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Author Topic: Filter or Noise Canceler?  (Read 891 times)
AD0AE
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Posts: 79




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« on: January 23, 2013, 09:46:15 AM »

Hi All-

I have been debating a little bit about what might be a good 'long term option' to the noise problem I am having at my apartment.  Just to give some basics: I have an IC718 using indoor antennas (I live in an apartment and I can't put anything outside- so don't bother suggesting that).  On any day, I have around S9 level noise that I am receiving, along with whatever I am trying to listen to.  It would be nice to knock the noise floor down, if possible.  I can tell you that I have many power lines hanging outside, a power transformer within 50 feet of my transceiver, and many other house/buildings close by(including a retirement home across the street!).  I will also mention, I have tried to put some outdoor antennas outside and the noise is about as bad out there as it is inside.  I will openly admit that having a high noise level has been a benefit at times - particularly that it can 'preselect' some of the people banging away on JT65.  

That being said, I have read a bit about the mfj 1025/1026 noise canceler and also been suggested that getting some SSB or CW filters might be a good way to knock down the noise floor.  

Question: Given that the cost is approximately the same amount, and given that I can probably afford to get one, at some point, in the near future, I am wondering which might be a better option both in the short and long term?  

Are there plans online to make fairly simple, effective, filters for the ic718 that would be easy to install?

 I may be apartment hopping for another year or two depending on where I land a postdoc/how much I get offered/how expensive property is.

73s all
Steve
AD0AE
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AD4U
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Posts: 2180




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« Reply #1 on: January 23, 2013, 10:52:24 AM »

Steve - I seriously doubt that ANY noise canceller will help you at all, no matter how much it costs.  Maybe "one day" DSP will be able to differentiate between unwanted noise and the desired signal, but I do not think that day has arrived.

From the description of your conditions, I think you just live in a very bad location for receiving HF signals.  The inside antenna only makes things worse.

Sometimes there is just not a good answer to a problem, and I think this is one of those times.

Sorry.......

Dick  AD4U
« Last Edit: January 23, 2013, 10:55:59 AM by AD4U » Logged
WB6BYU
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Posts: 13489




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« Reply #2 on: January 23, 2013, 11:02:15 AM »

How well either system works will depend a lot on the source and type of the
noise.

A noise canceller works well when noise is coming from a specific source, and
particularly when you can position the noise antenna to maximize noise pickup.
If instead the noise is being radiated from multiple sources or locations (for
example, along a power line) then you might not be able to get a null.  The
same is true of various types of receiving loop antennas (which can also
couple to the building wiring.)

Some noise types, such as power line noise, that have a specific base frequency
might be handled well by DSP, but other types won't.

A narrow filter will improve the signal-to-noise ratio by picking up less noise in
the receiver passband (as long as it can still pick up the whole desired signal)
but doesn't make a huge difference on, for example, and SSB signal where you
still need a minimum bandwidth.  Helps a lot with CW, however, since the signal
is very narrow.

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KC1MK
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Posts: 24




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« Reply #3 on: January 23, 2013, 11:15:00 AM »

I use an MFJ-1026 noise canceler at my QTH with good results. More often than not (usually unless it's raining or just rained), there is heavy powerline QRN, but no other noise problems (I live at a semi-rural QTH). Once I experimented with noise pickup antennas and got one that worked well (in my case, a G5RV at about eight feet), the MFJ unit usually completely eliminates the noise. Occasionally it won't eliminate the noise completely, but knocks it down to a pretty low level. Without the MFJ, I often am unable to even hear, much less copy, an S7 or even S9 signal. Basically, my receiver would be useless most of the time without the MFJ. I have repeatedly contacted the power company. They come out and tighten connections, etc., with little or no result.
If there are multiple noise sources, you're probably only going to be able to eliminate one at best.
DSP filtering, and even a noise blanker, are probably only going to provide minimal results if the noise is severe.
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KB4QAA
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« Reply #4 on: January 23, 2013, 11:15:11 AM »

There is no 'cure' for multi-source QRM in close urban/suburban environments.

Both approach will help in different ways but neither will eliminate the noise from your radio.

Filters are always an excellent decision, and in my opinion a necessity for anything more than casual occasional operating.  Looking at the product sheet I see a 1.8khz SSB filter (a bit narrower than my preference, and can be tiring to listen at length, but good and tight).  The 500 Hz CW filter is fine, and is useful for data modes. not as tight as the 250hz for CW work only.  Your choice.   Filters make operating much more pleasurable (tolerable)

I'm not aware of any difficulty installing Icom filters.  Get help or send it to one of the shops.

