VK3TEX Noise Blanker Demo with MFJ1026 and ICOM 7610

V

VK3YNV

Guest

My 80 antenna is a trapped inverted V and the noise antenna is a 80 meter mobile stick stuck To the side of the pergola.

Ideally the noise antenna should be the size of the main antenna but that’s not possible at My QTH.

Posted for Les VK3TEX

Edit: Changed thread title from MFJ 1206 to MFJ 1026 -- Thanks Les
 
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V

VK3ZYZ

Guest
Looks pretty impressive.
That cleaned the signal up quite a bit.
 
V

VK3YNV

Guest
Looks like black magic.

I assume that it's only in the receive signal path, does it switch out automatically on transmit?

Edit: It appears to have a PTT line input as well as an RF sensing circuit to switch the noise canceller out on transmit.
 
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V

VK3YNV

Guest
For those like myself that are curious to see what a typical phasing noise canceller circuit look like... I found the following

Noise_Canceller.gif

Copied from here ... https://www.qsl.net/va3iul/Receiver_Noise_Canceller/Receiver_Noise_Canceller.htm

Looks pretty simple, just two pre-amps connected back to back with adjustable gain on both and adjustable phase on the noise antenna side.
I think I would have mirrored the input filtering on both sides, rather than just the main antenna side. Seems like low frequency noise would get through the noise antenna pre-amp and not the main pre-amp? Or am I reading that wrong?

I couldn't see what the extra relay (RLY2) was for, but now i get it, it's to ground the noise antenna when the main antenna is transmitting, so that high power from the main antenna doesn't fry the noise pre-amp.
 
sadarc

sadarc

Administrator
Staff member
A demonstration of the MFJ1026 with the ICOM IC780/1 during the ALARA contest. Watch the S meter jump up to S9 when the MFJ1026 is switched out.


Posted for Les VK3TEX
 
V

VK3TEX

Guest
Hi Guys,
I just sent Ray some more files this time of the ICOM 781 hooked up to the unit. I guess he will do his magic and post it here as well
or on another topic.
The unit does have RF switching inside and it works well and has a timing circuit you can vary for the receiver to come back after transmit is
finished. Mine is set to about 20ms and this works fine. You can see this transition happen on the band scope which is handy.

These circuits are not your average noise blanker or noise reduction. They work on an electrically steerable antenna concept(and pattern phasing). Nothing new about this, but its becoming more important with the increasing amount of rubbish noise on our HF bands....

The MFJ only has one pre amp for the noise antenna, while fairly low gain it is adequate, but only just.... i would have preferred double the gain
but my noise antenna is only very small, so more pre amp gain would have been better in my situation...
My next antenna related purchase will be a DX Engineering NCC-2 phasing unit(Google it!) similar to the the MFJ, but is a more Deluxe model and has a few additional features which are important to my experiments....

Cheers, Les VK3TEX.
 
sadarc

sadarc

Administrator
Staff member
Hi Les, I beat you to it by a few minutes. :)

I still think it's black magic. So I've been doing a bit of research on the topic, and the technique of separate noise cancelling antennas goes back to before WW2, and there has been a few write-ups in AR over the years, the one that Rod VK3UG pointed me to was a series of articles by Drew Diamond VK3XU that were published in AR back in the 1970's.

Interesting stuff.
 
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