Amazing Results With QRM Eliminator

[ghost123uk]

Ferrite beads / rings can often be used to good advantage on noisy wires

[johnkyrle]

Confused here.I suffer with major QRM issues as I have detailed here before.BUT,you need another antenna to attract the QRM I take it?You mention it needs to be tuned to,obviously,a different band.How is this achieved?Surely if QRM is present all across 11 meters then how can it be possible to draw that away from the main antenna?
So the QRM we are experiencing is really a second or third harmonic of 11 metres?If that is the case,I would not want to be operating on anywhere near 40-20 metres at the time.
Please explain

I'm no expert. But yeah you need an aux (noise antenna) to receive the QRM, Theory is the QRM received by the aux antenna and the QRM received by the main antenna will be out of phase with each other and will be cancelled out. And yeah its probably a harmonic of some other frequency, I get it all across HF.

If you use a noise antenna thats resonant on the band you want to work then theres a good chance it also will receive the wanted signal and cancel it, If the noise is local as in from a neighbours house then any random piece of wire should pick it up. In my case i know exactly where the noise is coming from and i'm able to place a noise antenna about ten feet from it,
Rough diagram of how it works

If you know what is generating the noise could it not be possible to go round to the house with a very large hammer???Joking,of course.I see how it works but still think it will somehow cause interference on the T.X side of things and that is something that,unless you are running more than the set limits (never) it will still cause issues.Bet it is a Sky Q box

[Classic]

My pc causes 5+ of noise and i've tried tiny bit of wire right next to it and still can't null it out.

Probably the two Dollar Chinese power brick

No you're wrong and that has nothing to do with this thread.

[Admiral]

My pc causes 5+ of noise and i've tried tiny bit of wire right next to it and still can't null it out.

Probably the two Dollar Chinese power brick

No you're wrong and that has nothing to do with this thread.

Pardon? QRM has a lot to do with this thread, are you on your period?

[Classic]

Probably the two Dollar Chinese power brick

No you're wrong and that has nothing to do with this thread.

Pardon? QRM has a lot to do with this thread, are you on your period?

Mate i didn't ask what was causing my noise. This thread is about how QRM Eliminators work,not what causes the noise in the first place.

I know you trying to be funny but nice try anyway

[Buick Mackane]

This might be worth a punt to anyone who's interested

http://www.ebay.co.uk/itm/SEM-QRM-Elimi ... 2848322492

[robber57]

Just for info, there something similar from mfj which has quite enough reviews in the ham world, most, if not all positiv :


There are some vids on youtube showing its performance and working, there is also a few mods for it to make it more suitable ( less deaf) for the very low frequencys, if i remember correct something like < 150 khz , a mod to eliminate the possible blowup from TX and/or burning the fuse/lightbulb and some more mods doing similar stuff.
I have one (second hand) but cant tell you how good it is, or not, as it is modified which makes it apperently deaf on 11 m, i have to reverse the mod but have not got the time to do it sofar.
Documentation is excellent with enough explanation and schematic going from the youtube vids i would say it is probably worth every penny but ofcourse that mostly depends on how far you wanna go with this fun hobby

[Admiral]

I had a 1025 that I recall looked the same as that, not too sure what the difference is, the results of a lot of faffing and twiddling where pretty unremarkable for me.

[robber57]

The 1025 does not have the telescopic mini antenna/socket.

The mfj manual does an excellent job in explaining how these devices work, from what i remember from reading the manual and or perhaps some other sites:
The noise antenna needs to be preferable on the same frequency as the reciever, if it does not listen to the band your receiver is on the device can never extract the noise from what you are listening on as it will have nothing to extract.
For 11 meter youre best of with a mobile whip roughly tuned, the tuning is not all that critical.

The device does not only work by faseshift, thats just the gearbox subtracting both signals by faseshift, its what is send to the faseshifter which makes the difference :the signal level difference which should be there for the box to able to work.

different sized and "focused" antennas but tuned to the same band will deliver two signals with the same spectrum but the larger antenna will have relativly more dx signals and less LOCAL noise while the small antenna, preferably as close to the noise source as possible, will have a relativly low amount of dx and a high amount of LOCAL noise, if you null-level the signals out the difference in noise levels will make that you end up with less noise because you deduct a lot of noise and little dx from a source that has a lot of dx and little noise
I used the word "focus" to describe the lenght/height/design combination and the effect it has on a antenna for its preference to receive dx or local.
So you want the main antenna to be as much "dx" as possible and the small antenna as "local" as possible.
If the noise source comes from further away it may become benificial to move the small antenna more towards the main antenna to get enough sensitivity for it to detect the noise.

