Kio2 cablength

[kf4yox]

 Hi I was wondering if there would be a problem using a 25 foot length of
cable from my K2 to the computer.
   73 and Thanx Sam KF4YOX

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[Don Wilhelm-3]

Sam,

Since the computer to K2 cable carries only RS-232 signals, I should think
25 feet should pose no problem - why not just try it and report the results.
It certainly will not break anything if you construct the cable as shown in
the KIO2 or KPA100 manuals.

However, do not use a standard computer serial cable - IT WILL CAUSE BAD
THINGS TO HAPPEN TO YOUR K2 - the cable should have only TXD, RXD, and
signal ground lines connected (and the shield at the K2 end), plus the
handshaking jumper at the computer end.

73,
Don W3FPR

> -----Original Message-----
>
>  Hi I was wondering if there would be a problem using a 25 foot length of
> cable from my K2 to the computer.
>    73 and Thanx Sam KF4YOX
>
>
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[Matt Osborn]

Since the HIO2 communicates at 4800 baud, 25 feet should work well.

for more info see:

http://www.connectworld.net/cable-length.html



On Mon, 4 Jul 2005 21:18:34 -0400, <[hidden email]> wrote:
>
> Hi I was wondering if there would be a problem using a 25 foot length of
>cable from my K2 to the computer.
>   73 and Thanx Sam KF4YOX

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[Jim Brown-10]

On Mon, 4 Jul 2005 21:18:34 -0400, [hidden email] wrote:

>Hi I was wondering if there would be a problem using a 25 foot length of
>cable from my K2 to the computer.

If you're going to run a longer cable, I STRONGLY recommend using twisted
pair for the connection between the computer and the K2. The best solution
is shielded CAT5; the second best solution is unshielded CAT5, or two runs
of braid-shielded twisted pair. This will do two things. First, the
twisted pairs will reduce the susceptibility of both the K2 and the
computer to "RF in the shack" problems. Second, CAT5 cable has very low
capacitance, which allows RS232 to work for longer distances.

To gain the benefits of the twisting, use one pair (orange and
orange/white, for example) to connect pin 2, with orange to pin 2 and
orange/white to pin 5. Likewise, green to pin 3, green/white to pin 5. The
overall shield should go to the DB9 shell on each end, not to pin 5.

If you are using UN-shielded twisted pair, connect the return of each pair
to the DB9 shell, NOT to pin 5. This puts a "band-aid" on pin 1 problems
on each end.

These techniques solved a nasty RFI problem for me that was causing my
computer to grind to a halt at about 10 watts out to a long wire antenna
that ended in the shack and ran right past the RS232 cable. Now I can run
the K2/100 with my Titan amp at full power with no RFI problems.

For more about pin 1 problems, see my website.  

http://audiosystemsgroup.com/publish

73,

Jim Brown K9YC


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[Jack Brindle]

Jim;

I've learned quite a bit from you, and have a question about what you  
are saying here.

On Jul 7, 2005, at 8:48 AM, Jim Brown wrote:

>
> To gain the benefits of the twisting, use one pair (orange and
> orange/white, for example) to connect pin 2, with orange to pin 2 and
> orange/white to pin 5. Likewise, green to pin 3, green/white to pin  
> 5. The
> overall shield should go to the DB9 shell on each end, not to pin 5.
>
> If you are using UN-shielded twisted pair, connect the return of  
> each pair
> to the DB9 shell, NOT to pin 5. This puts a "band-aid" on pin 1  
> problems
> on each end.

We have gone out of our way in the RS-232 cables to avoid ground  
loops by not connecting the DE9 shell at one end (or in the case of  
the KIO2 cable, both). I have also seen this technique described  
(reference Bob Heil's web page), indicating that it is best to leave  
the computer end of the shield unconnected. So my question is why the  
suggestion to connect both ends here? Why doesn't this create the  
very ground loop problem we are trying to avoid?

Thanks. My engineering career has taught me that grounding, like RF,  
is magical - I continue to learn things about it that change my way  
of thinking.

- Jack Brindle, W6FB
------------------------------------------------------------------------
---------------------


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[Don Wilhelm-3]

Jack, Jim and all,

Adding to that grounding 'magical stuff', what I learned in large system
computer design and testing experience was that shields are only DC grounded
at one end, and that end is the 'driving' device or in the RS-232 world,
that would be the box defined as the DCE - in the DTE devices, the shield
would be grounded through a  capacitor, or alternately left open.  This was
accomplished in the device wiring itself, the cable shield was always
connected to pin 1 at both ends.

