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Author Topic: MFJ- 1026 VS MFJ-784B  (Read 2925 times)
N5YPJ
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« on: August 10, 2008, 01:26:28 PM »

I am somewhat confused as to what would be the better solution to get rid of some of the noise here and hopefully dig out a few weak signals. Both units seem to give the same results, unless I am misunderstanding something. I just wonder what is the best bang for the buck the MFJ-1026 1.5-30 MHz Deluxe Noise Canceller or the MFJ-784B Deluxe Tunable DSP Filter?

I work mainly digital modes and use a trap vertical antenna. We live in the country,have three computers with wired router, numerous wall warts, there no doubt is some power line noise then there is an industrial park about 5 miles down the road over in Mexico. Nearest neighbor is about half a mile away.

Any opinions ?
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KB9CRY
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« Reply #1 on: August 10, 2008, 06:05:01 PM »

Any opinions ?

Separate receiving antennas are the way to go.

Electronics may help sometimes but not all the time.

You have a vertical antenna which is vertically polarized and picking up manmade noise which is vertically polarized.  Try a simple low dipole on your band of choice for receive.  You'll be surprised.
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N3OX
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« Reply #2 on: August 12, 2008, 06:48:32 AM »

I think you might be disappointed with either product if your expectations are high, though I haven't actually tried the '784.

The MFJ-1026 works for what it's good at, but it's a bit technical to get it to work right, and by the time you get it to work *well* you often might as well have fixed the problem at its source.

But it can do two things... it can null out a noise in your own house pretty easily... you just need to put up a noise antenna that hears the noise signal very well without hearing your desired signal much and you can make that noise vanish.  It's almost like magic... tricky to adjust magic, but magic.

Unfortunately, the "right" noise antenna for me has always been different on every band, and the noises come and go and change relative phase enough that I very rarely find it worth using the canceller.  For a while I had some awful noise on 20m and 17m from a neighbor's electronic device of some sort, and it was nice that I could get rid of that when I was pointed south or southwest where it was bad.

- - - - - - -

But here's the problem... if you get more than a few wavelengths away from the source, you're often going to need a very similar antenna to your main one to give you your noise signal... and that means you're going to end up a real phased array.  You can  successfully null out directions this way, your Mexican industrial park noise might go away, but you're basically going to have a NULL in that direction for ALL SIGNALS ...

Maybe that's OK for you, but it killed the utility of the device for me here.  When I tried to use my MFJ-1026 for the reason I bought it, which was nulling out the noise from some elevators on 80m in an apartment building northeast of here, I succeeded but would also null out the desired European and Middle East stations!

You can use different polarizations to alleviate this somewhat, but when I tried to use a horizontally polarized noise antenna, it barely picked up the elevators and it *strongly* picked up some power line noise... so I could not really null the elevators with it, and even if I had, the power line noise would be mixed in.

So all in all, the MFJ noise canceller actually works but it works in a way that makes it seem like it doesn't work to many folks who try it out.  It might cancel some of your house noises, but so would ferrite cores on all the electrical cords, which is a more direct and easier solution, probably.  

As far as DSP goes, you might try it, but it'll probably just make the noise more pleasant to listen to, not really get rid of it (noise is a signal, after all), and I have to wonder if your digital decoding software would care one bit... I'm not sure it would.

My audio DSP in my FT-857D isn't the greatest in the world, I'm sure, but it blunts the edges of some noises enough to make it worth turning on the digital noise reduction... but it doesn't make a bit of difference on copying PSK... in fact, if anything, it makes copy worse but I haven't been able to test that rigorously.

73,
Dan

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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
WA7NCL
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« Reply #3 on: August 12, 2008, 07:59:27 AM »

The add on DSP will not help much.  The interfering signal will already be demodulated and capturing the AGC.  Your only hope is the phasing device subject to the limitations the other poster stated.

I agree with him that, if possible, locating the noise and eliminating it is the best course.
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N5YPJ
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« Reply #4 on: August 12, 2008, 08:13:53 AM »

I'm doubtful of the DSP unit, IMO once the noise gets in the IF stage it's there - the better solution IMO is to get the noise before it gets to the radio. I read a lot of good reviews on the DSP, it sort of surprised me that many people found it that effective. Not saying that it doesn't work but questioning it's principal of operation.

Anyway - can anyone tell me what the MFJ-1026 will do (if anything) for atmospheric noises? I can live with phasing out the industrial park it's due south of me and not much signal coming from south.
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K8GU
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« Reply #5 on: August 12, 2008, 09:12:19 AM »

The reason that DSP doesn't work well with PSK is that PSK is a DSP mode already designed to be received in low SNR conditions.  There's simply not much more an external DSP can do for you.

Will the phasing box help against atmospheric noise?  Well, again it all depends on how your system is configured.  If you're using it to pull a null in the direction of a thunderstorm, then the answer is probably.  But, if that T-storm is between you and the DX, it might not be so useful.  As Dan says, you can't just plop it into your system and expect miracles.
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