All,
This has become a very interesting thread. I would like to add a comment
about one more aspect of EMI control: separation of source and victim(s).
I noticed that Peter, WB3FSR, mentioned he has a roof-mounted tower on his
house. I had a similar situation at my former home in Illinois (but using
tripods and an eave bracket, rather than a tower), where I was strictly a
roof top antenna farmer. Out here in Iowa there is room enough at the new
QTH to spread out and position most antennas well away from the house, but
there are so many things for us (myself, and Sue, KE9LI) to do at the new
place that the towers are not yet installed. So, we have been running with
temporary masts (of the Fair Radio surplus variety) set up in the back
yard, and some RS masting on the back deck, as our interim antenna
supports. The results: not much better than when it was all on the roof
because the radiated fields are still close to the victims (TVs, stereo,
telephones). I have decided to wait with the "ferrite patrol" duties until
the antennas are in their permanent locations, then attack each victim on a
case-by-case basis. Luckily, we have not had RFI from any of the devices
into our radios.
I have been gratified to see that the close RF fields have NOT affected our
Rheem high efficiency heating/cooling system and its associated
microprocessor t-stat. I do hear a short "machine gun static burst" on HF
(especially 80 and 40) when the furnace igniters fire, but that is so brief
a time as to not be any problem at all. Otherwise, the system is RF
"clean" and does not react when I transmit on any band 80m thru 70 cm (6m
and 1.25m excluded, as I have no gear for those bands at present).
We ran all of the house telephone wiring ourselves, and we also have 5 of
the 500-type tel sets ready to go if and when I encounter any sleaze-ball
electronic ones that can't/won't be calmed by beads. (There did not seem
to be any point in placing beads onto the wall wiring, as most of the desk
phones have cords that are long enough to render the beads ineffective.
When the antennas are eventually relocated, I might try the large beads
directly at the jack for wall-mounted sets only.) Our cordless phone died
recently (it was a 49 MHz type that did not have significant problems with
RFI once I placed a bead on the base unit's line to the wall jack), and
after reading about so many problems with the various 900 MHz and 2.4 GHz
ones, I am still thinking about which one to buy as a replacement.
(Attention homebrewers: if you have a 49 MHz cordless that croaks, you
might check the guts before dumping it to see if there is a Motorola MC335X
or MC336X-series chip (or chips) used in the receiver. You might be able
to make a 6m FM rcvr for monitoring 52.525 or a nearby 6m ham repeater with
the chip and a little re-work of the circuits.)
When faced with the prospect of not being able to increase the distance
between source and victim, the bottom line is less RF power on xmit and
better suppression in devices that unintentionally radiate and/or receive
(Part 15). The choice of antenna can help, too, as some types may be able
to provide a null in the direction of the victim device. (Granted, that
goes way when you rotate the array, but some help may be better than none.)
If someone uses a vertical omni ground plane for VHF/UHF FM, note that many
antennas of that type will have a null notch directly beneath the antenna.
(A good example is presented in Bill Pasternack's [WA6ITF] book, "FM and
Repeaters for the Radio Amateur" [or similar title], published around 1979
or 1980, and now probably out of print.) Assuming that a TV is connected
to cable (no outside antenna) but is affected by VHF/UHF operation,
locating the omni (as high as possible) directly over the victim set may
help. Emissions from the TV set should also be reduced in amplitude at the
antenna. (There are some nice charts in Pasternack's book that show
isolation vs. distance in the horizontal and vertical planes. The examples
given are for isotropic antennas, but the data can still provide an order
of magnitude guesstimate for what you might expect. The information on
the null beneath vertical omni antennas is for "real" antennas, not
isotropics. I am sure that other reference sources give similar - maybe
even better - data, but that is one I have used for years in quickly
estimating close range isolation issues. You can also use the field
calculation models available for the computer to make accurate predictions,
but a good reference chart is tough to beat for fast reality checks.)
Best luck.
73, Dale
WA9ENA
"EDWARDS, EDDIE J" <eedwards@oppd.com>@contesting.com on 09/04/2001
09:41:37 AM
Sent by: rfi-admin@contesting.com
To: "'wb3fsr@home.com'" <wb3fsr@home.com>, "'RFI'" <rfi@contesting.com>
cc:
Subject: RE: [RFI] Sony WEGA RFI Problems
> -----Original Message-----
> From: Peter D. Vouvounas
> We have four TV's in our home with
> Microwave video / audio distribution - 3 of the four sets are Sony and
> none
> of them except the XBR appears to cause any problem on HF.
>
That's interesting. Must be something in the XBR's design.
Something fundamental for it to be in the design this long!
> Ed- When the XBR is opened up what are your recommendations for ferrite's
> on
> the internal speaker wires???? Did it help / how many turns, anything
> special I need to know?
>
On my XBR, the audio rectification was tremendously loud. Ferrites
on all cabling on the outside only reduced to to mildly loud. When I
finally got up the gumption to crack her open and try internal ferrites, I
was glad to see the audio board had PCB connectors on the speaker wires and
PLENTY of wire as well. That was probably a contributing factor --the long
unneccessary excessive length of speaker wire-- but it helped for making
the
RFchoke. I put over a dozen or more turns on the square Rad Shack ferrites
and the audio rectification was completely gone! Wife was happy, kids were
happy, I was contesting again!
Don't know about the new case design but the old one was really
flimsy for how heavy the TV is. Very difficult to pull apart without it
falling all apart.
> When I fire up my big amp "EMTRON" with the GU84B it drives my powered
sub
> woofer nuts. I was not too surprised by this. Simple resolution is to
> turn
> it from auto power on to off hihi. Haven't installed any ferrite's on
> this
> beast yet.
>
I gave up on my powered sub-woofer. I run my audio through my
EMI-clean sound system so the sub woofer was redundant anyway. It'll
probably take internal ferrites to clean it up. Nothing external worked on
mine.
> I'm still dealing with my 2-line GE phone in the shack/office that totals
> out from a 1/4 watt VHF/UHF signal much less HF at any power. The trick
> here is to find good RFI proof multi function phones for the upstairs. I
> don't believe my wife (N2THE) would accept standard 500 set type phones
as
> replacement. One company that I checked on for RFI proof phones was
> offering the 500 style set about a year ago. In my home probably similar
> to
> others you don't mess with the XYL's phone or she'll cut my air-core
lines
> to the antennas hihi. I'm not kidding!!
>
Good luck. Multi-function phones can be a nightmare, but look at
your house cabling to map it out. It might need re-routing to shorten runs
or keep them from being routed near your antennas. Otherwise, ferrites &
chokes, ferrites & chokes, sometimes I wish the stuff would just smoke!
I'm glad my xyl (KC0DXi) is afraid of my cables & stuff!
73,
de ed -K0iL
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