DSP Filter or Noise cancel (MFJ)

[gcopter1]

I'm looking at MFJ models 784B(Tunable DSP Audio Filter) and the 1026(Deluxe Noise Cancel, Enhancer,Antenna).

They look very similar to me in what they do.

I would want to use one for SW listening, don't need it for transmitting.

Not too sure about what to get.

I'm using an Alinco DX-R8.

Thanks.

 

[WA8ZTZ]

They are actually quite different in what they do.

The 1026 can be set up to null undesired signals and noise as well as peaking desired signals.
It is installed between the antenna and the receiver. It takes some finesse to tune it properly
but can be very effective.

The 784B processes the audio and is installed between the receiver audio output and the speaker or
headphones.

Have limited experience with the 784B but have used the MFJ 722B Optimizer and the MFJ 1026 with
the Alinco with good results.

What is your specific situation ? What type of noise are you trying to eliminate ?

 

[gcopter1]

Apartment dweller, top floor, W6LVP loop in the balcony. Radio is on my desk along with noise producing devices.

 

[WA8ZTZ]

You have a challenging situation living in an apartment building loaded with the noise producing devices
of many occupants. The loop antenna is a good choice in such an environment.

You have no control over the noisy devices of the other building occupants but you can control what is in your own
apartment. Go around your rooms with a AM radio tuned to an open frequency and use it as a direction
finder to sniff out noisy appliances, etc. and install appropriate filtering or turn them off.

The 1026, in my experience, is good at eliminating a point source type noise but it seems to be less effective at trying to simultaneously
cancel out noise from multiple sources from multiple directions. Placement of the "noise" antenna seems to affect how well the 1026
cancels out noise... YMMV.

 

[majoco]

I made one similar to the MFJ 1026 a couple of years ago to try to null out interference from what I thought was a neighbours plasma TV. By the time I got it de-snagged and a temporary noise antenna erected, the noise stopped! Murphy strikes again. It did work quite well, either for reducing an interference source or enhancing a wanted signal - but was it worth the effort? I don't think so. A major improvement I made was to erect a large triangular loop with a matching transformer - I guess the lower impedance of the loop reduced the electrical noise pickup.

 

[gcopter1]

Ok so, since I last posted, I've been giving this some thought.
Bear in mind, I've only have had the radio less than month and my time listening, is only at most 2-3 hours every night. IMO, not enough time to evaluate what I think is man made noise.

The noise isn't so bad after all, at least by from what I've seen on YouTube. I have a battery charger on my desk that just today, even while not charging anything, made some of the noise. I unplugged it and most of the noise went away.

The rest, I think, is atmospheric in nature.

For now, I'm leaning towards the DSP.

I live in central Florida and at night, I DX the AM band for a station in Miami, about 195 miles south of me.
The station is on 670kHz but, is blanketed by a radio station in Cuba!

Rotating the loop and fiddling with the knobs on the Alinco, I can get a bit louder audio from Miami but, I believe if I had the DSP, I would be able to completely bypass the cuban signal and let the one Miami come thru better.

FWIW, I'm using the NB and the Narrow mode on the Alinco most of the time.

 

[ka3jjz]

While the DSP might make the audio a bit cleaner, it will not have any other effect on the signal. The ultimate problem is that the Cuban is probably getting to your radio at a nearly identical path that the Miami station is using. The loop can only do so much in such cases. You MIGHT have better luck if you could get the loop outside away from the home, but that's a big if.

A very good way to visualize this is to take 2 flashlights, and make one shine on nearly the same path as the other. Just off maybe an inch or two.

Mike

 

[WA8ZTZ]

If the Miami station you refer to is WWFE AM 670, be aware that at night that station only runs 1kw and the
nighttime pattern directs most of the signal to the east (perhaps to protect WSCR Chicago on the same frequency).
OTOH, some quick internet research shows 670 to be a popular frequency in Cuba with a number of stations running 10kw.

As Mike mentioned in the post above, the Miami station and Cuban station(s) are pretty much straight away from you
on a nearly identical path. Your loop is going to have a tough time trying to separate the signals.

 

[gcopter1]

Yep, that's the one. No wonder the Cubans are blanketing the station in Miami.

 

[WA8ZTZ]

If you are into AM broadcast band DXing, you will find that the MFJ 722B Optimizer audio filter will work well
with your Alinco. It will greatly cut down on the hetrodynes and warble. It will not, however, filter out one
station in favor of another on the exact same frequency.

Another couple of techniques... try tuning off the center frequency a kc or two either way, it will sometimes
clear up the signal a bit. Also, try tuning in the AM signal using LSB or USB mode, it will make the audio sound filtered but
will also cut down some of the interference. Use the RIT as a fine tuning control.

 

[majoco]

What WA8ZTZ said. The most I can offer is - learn all about your receiver and how to get the best out of it. It's impossible to separate two transmissions on one frequency no matter how many bells and whistles you have (unless they are different bearings from you so a directional antenna may separate them) but you can often get rid of an adjacent signal by choosing a narrower filter, using USB or LSB so that you can move the offending station out of the passband, using the RIT control and filters together. Above all, practise, practise and practise! The more familiar you are with what the knobs do, the more you will get out of it. Learn all about propagation too, you may find listening at another time of day or night will produce better results.

 

[ka3jjz]

Martin's trick - which is often referred to as Exalted Carrier Single Sideband (ECSS), or less commonly, Zero Beat Tuning - works well when the interfering station is a khz or two away. Don't forget to try your IF Shift to see if that helps. When using ECSS, precision tuning is a must. Use the smallest tuning step you can.

The Cuban might be just slightly off frequency - it wouldn't be out of the question - and if it is, you might have a shot at separating the two. But if they're both precisely on the same frequency, as Martin correctly points out, there's little you can do about it, particularly since the path of both stations reaching you is very nearly the same

Mike

 

[Scan125]

For what it may be worth:

I have no loop experience and use my DX-R8 on a coax fed external long wire (10m+). On its own I had good results with a balun. I later removed the balun and installed MFJ-956 Antenna Tuner. With this I was able to get much better signal to noise ratio. "On" frequency signal strength was increased and off frequency noise reduced.

I've since upgraded to an MFJ-959C. The suits my requirements even better as it has built in Attenuator, Signal Amp (variable gain), and will handle two receivers and two antennas. Also tunes both antenna side and tuner side.

As you have the DX-R8 if you have not already seen my free DriveR8 Control Program and have a PC then you may want to check the program out. It includes scheduled tuning and audio recording functions so you can let your DX-R8 tune an listen while you are out or asleep.

Link is in my signature below.