[CQ-Contest] Voice Keyer

[Dave Pruett]

John,

I've been using the older style MFJ  voicekeyer (the model 432) with my 
laptop since 1997.  I've rigged up the parallel port interface to trigger 
the messages from the logging program F1-F4 keys.  I had to mess with it a 
little to get hum out of the mic, but then it worked FB from WP3X in '97 & 
'98, plus numerous Field Days and such since then.

The hum problem has to do with the fact that in the MFJ-432, the mic ground 
is not isolated from the chassis.  MFJ was too cheap to put in a 600:600 
isolation transformer (like W9XT did), so they tried to isolate the mic 
ground with some 1000 uH chokes between the electronics and chassis ground, 
the logic for which escapes me.  When used with the TS-930 I had then, this 
hummed badly but after shorting out the chokes it worked perfectly, also 
with the TS-850 I traded up to.

Its been my experience that ICOMs are the worst in terms of humming from 
unisolated mic grounds.  For these, I got a small mini-box with input and 
output connectors and wired a Radio Shack 600:600 isolation transformer to 
these connectors.  Oh yeah, you need a small capacitor (a 1uF/15V 
electrolytic will do) between the transformer and the output connector to 
isolate the +8V that is superimposed on the ICOM mic lead.  This combo 
(MFJ-432 and isolation box) has worked perfectly on five or six different 
ICOM models on which it was tried.

Since you mention the DVS-2, obviously you're using a Yaesu radio.  I can't 
recall using the MFJ-432 with the FT-1000Ds which are the prevalent radio 
at K8CC.  We have six W9XT cards here in the regular station setup and they 
work perfectly with the 1000Ds.

The 432 is no longer available, but the newer MFJ-434 uses the same IC 
technology, which is also the same that is used in the W9XT card.  I don't 
know if the circuit is the same, or if you'd have to fool around to solve 
the ground isolation/hum problem.

73,

Dave/K8CC


At 06:23 PM 1/4/02 -0600, kk9a at arrl.net wrote:

>I'm looking for recommendations on voice keyers.  I've been using a Yaesu
>DVS-2 for four years and I've never liked the audio quality.  I've
>considered the W9XT card, which may be good for home use but it won't work
>for contest expeditions using a laptop.  So tell me what you're using and
>how you like it!
>
>73,
>John
>
>
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