On Wed, 20 Feb 2008 23:35:04 -0600, Ed Gray W0SD wrote:
>I got my $100.00 worth of type #43 ferrite that are exacty the ferrite
>that has been recommended for curing router birdes on this reflector. I
>have wrapped 9 turns of the CAT cable through and around the ferrite
>core and it makes absolutely no difference.
Several comments.
1) #43 is NOT a good choice for suppressing RFI below 40 Meters. It is VERY
effective at 40M and above. For RFI on 80M, 160M, and the AM broadcsat band,
you need #31. If your problem is ONLY on AM broadcast and 160, #77 and #78
will work.
>Today three of us hams worked on the birdie problem for quite awhile.
>Here is what we found. It seems to be something to do with the birdies
>being generated in the computer, ie the circuitry that talks to the
>router.
2) The only ETHERNET BIRDIES I have ever heard below 30M was a VERY weak one
on 80 when I lived in Chicago. Common ETHERNET birdies on the CW bands are at
14030, 21052, 28015, and the bottom of 6M. Frequencies vary, because these
clocks are not well controlled -- if you're in a populated community, you'll
hear your own birdies, then a few hundred Hz away you'll hear your neighbors.
3) Both ends of an Ethernet cable are transmitters of RFI trash.
4) Virtually ALL computer stuff and digital stuff can generate trash. The HF
stuff mostly comes out on the interconnecting wires -- monitor cable, modem
cable, Ethernet cable, power supply cables, mouse cable, keyboard cable, audio
cables, etc., because those are the best antennas for HF frequencies.
5) ANY digital stuff, anything with a power supply, can radiate trash directly
from its own internal wiring if it is not well shielded. When you've killed
the radiation from your Ethernet cables with chokes, you may still hear direct
radiation from that internal wiring.
>It happens with all my computers but on my newest one when you
>shut it off some circuitry stays powered up and the light on the network
>card stays on and the birdies only go away when you pull the AC cord off
>the computer.
Are we talking topband, or higher HF bands? See #2 above.
>I also have an AC line filter on the computer which cured my switching
>power supply noise. We also tired the ferrite core on the power cord to
>the Router which was a desperation idea as our tests seem to indicate it
>is being generated in the computer if the router signal is coming into
>the computer. We hooked the DSL modem right to the computer and the
>birdies are gone. It would seem the birdies are being radiated by the
>CAT Cable and the ferrite is not attenuating it at all.
I suspect multiple sources or coupling mechanisms. The chokes you describe
should be effective for what the CABLES are radiating at HF, but not on 160M,
and not great on 80M. But I've never heard ETHERNET create birdies below 30M,
so that stuff is coming from something else! Maybe the monitor, maybe the
computer, maybe one of the power supplies. And the chokes will have NO effect
on what's radiated directly by the internal circuitry, or from cables they're
not on.
I also tried a
>clip on ferrite and no effect. I don't have any shielded Network cable
>and all I read is that really should not be necessary.
Right.
>I also have a laptop with a wireless card and it gives no problem(no
>birdies)as long as you don't have a CAT cable hooked to one of my three
>computers and as I said there is not problem if the computer is not on.
I suspect that particular router is a major element of the problem, with
shielding and power supply being likely suspects. To eliminate the power
supply,try running it on a battery (or if the router runs on 12V, the power
supply from your ham gear).
>The only solution so far that would seem to work is to buy a wireless
>card or the USB wireless adaptor for each desktop computer and forget
>the CAT cable. I base this on having no problem with using the wireless
>card in the laptop.
That's a good idea. If wireless networking works for you, by all means use it.
I'm using it for nearly all my networking at my QTH in CA. I'm streaming audio
from a jazz station 24/7, doing email, reading the cluster, communicating from
one computer to another (my office, my XYL's office, my shack) with no
problems I can blame on RF. Now, I DO have problems I can blame on how one
machine or another negotiates the wireless networking protocols, but once I
have each computer logged on, all is well.
>Every computer hooked to the router has its own set of birdies so with
>three computers hooked up I have quite a number of birdies, some very
>loud depending on the antenna orientation. If I just have two on there
>are less and with just one on there are not all that many. I can rank
>the computers as to which produces the most birdies and the least.
How long are these cables? If they're more than about 1/10 wavelength at the
frequency of the birdies, each end of each Ethernet cable needs a choke. And
that choke needs to be "tuned" to the ham bands where you're hearing those
birdies. One of the advantages of the #31 material is that it is more
"broadband" by a factor of 2:1 than #43 -- in other words, you are more likely
to cover three harmonically related ham bands with #31.
I STRONGLY recommend good vintage laptops for ham logging. My T22 and T41
Thinkpads have been rock solid for all forms of business use and ham
logging/control for five years. If you want a bigger screen or keyboard, buy
one and plug it in. A T41 has been my primary biz computer for four years, the
T22 for three years before that, and when I bought the T41 it became my shack
computer. They are not completely free of RFI issues -- I still hear some
trash from the video system under some conditions -- but nothing serious.
BTW -- a better place to be asking these questions is the RFI reflector. There
are some very sharp RFI guys there, and HF RFI is sort of off topic here. And
check out my tutorial if you haven't already.
http://audiosystemsgroup.com/RFI-Ham.pdf
73,
Jim Brown K9YC
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