On 12/30/2010 4:52 PM, Dale Svetanoff wrote:
> Jim, Roger, and All:
> Jim and Roger have made excellent points in their respectuve postings. I
> would just like to add my comments regarding overall RFI issues with
> commercial equipment:
> I have spent the past 11 years working in military and aerospace EMI/EMC
> design and test. In my case, most of the emphasis was on equipment design
> with the goal of passing the required EMC tests on the furst try. That is
> because mil spec testing (and even commercial aerospace testing to RTCA
> DO-160 specs) is very expensive. You must keep in mind that even the best
> designs WILL have radiated emissions. The issue is: at what level and in
> which frequency ranges? Because so much equipment is frequently jammed
> together in aircraft cockpits or the radio ops areas of military vehicles
> or base stations, the equipment must not interfere either with itself or
> with other co-located equipment. (If interference occurs between radio
> systems because of antenna-to-antenna coupling, then costly co-location
> filter networks may be required. These are similar in concept to the
> cavities used for repeater systems.)
> Commercial gear for normal industrial and/or consumer use has no such
> requirements imposed upon it. From roughly 26 MHz on up, the radiated
> emissions allowed by FCC Part 15, Class B equipmant will be on the order of
> 20 to 30 dB greater than allowed for military or commercial aerospace
Experience would indicate it goes a lot lower in frequency than that.
> That's a LOT of extra signal. As has been stated on this
> reflector many times in the past, most radiated emissions come from
> connecting cables - be they power cords, Ethernet, discrete signal&
> control, audio, or whatever. Good equipment design will minimize those
> emissions, but so will proper cable design and installation. The postings
> already made go into enough detail involving chokes, by-passing, shielding,
> and so forth.
Oh, so may years ago I had set up with stations on each band. A good
portion of the station was in a home made console.
http://www.rogerhalstead.com/ham_files/boat1.htm Not all the same
equipment in this photo but it's the same console. I could basically
use any HF antenna on any HF rig and had several VHF and UHF stations as
Behind the console was the usual mass/mess of Coax, power, and control
cables. I decided it needed a bit of neatening up. So after two days the
cables were neatly harnessed and bundled keeping the three types of
cable separate. I was really proud of the way it looked. They I started
firing up rigs. I think every thing interfered with every thing else.
Nothing seemed to work right. It took me over a month to get all of
that back working like it had been
> My point is that equipment design and cable treatment can only go so far in
> reducing emissions that, in many instances, are basic to the product. (A
> high speed Ethernet cable WILL radiate harmonic energy - it's part of the
> game. The issue is to reduce the radiation as much as possible.) One BIG
> part of the EMC control triad that is overlooked all too often is: what is
> the separation distance between the offending source (which can be both a
> piece of equipment AND all of the cabling associated with it) and the
> victim? In most cases, we regard the victim as being our radio receiver.
> Now, think about it- is the victim the receiver or the antenna to which the
> receiver is connected? I think you will find that in all too many
> instances, the real problem is that the antenna (or parts of it) are too
> close to the offending source.
I long ago gave up trying to be careful with routing. Now I throw it
together and check to see if it works, IF it doesn't then I'll make a
change. So far this approach has worked well.
There is one exception, or at least partial exception.
> Here's some food for thought: Mil spec EMC testing is done with a
> measurement distance of 1 meter from the unit under test; FCC tests are
> done at 3 meters from the unit under test, and the allowed limits are
> higher, as well (for equivalent frequency ranges). That difference alone
> is good reason to make certain that you do not locate equipment that is
> potentially an RFI source too close to your antennas. Note that the
> antennas might very well be outdoors and the equipment indoors, but unless
> your house is built like a Faraday cage,
It is<:-)) My shop is the exception I was talking about. The entire
interior is bonded "Barn Metal". It's not a good place to try your cell
phone or HT. The cell tower is less than two miles line of sight and I
can see it out the South Shop window, which is where you need to be
standing for even reasonable reception. 5 Watts on the HT to the 147.00
repeater at slightly less than 6 miles is a lost cause. Also all coax
and control cables run in grounded, surface mount EMT.
http://www.rogerhalstead.com/ham_files/boat6.htm Outdoors they run in
PVC conduit, "Underground". OTOH I do not separate control cables (six
pack, remote antenna switches, or rotators) from coax, or even satellite
TV coax to the receiver. The network cables OTOH run in their own
conduit along with the telephone line, BUT in the shop there are 3 CAT6
and one telephone twisted pair right in there with the rest of the
cables. Both quad core, 3.4 Gig computers are within 3 feet of the
station with one having its serial port connected to the C-IV interface
to the one QRO HF station The 75 and 40 meter antennas run almost
directly over the network cables, but nary a peep. The coax to the
Diamond 144/440 antenna runs within feet of the network cables and the
antenna is about 45 feet almost directly over those cables. Nary a
sound on any band, BUT take an HT into the back yard and that network
will drown out a 5W HT at the top of the tower with me nearly 100 feet
to the West.