Differences in the potential of the chassis (yes - well grounded to the
power ground bus) of a box on one side of a raised floor computer room as
compared with a box on the other side could be substantial enough to cause
current to flow through the shields if both boxes would have had the shield
directly bonded to the chassis.  DTE units that did not follow the shield
grounding rules were not capable of using long communications lines.  But
that was large computer systems with terminal controllers and a bunch of
distributed terminals, the world today with PCs and LAN and WAN connections
is quite different.

Anyway, in my mind, Jim's recommendation to connect chassis ground (pin 1)
on both ends could cause a ground loop noise problem if the computer and K2
chassis are not at the same potential.  Can you elaborate a bit more for us
here Jim?

73,
Don W3FPR

> -----Original Message-----
>
> Jim;
>
> I've learned quite a bit from you, and have a question about what you
> are saying here.
>
> On Jul 7, 2005, at 8:48 AM, Jim Brown wrote:
> >
> > To gain the benefits of the twisting, use one pair (orange and
> > orange/white, for example) to connect pin 2, with orange to pin 2 and
> > orange/white to pin 5. Likewise, green to pin 3, green/white to pin
> > 5. The
> > overall shield should go to the DB9 shell on each end, not to pin 5.
> >
> > If you are using UN-shielded twisted pair, connect the return of
> > each pair
> > to the DB9 shell, NOT to pin 5. This puts a "band-aid" on pin 1
> > problems
> > on each end.
>
> We have gone out of our way in the RS-232 cables to avoid ground
> loops by not connecting the DE9 shell at one end (or in the case of
> the KIO2 cable, both). I have also seen this technique described
> (reference Bob Heil's web page), indicating that it is best to leave
> the computer end of the shield unconnected. So my question is why the
> suggestion to connect both ends here? Why doesn't this create the
> very ground loop problem we are trying to avoid?
>
> Thanks. My engineering career has taught me that grounding, like RF,
> is magical - I continue to learn things about it that change my way
> of thinking.
>
> - Jack Brindle, W6FB
> ------------------------------------------------------------------------
> ---------------------
>
>
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[Margaret Leber]

W3FPR - Don Wilhelm wrote:

> ...what I learned in large system computer design and testing
> experience was that shields are only DC grounded at one end, and that
> end is the 'driving' device or in the RS-232 world, that would be the
> box defined as the DCE - in the DTE devices, the shield would be
> grounded through a  capacitor, or alternately left open...
> Differences in the potential of the chassis...of a box on one side of
> a raised floor computer room as compared with a box on the other side
> could be substantial enough to cause current to flow

When I was working for a very large IBM mainframe shop in the mid-1970s,
we had the Mother Of All Serial Devices: an IBM 3705 communications
controller. This beast was rolled into our raised-floor machine room and
left standing on its shipping wheels next to the Comten controller it
was intended to replace.

The controller, a computer in it's own right, woul not run for more than
a day or so without halting due to a hardware-detected fault...denoted
by the illumination of one or more of the dreaded "red light"
indications on it's Star Trek TOS-like front panel (and the immediate
sessation of any data flow though it from the modem bank to the
processor complex it was attached to).

After field-replacing every circuit board in the box (and it was a very
big box) and scheduling the replacement of the 370 Motherboard Itself
(which was more of a "passive backplane" than what we call a
"motherboard" in a PC today), IBM Field Engineering began to notice that
every time they went to place a scope probe on signal lines in the box,
it would crash. This was odd enough, until the time their tech reached
out to place the scope probe on a line, and the box crashed just
*before* he touched it.

Subsequent investigation disclosed that the weight of the 3705 had
caused the alignment of the panels of the raised floor to shift slighly,
  creating two huge insulated sections of floor in a room that was
easily 1,000 sq ft. Standing on one of the floor panels on the boarder
of the two sections could cause the panel to rock slightly in place like
a table with uneven legs (which is effectively what it was), closing a
circuit between two huge capacitor plates (which is effectively what
*it* was), and causing a surge of static to race into the surprisingly
delicate device. Of course one of the "landmine" floorplates was right
in front of the light-bedecked console...

  73 de Maggie K3XS

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----/(, /|  /| http://voicenet.com/~maggie SCWCD/ is to preserve order/
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/________________(_/_(_/_______AMSAT 32844_/<[hidden email]>/


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[Jim Brown-10]

Hi guys, and thanks for the good questions.

