Message-ID: <001201c4f321$cb453fc0$1201a8c0@uwe>
From: "Uwe Wensauer" <uwe.wensauer@gmx.de>
To: rsgb_lf_group@blacksheep.org
References: <82.1ecc794c.2f0d0993@aol.com> <001b01c4f0bd$9a6f7f20$eb1686d4@erica>
Date: Wed, 5 Jan 2005 13:26:33 +0100
MIME-Version: 1.0
Subject: LF: Re: Re: Pre-amps on LF
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Sender: owner-rsgb_lf_group@blacksheep.org
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org

Hi Peter,
just to start LF.
Could hear some stn but have to improve my RX- sensitivity. (TS930-S or FT-
847)
May be a Pre- amp could improve performance.
Therefore - please send me the diagramm or link to get it

Uwe, DK1KQ


----- Original Message -----
From: "g3ldo" <g3ldo@ukonline.co.uk>
To: <rsgb_lf_group@blacksheep.org>
Sent: Sunday, January 02, 2005 12:23 PM
Subject: LF: Re: Pre-amps on LF


> Dave G0MRF said:
>
> > There have been a number of postings about the poor response of amateur
> > radio receivers on 136kHz.
> >
> > The main reason for this lack of performance is usually the internal
> > attenuator that is switched in below 1.8MHz. On ICOM radios, the
broadband
> > transformers also run out of performance below 500kHz. This general
> problem  seems to
> > be more severe with radios that have already had their  performances
> streatched
> > to cover the 6m band.  e.g. The FT1000 and TS850  work well ( 28MHz max)
> but
> > the IC756 746 and the FT817 are about 20dB  'deaf'.
> >
> > Adding a yxm/mrf pre-amp will overcome the loss of the input attenuator
> (apx
> > 10dB) and will have a few extra dB to help things along. However, I have
> had
> > a couple of mails from people who expected the pre-amps to work when
they
> > were added to simple small verticals or wires.
> >
> > The pre-amps are 50 Ohms (ish) in and out while the  impedance of a
> typical
> > 7MHz vertical is a very small fraction of 1 Ohm. The loss between them
is
> > huge. You need a matching network.
> >
>
> I built a pre-amp/LFtuner to add to the front end of a IC-706, which I
used
> when on vacation in Marrakech, October 2003. The unit used two G0MRF
preamps
> in series and must have worked reasonable well because it was used in a
> crossband 136kHz/7MHz QSO with G3AQC. The antenna was a 20m long doublet,
> fed with 6m of 400ohm ladder line, resonated using the tuner against the
AC
> supply ground.
> The pre-amp/LF tuner was described in RadCom, Antennas column, December
> 2003.
> I have a PDF file of the article for anyone who would like a copy.
>
> Peter, G3LDO
>
>
>