> having the end of your 80 meter
> dipole located just over the roof above your shack might result significant
> unwanted signal coupling.
I thought that was a problem, but it turned out to be common mode on the
75 meter feed line. I put a choke where the coax reached the tower and
the problem went away. It also let me cook the W2AU balun on the
antenna which I had planned on replacing with a current balun anyway.
Just not so soon.
> The same thing can happen when routers or cable
> boxes are located in attic areas or second stories of houses and there is a
I should mention my degree and field are in CS so I'm very intolerant of
any malfunctioning computer or network equipment.
Routers or cable boxes are on the "return if a problem" list. Any new
piece of network hardware, router, modem, switch gets returned
immediately if there is a hint of a problem. To me, these are definant
replace before trying other methods, equipment. That is along with most
other new hardware for the home such as TV sets, washers, dryers, or
what ever I can think of. There is one exception. I absolutely refuse
to use anything made by Sony unless it sneaks in as a component inside
something like the sensor in my camera.
I have about an 8' length of 8X with a probe end about 6" long. I hook
that to either the yaesu 897D or the Icom 7000 and run it all over the
new pieces of equipment. If I can't hear it more than a foot or two,
it's fine. I picked up a new 40A switch mode PS. I can't hear it with
the probe laying on the case, nor can I hear a peep out of either
computer right next to the rigs in the shop. Right now the big computer
with the 300 watt plus video card that sets right next to the rig has
both sides off and three HDs are setting on the floor.
BTW all lights in the house are either CFLs or fluorescent. The shop has
22 8' 75 watt tubes. I did hear one ballast when it failed.
> 40 foot tower adjacent to the house with a tri-band yagi and a couple of
> inverted-Vs on it. Sorry - you might lose the RFI battle on that one.
> I agree with Jim's comments: if you must do something, do it to the cables
> and interconnects.
My first step is "return it if I can" (That means if it's new it's going
back. I only purchase this kind of stuff locally even if I have to pay
more for that privilege), try replacing it if I can't, if there is still
a problem, THEN work at eliminating the problem. I've gone through many
routers, but my previous one was nothing more than a bare circuit board
laying on the desk. It led a rough life, but it worked great.
Unfortunately I started getting disconnects across the network and from
the internet which I traced back to the router.
I belong to the camp that says, "If it's not working right, replace it",
or throw it out.
If I have a modem, router, or switch that goes bad out of warranty, I am
not even going to bother trying to eliminate the problem before
eliminating that piece of equipment. I'm not going to try to fix it as
even top level routers, switches, or modems aren't worth my time trying
to fix them.
> If that is not enough, try getting more separation
> distance between the source and your antennas. It might not be easy, but
> that's still better than trying to modify a piece of equipment that is
> actually designed just fine (met its specs when tested), but you are trying
> to make it work to a requirement that is more stringent than the design
> specs intended.
Buy with a try policy.
> There is one instance in which taking action against the equipment might be
> practical: high noise power supplies, expecially wall warts.
Again, those are not worth the effort. Just pitch 'em. I have boxes of
the things in the shop. If one goes bad I can have a replacement in less
than 5 minutes. Yes, they are one of the few things out there I can
still walk right up to and grab. The things I put where I would be sure
to find them (wehre ever that was) far out number the ones I remember.
> I have
> personally seen wall wart supplies (using switchmode technology) in which
> there are parts missing from the pc card within. You know the story: the
> parts are all there for the required FCC or CE test, then the production
> runs leave out those EMC-suppressing parts to save costs.
Or it just gets missed on the assembly line. QC on some of this stuff
is close to non existent.
> That's very
> common with some 3rd party "no name" warts from the Far East. Since you
> probably can not get information as to just what the values of those
> missing parts are, the most practical approach seems to be to find either a
> linear power supply (bigger, heavier, less efficient) with the required
> output, or a switcher that actually has all of the parts and does meet
> specs. Good luck. I endorse Jim's "bucket treatment" for the offending
> pieces of trash.
I think Jim's bucket treatment is the same as my trashcan treatment<:-))
It's just I'm quicker to resort to that route and probably on larger
> 73 and Best New Year Wishes to everyone,
It appears we may start out the New Year with W-A-R-M weather! Maybe
even some sun Saturday afternoon and temps in the 40's. Hopefully
without fog. It's time to get the rust out of the engine in the old Beech.
> Dale, WA9ENA
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