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Author Topic: Running an amplifier in a typical suburban neighbo  (Read 273 times)
W8JJI
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Posts: 291




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« on: January 07, 2003, 06:40:41 PM »

 I am considering getting an amplifier for the ham shack. I am considering an amp of either 500 or 1000 watts output for the HF bands. I am concerned with rf interference to the neighbors around me. I realize that properly grounding the equipment in the shack is the first step in reducing rfi troubles, but my shack is on the 2nd floor. Not the best for a good ground. Or does that not matter when your talking about rfi ?  At my location the neighboring houses are about 23 feet apart , gutter to gutter. At a 500 or 1000 watt level of output is it possible to operate without bugging the folks next door or my own family with rfi ? My antenna is a vertical on the center of my roof. Has anyone out there had any sucsess in a similar situation ? Or maybe I should just forget about using an amp completely. Thank you for your input.---W8jji
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WB2WIK
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Posts: 20547




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« Reply #1 on: January 07, 2003, 06:51:05 PM »

When I first saw your callsign, I thought your question was a joke, as you're only one letter away from a well-known amplifier designer (W8JI).

Anyway, there's surely no substitute for "distance" when it comes to avoiding RFI -- the farther your antennas are from all other appliances, the better.  But your situation sounds pretty typical, and not much different from mine (1/4-acre suburban lot), and I have *no* earth grounds of any kind, and run a kilowatt on many bands without any RFI in my home or any of my neighbors' homes.  But that took some work.

If you recall the movie, "The Graduate" from the late 1960's, you might remember Dustin Hoffman's character got a single word of very good advice from one of his father's friends (I think).  The word was "Plastic."

Today, I use another single, magic word: "Ferrite."

With enough ferrite chokes and bypass capacitors, nearly any RFI problem can be solved, with or without earth grounds.  In my case, I'm using more than 100 ferrite clamp-on chokes all over the house (telephones, televisions, VCRs, DVD players, Nintendo games, alarm systems, smoke detectors -- you name it!), and I've spread the wealth to some of my neighbors as well, solving any RFI problem that raised its ugly head, one by one.

I also use ferrite line isolators in my transmission lines, and ferrite cores over my amplifiers' AC power cords, to help minimize conducted emissions through the line.

It all worked, and I'm totally RFI-free, at >1 kW output, any band.  But "ferrite" was certainly the magic word, for me.

If you have zero RFI problems now, with 100W, I wouldn't expect you to have severe problems with 10 dB more power.  Some problems, likely.  But hopefully not severe.  If you have RFI problems now, with 100W, I'd get those solved first, before adding the amp.

WB2WIK/6
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AC5E
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Posts: 3585




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« Reply #2 on: January 07, 2003, 07:46:43 PM »

HI Richard: As Steve says, there's no substitute for distance - from the point RF is radiated to a device that might suffer interference. It helps mightily if you can keep your RF confined until it gets to your antenna.

100 percent shielded coax helps a lot. Especially if it's 100 percent shielded CATV cable to the neighbors TV! And it's solid with no leaks. You can test the situation with an HT, tuned to 145.25. If you can hear a continuous carrier - the CATV cable leaks out and if you run a lot of power your RF may leak in.

Fortunately, if you have an HT it's usually pretty easy to run the leak down;  and something as simple as tightening an F connector or the lightning arrestor's ground screw is often enough to solve those problems.

An RF ground can help. Just running your coax through a solidly grounded lightning arrestor (at ground level, of course) can sharply reduce unwanted radiation.

So can a current balun (look at www.radioworks.com for more complete information than we have room here for)
at the feedpoint of your antennas. And on the shack side of the lightning arrestor.

And of course, there's no law that says you must run that legal limit amp at full output. I usually let the Alpha and the Titan loaf along at 500 to 700 Watts out.

With all that - my experience with handling a TVI complaint? I have had one in the dozen years I have been hamming from my house. I came back from a month's vacation, had just set down to sort the mail into bills and junk, and the woman next door called. To tell me that she had tried to talk to her best friend every day for a month and every time she got on the telephone my blankety blank ham radio drowned her out.

And I said "Lady, I haven't been home for a month." Which put an end to that.

73  Pete Allen  AC5E
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N8FVJ
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Posts: 692




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« Reply #3 on: January 07, 2003, 09:09:05 PM »

To get a head start on this amplifier project, I suggest tube type. The tubes make use of a high 'Q' tuning network reducing out of band harmonics.
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WB2WIK
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« Reply #4 on: January 08, 2003, 10:49:08 AM »

Pete, once, in about 1978 when I had just purchased a new home in New Jersey, the first thing I did was install a tower and some antennas -- weeks before moving in.

My neighbor across the street, an older woman, came over when she saw me in the yard stringing an 80 meter dipole, and complained that ever since I started with my radio gear, her refrigerator wouldn't defrost properly, and it was all my fault.  At this point I had no equipment there, and hadn't run the coax yet.

The only thing I could think of to do was get very close to her, and say in a very hushed voice, "You know about that, eh?  Don't tell anyone else.  I'd like to tell you what I'm doing here, but I cannot.  Top secret.  Be on your guard."

Or something to that effect.

She went away happy, knowing some top secret information that nobody else knew, and I never heard from her again.

WB2WIK/6
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AC5UP
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Posts: 3825




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« Reply #5 on: January 08, 2003, 11:40:14 AM »

You do realize that no matter how clean your station is, you will have a neighbor or two with an ultra-cheap TV, stereo, cordless phone, baby monitor... etc... And, that no amount of techno-babble will make them love you like a brother.

Avoid punching full power during normal waking hours, and remember the first 3-6dB of amplification has the most effect on the receiving side. Anything beyond that is probably just bonus income for your power company.

- AC5UP
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