QRZ! Ham Radio 11/QRZ Ham Radio Callsign Database - Volume 11.iso/files/library/rfi_tips.txt

Text File | 1998-02-02 | 5.9 KB | 126 lines

>Path: news.unomaha.edu!sol.ctr.columbia.edu!usc!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!ames!olivea!news.bbn.com!noc.near.net!uhasun!arrlhq!ehare
>From: [e-mail] (Ed Hare KA1CV)
>Newsgroups: rec.radio.amateur.misc
>Subject: Re: Ham Radio Interference from Neighbor
>Message-ID: <[e-mail]>
>Date: 7 May 92 15:40:01 GMT
>Sender: arrlhq!ehare (Ed Hare KA1CV)
>Organization: American Radio Relay League
>Lines: 115

I received a personal email request for advice that I thought I would
share with the net. After this I promise I will shut up about EMI/RFI
for a while. :-), Ed.

To: uhasun!nvuxr.cc.bellcore.com!karayan
Subject: Re: TVI blues
Message-ID: <[e-mail]>

>I saw your latest posting in netnews on TVI and what the ground
>contributes to it.  Finally!  Somebody understands me!  People keep
>telling me that I need to find good ground, etc.  However, I live
>in a 2nd story apartment.  The grounding path will go from my livingroom
>(where the rig is) to the kitchen (cold water pipe) and down, through
>the 1st floor and basement, to the ground.  If this path doesn't
>radiate like crazy, I don't know what will.

It sure will!

>Soooo, I am running my rig into a balun, flat-ribbon feedline and
>to a 15m folded dipole.  Everything is balanced after the tuner.
>Otherwise, my ground is floating -- nothing connected to the lug.
>Do you see any problems with this arrangement?

Not from an EMI standpoint. There are safety considerations that I will
not get into here.

>Nevertheless, I have TVI problems galore!  I haven't been all that
>successful getting out with the indoor antenna, but my two TVs get
>me just fine!  I assume that the house electrical wiring picks up
>RF from the antenna and feeds it to the TVs.  Am I right?  Would
>power-line chokes correct the problem?

I think I would try the "standard" TVI remedies. Contact your section
Technical coordiator (located through your Section Manager - page 8
of QST - or ARRL HQ.)

* Install a low-pass filter between the transmitter and the antenna tuner.
If the TVI is on channels harmonically related to 15 meters, ie channel
3 and channel 6, this will probably be the cure. Even if not, put it on
anyway. The TVI might stem from both station harmonics and fundamental
overload. This way you will be confident that it is not your station.

* Purchase some FT140-43 ferrite cores. (#43 is the material of choice for
15 meters. If you also operate on 80, get some FT-140-J, FT-140-75, or
FT-140-77. If you have RG-8 (or equiv size) cable, or a BIG line cord
or plug, you may need to use an FT-240 size core.)

* Wrap about 10 turns of the transmitter's AC line cord around one of these
cores, as close as possible to the transmitter. This is a common-mode choke.
(If you have other AC-powered equipment connected to the transmitter, ie
keyer, SWR meter, TNC, etc, install one of these on its AC line cord, too.
The idea here is to prevent any chassis RF (harmonics or fundamental) from
seeking earth via the power lines.)

* Do the same thing with the coax cable between the tranmitter and the tuner.
This is also a common-mode choke.

* Now you know that the transmitter is (probably) clean.

* Simplify the TV installation. Multiple TVs, VCRs, etc make it impossible
to troubleshoot. Get it down to one antenna or cable and a TV. If it is
cable and a non-cable-ready TV, use the set-top converter or VCR as you
normally do. After you get the bugs out, you can start adding stuff back
one at a time.

* If you have a TV preamp, booster or distribution amp, get it the heck out
of there. These things are notorious for overload.

* Install a high-pass filter on the TV (or before the set-top converter/VCR.)
If using a set-top converter/VCR, you may need to use one before the converter
AND before the TC.)

* Install a common-mode choke in the same location(s). If the TV is using a
CATV or community antenna, I would try the common-mode chokes before the
high-pass filter, just to play the percentages.

* Install a common-mode choke on the TV and set-top converter/VCR AC-line
cords.

* If you still have interference, try using a differential-mode AC-line
filter on the TV, set-top converter or VCR, and the station transmitter.
Radio Shack catalog 15-1111 is universally available.

* If you still have TVI, either you have one of those "wierd" problems
that you don't even want to think about, or you have a TV that is just
so susceptible that it can't be helped. If so, call me here at HQ. I
will offer some advice. But please, read the RFI Tips handout and the
Radio Frequency Interference book before you call me. I don't mind
helping, but would prefer that we not have to cover the basics.

>Needless to say, I have not advertised that I am a ham and I operate
>in the deep dark of the night.  No wonder I'm getting nowhere; that's
>when 21m is dead.  Any advice?

Yeah, move! Actually, the best solution is to clean up your own house.
That may take care of everyone's problem. If not, at least you can demonstrate
that it is not your equipment. Do be careful, though. If you mishandle the
situation you may find yourself having to buy a few hundred ferrites, high-
pass filters, etc. You are not bound by law to purchase any filters to
compensate for inadequate filtering in consumer equipment. Some hams
take the easy way out and pay for the one filter needed to help one
neighbor. You probably can't afford that luxury.

>I would appreciate any pointers, Ed.  Thanks in advance.
>George, N2OWO

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Ed Hare, KA1CV                  | [e-mail]
American Radio Relay League     | uhasun!arrlhq!ehare
225 Main St.                    |
Newington, CT  06111            | There is no limit to what you can
[phone] - voice          | accomplish if you don't care who
Senior ARRL Laboratory Engineer | gets the credit. - Harry S Truman
RFI, xmtr and rcvr testing      |
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