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Message-ID: <D8460B0A34AE404DB2D6BFBD17806C79@JimPC>
From: "James Moritz" <james.moritz@btopenworld.com>
To: <rsgb_lf_group@blacksheep.org>
References: <BDEMKFCNLMIILGIFNONNEEOADOAA.victor13@online.nl> <4E5FBC79.4060902@legal-medicine.de>
In-Reply-To: <4E5FBC79.4060902@legal-medicine.de>
Date: Thu, 1 Sep 2011 23:08:35 +0100
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Subject: Re: LF: Re: Ferrite wideband antennas?
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Dear Peter, Victor, LF Group,

Thanks for the info... unfortunately the wide-band type of loop is not 
really viable at my QTH due to the 10s of volts/metre from the nearby 
broadcast stations.

>> try a BFP640,rBB 1ohm.Noise as low as 300pV/sqrt(Hz) is possible.Very
>> cheap,but one drawback,Ft is about 40GHz,not easy to get stable.For 
>> topband
>> I use BD139 (yes a lf driver),rbb 1,2 Ohm,very easy to use..

For my 136k and 500k "bandpass loops" preamps, I have used the ZTX690B. The 
complete preamp circuit with the input shorted gives an equivalent input 
voltage noise of about 600pV/sqrt Hz. The feedback and bias resistors must 
contribute significantly to this, so the transistor itself is certainly 
lower noise still. It is characterised as a small power switch, with high 
current rating, low saturation voltage and minimum hFE of 500 - transistors 
of this general type seem to be good choices for LF/MF low-impedance 
preamps. The fT is "150MHz minimum", so UHF instability is not a problem.

Cheers, Jim Moritz
73 de M0BMU