the same as seen
> with larger loop antennas under quiet conditions, so this practical test
> does show that a reasonably compact ferrite rod can give sensitivity
limited
> only by the external band noise on 136k. In fact, there is some margin for
> making the rod smaller still in this case.
>
> BTW, Stefan was an S4 audible signal - CW would have been a bit difficult
> due to the bursts of noise from DCF39, but a QSO would certainly be
> possible, especially if a quieter frequency were chosen.
>
> Cheers, Jim Moritz
> 73 de M0BMU
>