Message-ID: <002401c0886e$6949d3c0$9c1686d4@ericadodd>
From: "g3ldo" <g3ldo@ukonline.co.uk>
To: rsgb_lf_group@blacksheep.org
References: <008701c0864a$3cc020a0$0301a8c0@steve> <006701c087c8$f786f600$995c01d5@z0w6t5>
Subject: LF: Re: Bandwidth and receivers
Date: Sat, 27 Jan 2001 13:09:01 -0000
MIME-Version: 1.0
Content-Type: text/plain; charset=iso-8859-1; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

 Bill, G0AKY said

> All agreed in principal but there is one nail you forgot the LF band hr is
> only just over 2Khz wide

I get the impression from Bill's comment that he, and others, think QRSS is
a wide band mode.
All other things being equal the bandwidth is inversely proportional to the
data rate, which means the bandwith for a QRSS signal is much less than a
standard CW signal. You can check this out for yourself by just looking at
these signals with QRSS SW.
When we do the transatlantic tests we often have a group of signals
transmitting a few Hz apart and each one is perfectly readable (see Ko
Versteeg's .JPG on page 98 of the LF Experimenter's book).
The main limitation of having two CW signals closer than, say, 100Hz apart
is the receiver filter. You can have very narrow filters. I have a level
meter with a 20Hz filter that certainly selects one signal from the other
and you can read CW with it provided it isn't sent too quickly. Its main
problem is that it converts every bit of noise and QRM to a tone the same as
the signal you are receiving and this is very 'wearing' after a short while.

Most problems with receivers are due to front end non-linearity. The worst
receiver I have used that has this problem is the Daytong converter.
Nevertheless, this converter can provide excellent 'ears' (as G3XDV can
attest) provided steps are taken to reduce the input with an attenuator
and/or preselector if you are using a large antenna.

The problem often arises when you change from a small antenna to a big
antenna. You often see it with a special event station using a big antenna
put out a huge signal but have problems hearing anyone. Seasoned LF
DXpeditioners, such as the 'Two Daves and a Graham' take with them their pet
receiver front end signal level box.
When I operate from GB2CPM the Loran comes pounding in at S9. I have to
insert some 18dB of front end attenuation plus the AIP before the weak
signals become readable.

I live only a few miles from Laurie, G3AQC. His signal with me is S9 +35dB.
(I guess I must be as strong with him). I am able to operate on the band the
same time he is on provided I use the attenuators and provided I don't get
too close in frequency!


Regards,
Peter, G3LDO

<g3ldo@ukonline.co.uk>