I've have a 1026 (both essentially the same).  At times it can help tremendously, but it is not simple to operate, it can only work on one signal at a time, requires a second antenna (however simple).  And it's effectiveness varies depending on the antenna setup, signal type, signal distance, and has minor limitations inherent in the design and complexity level.    (It's a fascinating device, worthy of study and further development).

Summary:  
-I always put narrow SSB and CW filters in my radios.  
-Long term, when you have money, and get into digital/Oscar work, install a TXCO
-The only way to reduce noise is to move further away from other people

good luck, bill
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W8JX
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Posts: 6482




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« Reply #5 on: January 23, 2013, 11:25:09 AM »

Steve - I seriously doubt that ANY noise canceller will help you at all, no matter how much it costs.  Maybe "one day" DSP will be able to differentiate between unwanted noise and the desired signal, but I do not think that day has arrived.

From the description of your conditions, I think you just live in a very bad location for receiving HF signals.  The inside antenna only makes things worse.

Sometimes there is just not a good answer to a problem, and I think this is one of those times.

Sorry.......

Dick  AD4U

This is my position as well. There is no silver bullet here. Some rigs do handle noise better than others and if you have any local ham friends you should maybe try a different rig at your location. Your antenna and its location is a BIG part of problem here. For starters turn off/disable preamp in rig. It is of no value to you here as it amplifies noise too. Also trying using attenuator at times to further reduce noise level. Granted, this will reduce received signal level as well but noise too and you will have to work stronger signals. You should also consider deploying a outside antenna wire at night sometimes that disappears before morning.
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AD0AE
Member

Posts: 79




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« Reply #6 on: January 23, 2013, 11:45:03 AM »

Hi all-

Thank you all for the responses so far!  I appreciate hearing about this.  When I put the dipole outside of my apartment (to a near-by fence - thin wire invisible type), I was hoping to have a reduction in noise.  The fact of the matter was that it was about the same!  That was disappointing.  And since it is winter I have abandoned the idea for the time being.

I also understand that filtering will merely reduce the bandwidth of the received signal.  And I understand how the mfj 1025/1026 works, in terms of phasing and gaining your noise to reduce it.   

I am hesitant to spend a bunch of money on something which may marginally improve things, at best.  I was more posting to get some feedback about "if this was your situation what would you do?"  I am just trying to brain storm some ideas.

All that being said, JT65 has worked well out of my apartment.  I can say I have racked up around 60-70 QSOs across the country using an indoor loop antenna.  Nothing DX, I have worked coast-to-coast.  I also don't have a ton of time these days anyway, and maybe get 2-3 hours on the weekend if  I am lucky.

I will say one last thing, besides JT65, I can hear CW really well in my apartment.  All the more reason to continue learning it!

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W4OP
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Posts: 441


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« Reply #7 on: January 23, 2013, 12:07:52 PM »

Just a couple of thoughts. From a wavelength standpoint, even though your antenna was outside it still was likely very close to the noise sources. Secondly, unless you had  effective  eliminated common mode on your feedline (an appropriate choke/balun) your antenna was effectively not outside as the outer shield on your coax was then also part of the antenna and  a portion of it is inside the house..

GL- tough situation,

Dale W4OP
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NK7Z
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« Reply #8 on: January 23, 2013, 06:06:44 PM »

Hi,

As WB6BYU said, it depends on the source type...  If the source is specular in nature, (i.e. a point source like an antenna, or object), and not distributed like power lines the RF Noise canceler works VERY WELL...  This assumes you have a decent noise antenna as well...

If you use it on distributed RFI, you will see almost no result.  I have an MFJ-1025 for sale on E-Bay now for that reason...  When I initially got it, my RFI was point in nature, now I have RFI that is distributed in nature.  It worked very well initially, after the RFI changed types it sort of worked... 

It sounds like for you, a filter might be better, but be aware that in some cases the filter cuts the receiver off...  Running JT-65 here, if I have a weak signal, I can copy it better with the filter off...  You might get one of the 1025's and try it.  If it does not work, resell it and try a filter...  I almost never use my noise filters when running digital modes, and almost always use them for voice...  Hope this helps...

73's
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Thanks,
Dave
For reviews and setups see: http://www.nk7z.net
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