[time-nuts] Z3805 utility, Was: AW: (no subject)

Didier Juges didier at cox.net
Sat May 22 22:21:17 UTC 2010

Bill, I think you got it backwards. +/- 12V is typical for RS-232, 0/+5V is
for RS-422 and RS-485.

No RS-232 receiver should be damaged with +/- 12V or even +/- 15V because
that is their normal operating voltage.

Also, RS-422 and RS-485 have something like 25V common mode tolerance (not
sure what the actual spec is there,) so that the RS-422 and RS-485 receivers
should not be damaged by 15V either. The RS-422 drivers are pretty low
impedance, while the RS-232 drivers are current limited, so I don't think
that connecting an RS-232 driver into an RS-422 driver will damage either.

However, most recent (<10 years?) RS-232 receivers will work with a 0/+3V or
0/+5V input, conveniently having a threshold a few 10's or 100's of mV above
ground, even though the original RS-232 spec required receivers that work
with as low as +/- 3V, and drivers that deliver +/- 9V minimum. Many
commercial systems use +/- 5V drivers for RS-232 (B&B Electronics sells a
lot of converters with these voltages). This is a deliciously sloppy spec
that nobody has met in the last 25 years probably, yet works most of the

The one thing to avoid is to short an RS-422 (or RS-485) driver to ground,
as that can actually cause damage, maybe not every time, but definitely not
recommended. These have relatively high current output capability to drive
long lines.

Didier KO4BB

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bill Hawkins
Sent: Saturday, May 22, 2010 3:09 PM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

When all else fails, get out the voltmeter.

Do you have power to the antenna? Is it the right voltage? All the way to
the antenna?

What volts are on pins 2 or 3 relative to pin 7 in the comm connector?

If you see 12 volts, that's RS-422. You may have burned out your computer's
serial port.

If you see less than 5 volts, that's RS-232 and all should be well, unless
you see zero volts.

I may have the RS-xxx volts somewhat off because my memory isn't what it
used to be.

The guy you bought it from should be able to help with comm basics.

Bill Hawkins

-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Robert Benward
Sent: Saturday, May 22, 2010 2:08 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Z3805 utility, Was: AW: (no subject)

Hi All,
I hooked everything up and I still get nothing.  I can't seem to establish
communications  with the Z3805.  I tried a 
null modem as well, in case the cable (supplied) was wired with the wrong
connector gender.  I see a green blinking 
light inside, it he left rear corner of the box.  Everything is warm, but
nothing else.  Any ideas?


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