From: "Mike Dennison" <mike.dennison@rsgb.org.uk>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 22 Mar 2000 13:43:54 -0000
MIME-Version: 1.0
Content-Type: text/plain; charset=US-ASCII; format=flowed
Content-Transfer-Encoding: 8bit
Subject: LF: Two band operating
Message-ID: <E12XlW4-00033J-00@mserv1c.u-net.net>
Precedence: bulk
Reply-To: rsgb_lf_group@blacksheep.org
Sender: <majordom@post.thorcom.com>

For what it's worth, I now operate very easily with the station 
optimised for both 73kHz and 136kHz with a fairly fast manual 
changeover.

The connection from the antenna to the coil can be made either to 
the 136kHz tap or the 73kHz tap (actually not a tap but the top of 
two coils). This works fine for transmit on 73 and receive on 137. To 
transmit on 137 I simply change the tap on my matching 
transformer as the impedance on slighly different.

My changeover time is about 30 seconds - more than adequate for 
two-way QRSs.

I find it important to optimise the antenna tuning on receive 
because the Datong LF converter has a broadband front end and it 
needs as much input selectivity as it can get.

Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm