Date: Sat, 18 Sep 2004 10:44:27 +0200
From: Dick Rollema <dickrollema@casema.nl>
To: LF-Group <rsgb_lf_group@blacksheep.org>
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Subject: LF: SL6440/mixer
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To All from PA0SE

When I had to decide what type of mixers to use in my new TRX, a doubly 
balanced passive diode mixer or the SL6440, I chose the latter for the 
following reasons.

1. The SL6440 amplifies so there is no need for an amplifier between the 
mixed and the following IF filter.

2. The SL6440 requires very little LO power

3. There is no need for critical terminations of the ports, as is the case 
with a passive mixer.

Both PA0KDF and I found that the LO signal appears  very strong in phase at 
the output pins 3 and 14 of the SL6440 and  this signal must be suppressed 
to enjoy the full large signal capability. I did this by connecting 
a  parallel tuned circuit between the pins with the centre of the coil 
grounded for RF and connected to 12V. The circuit is tuned to the IF and 
the IF signal extracted by a link over the coil.

I also use a balanced circuit at the input of the mixer.

The large signal behaviour of the receiver is very good.  Using a 2 x 20 m 
dipole on 7MHz there is no trace of IM  when listening on a winter 
night.  Not even when the 12dB preamplifier is switched on. As a test of 
course, the amp is not needed below 24MHz. But in this respect the Cohn 
bandpass filter (bandwidth 180kHz) at the input of the receiver helps  as well.

The SL6440 is no longer in production, though they can still be found. But 
if you are going to use one better buy some spares as 
well.  Fortunately  they are not very expensive.

73, Dick, PA0SE