This also means that there are scenarios wheres it will not work or little, the furter away youre noise is coming from the more difficult it will be to achieve different level-profiles on the two antennas and so the less difference to deduct and so the box will appear to do nothing.

[Admiral]

The 1025 does not have the telescopic mini antenna/socket.

That probably sounds about right, I'm in a hotel room at the moment and the wifi is tragic so can't load pictures, only text, not too sure what use a telescopic whip would actually be unless the QRM was coming from the same room as the radio was in. Anyway, I wouldn't recommend the MFJ1025 to anyone to 'cure' their QRM/PLT, it did make a slight difference, but nothing to write home about.

[Buick Mackane]

How they can justify £200 plus for the MFJ is beyond me. It has auto tx sensing which they advise against using, Well whats the bloody point in having it then?

[robber57]

There is indeed not so much to say for it besides the following; the x-phase appears to be a design originating from a german ham, the original design had some flows and various partys have adopted and or changed the design and sell it.
The wimo version has a sensing option like the mfj so you can use it without the control connexion, on both it is advised not to use it as it can fail and the box will burn up( the mfj has a sort of fuse/lightbulb), the other versions can have cheap relays which sometimes fail.
I cannot find the original specs and i am wondering about the bandwith, i already spotted versions for lf-mf and mf-hf just like improvements for the "blow-up" possibility which greatly depends on the relays, the mfj appears to have decent relays, the circuitry looks decent quality and it has a switch for lf-hf and a switchable pre-amp making it more suitable to a wider range of antenna levels, i have no idea if that all adds up to better performance but it seems plausible.

The problem with all these devices; "your milleage may vary" , the all do work but how well depends on lots of variables, they all seem to work well with close by noise from devices like plasma tvs and the mfj does that with the telescopic antenna as long as it it is roughly in the neighbourhood of the tv which maybe a handy option, it has a even more sensitive pre-amp which needs to be activated by jumpers
With plt noise i have seen youtube clips from mfj,wimo and x-phase showing varying results.
It helps a a lot to determine what and how to use for the sense antenna if you know what your noise source is, and thats not always clear.

[Buick Mackane]

The wimo version has a sensing option like the mfj so you can use it without the control connexion,

Thats news to me. Unless theres a new version of the wimo, The wimo is overpriced too at around £160. It doesn't even have a metal enclosure. The one i'm using is called an xphase and as far as i know uses the same circuit as the wimo but at a fraction of the price. Bandwidth is apparently 0 - 30 mhz. i've used it on 11 metres & 40. it tunes over roughly 100khz before readjustment of the controls is needed

[robber57]

, i may have a screwed up memory and the wimo is the one with the exploding relays, there is another x-phase version with sensing option but apperently i have mixed these up in my head, i have read A LOT about this misery as i am also a victim of whatever the heck is screwing up my recieve, but in my case its only on 11 meter as i have recently discovered when i used the fft of my scope in combo with a active miniwhip antenna, it nicely showed me some horrible noise generator which pulsating spews out crap all over the 1-50 mhz range but clearly notch filtered on all ham,broadcast and official wavelengths but not on 11 meter , its filtered on 10 and 12 but not on 11m
I now concluded it must be a plt which is notched but not on 11 m.

The x-phase design got some bad wrap on several ham forums i read and the mfj was repeatedly suggested as a better solution with flatter frequency respons and a manufacter designed mod to greatly improve the receive on vlf (which the x-phase should not cover?)so i bought one second hand as the price is indeed steep, i discovered to late that it is modified to vlf but as i recently discovered what the source of my trouble is i am getting anxious to fix the mfj.

Using the fft on a scope is btw an interesting way of looking at the noise problem, if anyone is interested i can try to get some screenshots or perhaps a small vid of how this looks in spectrum, i was quite surprised to be able to actually see individual ham and cw stations in the spectrum as i also recieved them on my shortwave receiver, a bit like a pan adapter but different

Some interesting links: http://www.haje.nl/index.php?cPath=30_2280
The original design by DK9NL : http://www.darc.de/fileadmin/_migrated/ ... ltplan.pdf

[johnkyrle]

So is there a way to connect the noise antenna to the set directly?Or do you need the eliminator for it to run through?Sorry for appearing thick.I did my radio licence back in 1983 so am a bit rusty