Add me to the list of those who strongly believe in connecting the shields of
BALANCED interconnecting cables at the sending end only at low frequencies, and
through a capacitor at the receiving end if the cable is a significant fraction of
a wavelength at the frequency of an interfering signal. But it's important to
understand WHY we need to do that -- the pin 1 problem!  

The key word here is BALANCED. Serial connections are UN-balanced, so any voltage
drop on the return is added to the signal. So one thing we've learned in the audio
world is to use as much beef as we can in the return of unbalanced circuits. If
you reduce the resistance of the shield by half, you reduce the hum/buzz by 6 dB.
Reduce the resistance by a factor of 5 and you reduce hum/buzz by 14 dB. Bill
Whitlock and I both recommend using video coax (8241, 8281) that has a beefy
copper braid for unbalanced audio connections, and this is one reason why.

Another point, that I think we talked about in Dayton, Don, and that I've talked
about on the reflector, is that the pin 1 problem is a major reason that we NEED
to prevent that shield current. If you can eliminate the pin 1 problem, you've
eliminated much of the coupling of that shield current into the equipment. The IR
(or IX) drop is still there, but reducing the shield resistance helps that.

Reminder of what the pin 1 problem is: A cable shield SHOULD go to the shielding
enclosure of the equipment at each end. In the old days, that was easy -- the
connector shell was bonded to the chassis by virtue of its mounting hardware.
Today, in the interest of making things easier and cheaper to build, connectors
are terminated to the circuit board, and a circuit trace connects the shell to the
chassis eventually. But that circuit trace has both R and L, and other circuitry
is also connected to that trace. So any shield current (like RF current induced on
that cable shield, and any power-related hum/buzz that results from voltage
differences between the connected equipment) flows on that trace and there's a
drop across the trace. That drop gets injected into the circuitry based on the
whim of the circuit layout specialist, and we've got RF in the shack (and buzz in
the audio).

Now, if you were using SHIELDED CAT5 (which is hard to find and I do have some), a
case could be made for connecting the shield at only one end, and using the pairs
as I've described, and with their returns tied to pin 5. But that shield doesn't
do much below about 20 MHz -- I've tested it with the K2/100 feeding that long
wire at full power all the way up to 10 meters, and it only improves stability
slightly on 15m and more on 10m. And that's with the wire running within a foot or
so of the RS232 cable!  I haven't done any testing of the long wire interface at
high power (KW amp) above 80 meters, because the wire doesn't work well enough as
an antenna above 80m for me to want to use it. :)  

All of the RS232 cables I've built for my rigs have the cable shields tied ONLY to
the DB9 shell on both ends. So far, I've built interfaces for a TS850 (also works
on the 791A VHF/UHF radio), Omni V, Icom 746 (which I use on 6m and 2m), and my
K2's. On the radio end of the 850, the shield goes only to the shell of the DIN.

BTW -- the second reason why you want a beefy shield on coax that encounters noise
below 1 MHz or so is that the shield cutoff frequency is reduced in direct
proportion to that resistance! The shield cutoff frequency is the low frequency
limit of where the shield starts working to cancel magnetic coupling to the center
conductor -- below that frequency, it provides only electric field shielding. For
a really beefy double copper braid, the cutoff frequency is on the order 1 kHz.
For a typical foil/drain shield, it's more like 50 kHz. Also, shielding
effectiveness above the cutoff frequency is inversely proportional to that
resistance, so dividing the shield resistance by 10 improves the magnetic field
shielding at 200 kHz by 20 dB. There's a nice derivation of this in Henry Ott's
book.

Another point re: connecting or not connecting at both ends. For the coax shield
to work to cancel magnetic coupling, it must be connected at each end at the
frequency of the interference. If the interference is at 200 kHz, you would need a
capacitor that looks like a very low impedance at 200 kHz. No problem, you just
need to choose the right value of you have that kind of interference.

73,

Jim Brown K9YC

On Thu, 7 Jul 2005 14:49:55 -0400, W3FPR - Don Wilhelm wrote:

>Adding to that grounding 'magical stuff', what I learned in large system
>computer design and testing experience was that shields are only DC grounded
>at one end, and that end is the 'driving' device or in the RS-232 world,
>that would be the box defined as the DCE - in the DTE devices, the shield
>would be grounded through a  capacitor, or alternately left open.  This was
>accomplished in the device wiring itself, the cable shield was always
>connected to pin 1 at both ends.




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