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MFJ 931 Artificial Ground - Icom IC-R75

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oceans777

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Same sad story - in a 4th floor apt, no possible way to ground my IC-R75 for HF use and lots of noise on the bands.

Has anyone tried or is anyone currently using the MFJ 931 Artificial Ground with an IC-R75 or HF receiver?

http://www.mfjenterprises.com/products.php?prodid=MFJ-931

Does/will it reduce noise?
I read the manual and it seems to electrically balance a counterpoise wire you would run around the floor if no proper ground is possible. It states that this reflects RF energy back into the antenna and increases signal strength - but my antenna is usually a thin wire hanging out of the window.

Experiences\thoughts appreciated!
 

mass-man

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I used the MFJ artificial ground MANY years ago living in an apartment. My understanding of the unit is that is is really for providing a counterpoise for transmit antennas, and will probably do little for receive. My situation finally forced me to operate at low power levels and then I had no stray RF running around my radios...this was long before computers.

You might try a ground wire to the middle screw on a wall plate...but I doubt the investment of the RF artificial ground is going to do you much good.

73's...cleve
 

ReceiverBeaver

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Hey guy,

The noise you're getting on HF is most likely combined atmospheric static from lightning. Whatever band you're on anytime of day, you're getting a mishmash of local lightning static crashes plus the static of every lightning bolt in the area that the band you're on is open to.

Summer = noisy

Winter = much quieter to zero noise

These are only typical scenarios. Other things such as power lines, the welding shop down the street, electric fences, computer monitors, plasma tv's ect....blah blah blah can cause and add noise.

Grounding systems and schemes have little to no effect on received noise levels.

Try a decent outboard Digital Signal Processing unit or something like that. May help.

Good luck
 

oceans777

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Thanks for the info - I have a better understanding of it now.

I wondered if much of the noise comes from living only a few miles from Mt. Wilson - more broadcast and various commerical antennas there than you can count.

Using a Dressler ARA100HDX now and it does remarkably well most of the time - even four floors up and indoors. Move it outside and noise goes WAY up with no signal gain.
Also a wire just hanging down the building about 3 floors - this is quieter and better signal much of the time but for some reason goes deaf after sunset - even in the lower HF bands.

I will check out the DSP options - thanks!
 

ReceiverBeaver

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Hi Mass Man,

I've never needed to use one, an outboard that is. My ham rig has internal dsp, a feature becoming more and more common.

The models made by Timewave seem to be popular with the ham crowd. You see them at the usual ham places like Ham Radio Outlet, Amateur Electonic Supply ect....
 

ka3jjz

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To borrow an 80s phrase - I feel your pain. I live in a 3d floor condo, no way to directly ground anything at all. I had been reading some articles on how magnetic longwire baluns sometimes help cut noise down; I had a 4:1 balun in an old MFJ tuner, so I said what they hey let's try it and see what happens.

My noise floor dropped probably by about 20% or so.

I've also built a smaller version of the carpet loop (the plans are in the wiki) - far less expensive than getting a Wellbrook or similar. Only used a 20 foot loop just as an experiment, and the results are interesting - sometimes it's quieter, other times the random wire through the balun is quieter.

Some products and information on using MLBs, coax loops and other items are in the wiki. The PAR antenna is very highly regarded, and would be worth a look. So would building a carpet loop, or the 50 foot coax loop that's on one of the links (many rooms can easily fit this, providing that it's strung properly). The Shortwave antennas Yahoo group has plans on how to wind the toroid for a simple transformer, and has other low noise ideas, such as the Snake antenna.

This of course assumes you've done your homework and filtered, trapped or otherwise have taken care of noise sources in your apartment - you can't do anything about the neighbor turning on the water heater for his fishtank (arrgghhh...) but at least your local noise sources will be addressed.

73s Mike
 
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kb2vxa

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Hi EO7 and all,

That "artificial ground" is useful only for providing a counterpoise for transmitting much the way an antenna tuner matches the feedpoint impedance to the 50 ohms of the transmitter output. In effect it "tunes" the ground wire to reduce reactive effects.

Your noise problem will not be solved by any sort of grounding and in fact grounding to the electrical system may actually increase noise since that's where much of it comes from. The lion's share comes from appliances in the building and while some is radiated some is transmitted throughout the wiring and some of that is radiated BY the wiring, you're living in an RF sandstorm. If you ground at all a cold water pipe is your best bet but like a boat it's any port in a storm, my only station "operating ground" is the baseboard heating pipe. No, it's not for noise or RF, it's forsafety but it's a path to Earth just the same.

The obvious solution is an outside antenna, ANY outside antenna preferably some distance from the building. OK, you have to kowtow to management so the word is STEALTH. There are limitless ways you can conceal or disguise an antenna so being it's WAY beyond the scope of discussion you'll have to do your homework and then use your noodle. Hams have loads of experience in putting one over, your best bet is parsing the related web sites, everything is there and you don't need to ask and get the same answer I just gave.

OK, go ahead and ask but AFTER you have gathered some information to go on, a good place to start is www.southgatearc.org which already has several articles published on stealth antennas. One I remember is hanging a wire out the window of a high rise somewhere in London but it'll work just as well in Los Angeles. Another great site is www.qrz.com so ask the guys where you can find published articles on the subject before you ask questions that beget tons of useless answers, get some ideas first and be specific.
 

gcgrotz

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Hi E07 and Warren:

I have a noise problem on my small city lot, some is from all the sodium and mercury vapor streelights all around. I ordered a PAR and am hoping as I write this taht UPS shows up before my wife gets home so I don't have to explain it! I'm looking at the MFJ antenna phasing noise cancellation box if the PAR doesn't help, I've heard great things about them. All the AM Dx'ers use them.

As for cold water pipes, be careful. I've seen buildings all plumbed nice and pretty with copper and it all looks good down to the main cut-off where it connects to plastic. This just makes it a big counterpoise and noise picker-upper.

DSP units do help, does your R75 have one? If not, get one. Mine would be intolerable without it.

Still waiting on UPS, HURRY UP MAN!!!!
 

kb2vxa

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Hi Grotz and all,

HPS and HID lamps are seldom a problem except during the short start cycle. Naturally when one goes bad and tries to start over and over it gets worse, then tell the power company the pole number and if they're worth anything they'll get around to replacing it before it craps out entirely.

The easy way to tell if the plumbing goes to ground is the ohm meter. Since the power neutral and protective ground MUST, there should be continuity between them. If the neutral bus connects to the water lateral the meter and any plastic MUST be bridged but that's no guarantee some plumber hasn't used plastic elsewhere. Still if the metallic pipe is continuous you shouldn't get more than a few ohms between the pipe and the electrical ground even if the electrical ground is separate, that is connected to an earthing stake.

I have no idea what a "PAR" is besides some brand name but I'm assuming it's similar to that MFJ noise canceller you mentioned. I never tried one but the theory looks good, the RF version of the tried and true IF noise blanker. If it gives similar results it'll beat the hell out of audio DSP, the phase cancellation works best at the IF. Still if audio is all you have to work with like most of us a DSP unit sure saves us (me) from going nuts and suffering ear bleed. The worst drawback is it does nothing for the all important S/N ratio, AGC action will still bury the signal, even MGC (turning the RF gain down) won't help. Still without DSP I wouldn't waste my time with HF from this location, maybe with a bit of luck I'll eventually move away from all this high voltage and neighbors having crappy consumer electronic noisemakers.
 
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