[Fourlanders] Contest Computer RFI

Tue Oct 11 08:33:29 EDT 2005

Brian:
Good list of points and facts for reference.

Before running any RF with your test bed, it might be worth testing all
of the same contest Writelog equipment in a static condition for a week
to help ensure we really have an RF problem (maybe something's shaky
with a network component ?) and to ensure that all the PCs stay on line,
server keeps pinging all the clients, things like that. If that seems
stable, then start adding RF emitters.

Also, I wonder how much current the hubs draw ?? Might be worth thinking
about running them from batteries. That's one good way of reducing RF on
the voltage lines. I've got some 24Ah telephone company 12 volt
batteries if we need them for this.

Also, some of your 6 points made about RF proof trailer interconnecting
cable is exactly what I was thinking. In addition, I hope to find enough
of the clamp on ferrite "mufflers" to install right at the hubs on the
peripheral PC cables coming into the hubs.

Your thought about RS-232 comm between everything is also a good
suggestion, except we may have a shortage of comm ports on the laptops
or PCs since the WriteLog serial data from the radios occupy one comm
port on the PC already.

I had also thought about what it possibly would take to run slower "Thin
Net" Ethernet with RG-58 coax. I know there are lots of thin net AT
style cards available (with the BNC connectors) to be had from the
surplus houses.

Ron 
WW8RR

-----Original Message-----
From: fourlanders-bounces at contesting.com
[mailto:fourlanders-bounces at contesting.com] On Behalf Of Brian McCarthy
Sent: Monday, October 10, 2005 9:32 PM
To: fourlanders at contesting.com
Subject: Re: [Fourlanders] Contest Computer RFI

Some facts:
1. The link from "great white" to the smaller trailer was run at 10MHz.
2. Two different hubs were tried in the smaller trailer. The second hub
tried was of all metal construction.
3. The amplifiers for both 50 and 222 MHz where tied to trailer frame
ground by short braided line (about 18 inches.) 4. The measured
resistance from neutral/ground to trailer frame + skin in the great
white measured < or = 1 ohm.
5. While it seemed there was a possible correllation between 2m antenna
trouble and network problems, the network was problematic through to the
end of the contest.
6. Windows firewall was turned off on all the PC's for the contest.
7. We were using static IP addresses and had set network DDE and other
settings as recommended by the Writelog documentation.

I know there are more significant details that could be used to fill in
an "is vs. is not" chart. What did I miss?

I have three of the five PC's that were connected to the contest network
here in my basement. In the next couple of weeks I will start a test bed
where I will run 3-5 PC's with Writelog in a manner like what we do on
the mountain. I will connect my K2 and may ask to borrow one or two
other radios that can be RS-232 connected. I would like to run the main
part of the test for days, weeks or even a couple of months. That will
be easy with my hardware, but borrowed radios may be the challenge.

I have been playing with thoughts of how to RF-proof 10/100-Base-T
cabling. I liked the theoretical advantage of the piece of CAT-6 that we
used between the trailers. In all of the documentation I have been able
to find, it looks like Ron is correct in observinng that only 2-pair are
required for 10-Base-T and maybe also 100-Base-T.

Here is a thought that I had for a, hopefully, RF-proof cable and
termination:
1. A piece of shielded CAT-6.
2. Shield connected to a ground rod outside the trailers.
3. If only 2-pair are required and 4-pair are in the cable, ground one
pair to one end only at each end.
4. Put toroids (type 43?) on the data carrying leads right before they
terminate to the hub in each trailer.
5. Use metal case hubs, or install the hubs into metal boxes bonded to
trailer frame/skin with minimum lead lengths.
6. Discard the wall warts by running the hubs from the 12VDC used in the
adjacent station (may require internal mod's to hub).

Bob, K4SZ, have you ever looked at whether you are able to measure any
signnificant interference between 2304 MHZ and WiFi hardware? What kinds
of testing would we need to do before we would trust WiFi as a
connection between the two trailers? And just in case anyone is curious,
the WiFi access point that I was able to "connect" to (really associate
with) was 11.1 miles away and was an optical path. I believe I had a
rather solid 1Mbps link, but no IP address so no internet or otherwise
was possible.

I don't think that RF into the ethernet cables is our only problem.

Some other thoughts that were discussed on the mountain include trying
to quantify the amount of data bandwidth occupied by 4+ stations with
RS-232 connected radios. We should run the network with a DHCP server
instead of static IP. There were some other ideas, but those escape me
at the moment.

We never want to be on the mountain without some way of connecting to
the DX Clusters. Neal made a number of decisions about where to point
the 6m antennas at significant moments in the contest due to the
information available on the cluster. I spotted hearing one of the
larger northeast stations on 222 MHz and ended up working that station
and quite a few others. I believe that spot helped alert the northeast
that we were hearing them and that we should be able to work them. Next
week I expect to take delivery on a new datacard like the one we used
during this past contest. While I am not getting it just for contesting,
it helped in the emotional part of the justification to be able to use
the card for contesting.

I need to get back to a few other things, but I hope this was useful to
all. I like the discussion and I am willing to listen to ideas and
investigate what it will take to have rock solid networking and internet
connectivity for the contests.

Cheers,
Brian
NX9O

Rogers, Ron wrote:

>Another thing to think about in reducing the amount of localized RF in 
>or around the equipment is the fact that we DON'T GROUND ANYTHING and 
>everything is just "floating".
>
>Yes, it is difficult to find a decent way to ground the trailers, the 
>Ethernet hubs being used, etc. But it is worth brainstorming to see 
>what we could do. The high speed, high impedance differential 
>line-driver, line-receiver amplifier circuits used in those hubs are 
>simply packaged in their plastic cabinets with no shielding (I 
>suspect). In any case, I know there is no frame grounding and simply
have 2 wire "wall warts"
>powering them which means not even a having frame ground brought out to

>an "Earth Ground" pin.
>
>We old-time repeater builders designing equipment for mountaintops with

>lots of 500 watt pagers and 2-way systems have learned by our share of 
>"hard knocks" how important some of these small details are.
>
>Also, the suggestion of switching Ethernet gears down to 10 Mbs may 
>have merit and should be tried.
>
>I'll also be shopping around for some more of the clamp-on ferrite 
>cable "decouplers" we use on some of our NCR equipment. I've had to 
>install some of the same type on my RS-232 4800 baud cables at the 
>Sawnee Mountain repeaters site to maintain reliable low speed RS-232 
>comm between the multiple repeater controllers and the "modem gateway"
>computer. We run Win Laplink on that computer to provide remote console

>programming capability of the repeaters at the QTHs of the repeater
>technical support people.     
>
>Ron
>WW8RR
>
>
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>

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