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" <[email protected]>
To: <[email protected]>
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
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