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eHam Forums => RFI / EMI => Topic started by: VE3TMT on March 15, 2013, 05:46:32 AM



Title: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 15, 2013, 05:46:32 AM
Go the unit hooked up last night, unit is set up through the RX ANT loop on the FT-990. Currently I am using what amounts to a longwire antenna (the center conductor only of an used run of coax that goes up the tower) for the sensing antenna and the sloper as the main antenna. Interference problem is mainly on 160 and 80. Adjusting the noise antenna gain does increase or reduce the noise, while adjusting the main gain does the same on the signal. I have tried all different settings, followed the instructions to a "T" and cannot get the noise down more than a couple of db, say from 20 over down to about an S9. There is no deep null as was expected.

If I listen to the offending signal on the regular antenna, it is a very pronounced buzz, very easy sound to distinguish. When I turn up the noise antenna gain, the interference does not sound the same, it's more like hashing or a wider type of noise, so I'm not sure if maybe the problem isn't with the "noise" antenna. Just to test, I reversed the antennas, used the sloper as the noise antenna and the longwire as the receiving antenna. Still the same results.

So before I go stringing up another antenna, am I doing something wrong? I also hooked the unit up direct, antenna to unit, unit to antenna connector on the radio (not through the RX loop) and had the same results.

Any suggestions?

Max


Title: RE: MFJ-1026 What am I doing wrong?
Post by: WB4BYQ on March 15, 2013, 07:00:23 AM
Your norm tx/rx ant and the noise rx ant have to hear the noise and the noise ant needs to have a good level of signal from the noise to adjust the gain and phase to cancel the noise.  i would
hook the unit up with the normal connections with the tx/rx and noise rx to the 1026.  first listen to the noise thru the 1026 with the tx/rx ant, then remove the tx/rx and replace it with the rx ant
and see if you hear the same signal.  the way the rx hears the signal will affect the phase and gain of the 1026.  i have use both with good success to cancel rfi.

Time and practice the help.

richard


Title: RE: MFJ-1026 What am I doing wrong?
Post by: AJ8MH on March 15, 2013, 07:04:55 AM
Just to test, I reversed the antennas, used the slopper as the noise antenna and the longwire as the receiving antenna. Still the same results.

When you swapped antenna inputs, did the buzz being picked up your regular antenna still sound like a buzz.  Just want to make sure your sense input port is working properly.

I have one of these units and it works great, but both ports must hear the same "noise."  (The noise sounds the same.)  Make sure the shorting clip on the circuit board is in JMP 1 position.  Make sure the FREQ selection button is out for 80 and 160.  Turn the pre-amp on.  Phase at zero.

I adjust mine a little differently.  First, I bring up my aux gain so the noise is heard.  I try for about an S-3 to 5.  Next, I bring up the main antenna gain until I see the S meter increase slightly.  Next, I adjust the phase for a nul.  It seems to work best when the phase ends up between 8 and 9.  Try the phase normal/invert switch.

My settings are currently set at 5 (AUX Antenna), 8.5 (Phase), 2.5 (Main Antenna) and normal (Phase).  Yours may be different.  I never use the rig's rx pre-amps on 80 and 160.



Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 15, 2013, 07:36:29 AM
The more I think about it, the more I think the issue is with the sensing antenna. I don't think using the center conductor of a length of coax will cut it. Problem is I can't get up the tower to hook it to anything. I am going to try my scanner antenna (it's a vertical) to see how well that hears the noise, but need to run that coax into the new shack before I can try it.

I would ideally like to run a wire parallel to the sloper, but not sure I can do that. I can run a longwire (a real one) from the chimney over to a tree and down to the pole where the end of the sloper is attached. This will at least get the sensing antenna over to where I think the noise is coming from.

As a test, I put the rig on 1.955, where the interference is the worst, and switch between the sloper and beam. They both hear the interference differently. On the sloper it is just a loud 20 over 9 buzz. On the beam its about S7 but does not have the same buzz characteristic. I think this is what the current sensing antenna is hearing.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: PA3GOS on March 16, 2013, 03:30:04 AM
The goal for the aux. antenna would be to receive as much of the same noise as possible but to receive as little "wanted" signals as possible.
So, running a wire parallel to your sloper does not sound like a good idea. You will, most likely, null the noise but also most stations you want to hear.

I am currently using my 1025 (not 1026 but the idea is the same) to null a local noise source on all bands. Like you, I am using a random wire (25 meters) to pick up the noise. Unfortunately, it will only pick it up on 40 and 80. Not sure about 160 since I have no antenna for it.

Currently I am thinking about an active antenna. Preferably a small loop due to it's ability to aim to the noise and, hence, pick up less stations.

The unit works very well but it does need a good "noise antenna". Someone else's settings may never be yours. It's highly dependent of the phases and strengths in your particular situation. 


Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 16, 2013, 02:54:04 PM
Spent the day trying different noise antennas, run a wire parallel to the sloper, across the yard, around the roof, in none of the configurations is the noise antenna hearing the same signal the sloper is. So needless to say I am not getting the results I was expecting. May be time to give up 160 and 80.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: AJ8MH on March 16, 2013, 03:49:00 PM
Interesting. What does a CW signal sound like when you switch from the sense antenna to the main antenna and back? Alternately turn the gain of the antennas down with the 1026 to compare.  And, turn your FT-990 receiver pre-amps off, if you can.

On mine, there is a little difference in S meter readings, but signal sounds the same.  I'm trying to understand why the noise (buzz) sounds different, especially when your antennas were parallel.

Where do you think the noise is coming from?






Title: RE: MFJ-1026 What am I doing wrong?
Post by: WB4BYQ on March 17, 2013, 06:51:14 AM
Maybe the tower is picking up the noise.  was tracing some noise the other day at
another hams home and the tower was hearing another noise other than the one we
were trying to find.  Tower equal vertical ant.


richard


Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 18, 2013, 06:27:49 AM
Interesting. What does a CW signal sound like when you switch from the sense antenna to the main antenna and back? Alternately turn the gain of the antennas down with the 1026 to compare.  And, turn your FT-990 receiver pre-amps off, if you can.

I'll try this tonight, I don't think the 990 has a preamp, but I have also tried it with the RF ATT on.


On mine, there is a little difference in S meter readings, but signal sounds the same.  I'm trying to understand why the noise (buzz) sounds different, especially when your antennas were parallel.

Not sure, but all antenna combinations were tried and I can't get the same noise on the sensing antenna. I also noticed the internet/phone modem is causing noise, I will be calling the cable company to see if they are aware of this.

Where do you think the noise is coming from?
 
I am suspecting a neighborhood Plasma TV or some other power supply. At first I thought it was an arching streetlight or transformer, but I have walked or driven up every road within a kilometer distance from my QTH with a portable receiver and was not able to find the noise. Also used the car AM radio and no luck. So I think it is very close to the house, that is why I suspect a TV or power supply from some other electronics.


Yesterday and this morning I noticed more noise on the band. As far up as 15m, an S5 noise across the whole HF spectrum. May be time to pack in HF and move up to VHF/UHF operations! Or get a new hobby.








Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 18, 2013, 10:44:37 AM
Maybe the tower is picking up the noise. 

The 160/80/40 antenna is an Alpha Delta DX-B sloper, which uses the tower as a counterpoise. You may be correct. I do see a slight null, but only about 2 S-units. If I really want to knock the noise down, I can turn down the gain of both antennas, but then I'm not hearing anything.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: K5TED on March 18, 2013, 06:56:52 PM
Find a portable AM radio. Not a portable HF receiver. Just a good old transistor radio wih the ferrite bar antenna. Find the noise. Use a map of your property to triangulate.

If the noise seems to be coming from all directions, pick a day when no one is home, and start by turning off breakers in your house panel, one at a time. See if the noise stops.

If the noise continues, try using the coax shield instead of the center conductor as the sense antenna, since the noise is obviously local in nature. Very local. Maybe a switching power supply. Maybe the one you are using to power the radio. Try a different power supply.




Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 18, 2013, 07:07:46 PM
Find a portable AM radio. Not a portable HF receiver. Just a good old transistor radio wih the ferrite bar antenna. Find the noise. Use a map of your property to triangulate.

If the noise seems to be coming from all directions, pick a day when no one is home, and start by turning off breakers in your house panel, one at a time. See if the noise stops.

Tried that, with all breakers off, noise is still present.

If the noise continues, try using the coax shield instead of the center conductor as the sense antenna, since the noise is obviously local in nature. Very local. Maybe a switching power supply. Maybe the one you are using to power the radio. Try a different power supply.

Done that as well. It's not the radio, had the same problem with my TS940.


I used a splitter and hooked my sloper to bot the radio and the 1026. Was able to null the noise from 20 over to S-0 so I know the MFJ unit is working. Just need to get the sensing antenna to hear the same noise the sloper does.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: K5TED on March 18, 2013, 07:44:21 PM
Sounds like you're on track. I wore my fingers out tweaking the 1026. Sometimes it works wonders, sometimes it seems to do nothing at all. One example of working wonders is that it could almost completely kill the jamming of Radio Marti. One example of doing nothing is trying to null out local noise.

It's in a box, in the closet.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 19, 2013, 06:45:59 PM
I have tried everything, running the noise antenna parallel to the sloper, ran it perpendicular, regardless of the configuration I cannot get it to hear the same noise as the sloper. I really don't know what to try next.

The sloper is at about 30' of the side of the tower sloping east, and about 10' off the ground at the far end. The noise antenna is about 60' of 12 gauge wire connected to the center of an unused piece of coax. There is no ground connection on this antenna. Could this be part of the problem?


Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 20, 2013, 06:39:54 AM
I ran the sensing antenna from the chimney over to the tree and down to the same end support as the sloper, so the "noise" antenna has both a parallel and perpendicular element to it. Is still does not pick up the loud "buzz" the sloper hears. I am totally at a loss. I have tried every configuration possible and I cannot duplicate the interference on any RX/TX antenna. Even my 3 element HF beam does not hear it the same way.

I think I am going to have to remove the sloper and just run a long wire for my low band antenna, probably won't perform any worse than the sloper and at least this way I won't hear the interference.

Is it possible the sloper is picking it up differently because of it's configuration? As mentioned, the tower is the ground half of the sloper and it runs easterly at about 30' at the top and 10' at the bottom. It is a DX-B.

My last effort may be to just run two parallel wires from the tower down to the lower support and separate them by a few inches. Feed them with separate coax and use one for the RX/TX antenna and the other for the noise antenna.

Can't really think of any other options.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: PA3GOS on March 20, 2013, 08:01:00 AM
It sure is strange that none of the configurations you tried so far picks up the noise the way the sloper does.

I am also trying different things myself. My 25 meters long extensioncord works just fine on 40 and below. Until today it was directly connected to the 1025.
Yesterday I stopped by the local hamshop to pick up some 15 meters of Aircell 5 coax. Soldered a PL-259 on one end and tried several things to pick up the noise  loud enough on the higher bands. Like using the gutter, the tower etc.
Haven't succeeded so far.. Last thing I did was connect the center of the coax to the extensioncord. Still no luck but it works on 40 and below as before.
Only the "Phase" settings have changed of course.
Guess I have to try a shorter wire and get it up higher to pick up the noise well enough on 20 and above.

If you are going to run a sense antenna in close proximity of your main antenna you might, as I did, want to modify the sense antenna input on the unit.
An extra relay (in my case with the coil simply parallel to the existing one) pulls the sense antenna input to ground while transmitting or switched off.
This also enables you to remove the lightbulb and gain an extra 2 dB in sensitivity for the sense antenna. 

I'll try to keep you informed when I make progress.

73, Tjalling PA3GOS


Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 20, 2013, 08:30:32 AM
If you are going to run a sense antenna in close proximity of your main antenna you might, as I did, want to modify the sense antenna input on the unit.
An extra relay (in my case with the coil simply parallel to the existing one) pulls the sense antenna input to ground while transmitting or switched off.

Can you email me more information on this modification? Please email me at
mycallsign at yahoo dot ca  (ve3tmt @ yahoo .ca) no spaces

I am going to do the W8JI mods as well as I do not plan on transmitting thru the unit. I use the RX antenna loop on the FT990.

Thanks,
Max


Title: RE: MFJ-1026 What am I doing wrong?
Post by: W1VT on March 20, 2013, 10:25:58 AM
You will not be able to get a deep null if there is more than one noise source.

If there are two noise sources, in theory, one could use two null cancelers, one for each noise source, to eliminate both noise sources.

Zack Lau W1VT


Title: RE: MFJ-1026 What am I doing wrong?
Post by: VE3TMT on March 20, 2013, 10:31:24 AM
If it ever came to that I think I would just give up operating on 160 and 80. I don't really do much there now, more listening, but hard to listen with a 20 over buzz. I do have to give the 990 credit, between the notch filter and the IF shift, it does a fair job. The NB is pretty ineffective on the buzz, my old TS940's did a much better job.


Title: RE: MFJ-1026 What am I doing wrong?
Post by: W1VT on March 20, 2013, 12:07:17 PM
http://vk1od.net/measurement/noise/FSAmbientNoise.pdf

Here are some noise versus frequency plots that show noise levels from an ITU study plotted on a graph--together with "S Meter Readings"   to make the numbers more understandable to the average ham.

It is not reasonable to expect an "S6" noise level on 80 meters with a full size antenna--unless you actually move to a rural area! 

Zack Lau W1VT


Title: RE: MFJ-1026 What am I doing wrong?
Post by: PA3GOS on March 21, 2013, 01:51:43 PM
If you are going to run a sense antenna in close proximity of your main antenna you might, as I did, want to modify the sense antenna input on the unit.
An extra relay (in my case with the coil simply parallel to the existing one) pulls the sense antenna input to ground while transmitting or switched off.

Can you email me more information on this modification? Please email me at
mycallsign at yahoo dot ca  (ve3tmt @ yahoo .ca) no spaces

I am going to do the W8JI mods as well as I do not plan on transmitting thru the unit. I use the RX antenna loop on the FT990.

Thanks,
Max

Hi Max,

Check your email. Took me a bit of time to do it but hope it is clear.
And, if you are going to use the RX antenna loop of your radio, please do connect the "control" RCA on the 1026 to the radio.
If you can't for some reason, transmit through it. This is because the extra relay has to switch to "not engaged" in order to protect the AUX input.

73, Tjalling PA3GOS