I Bought The CMC 130-3K....

ridgescan

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Apr 1, 2008
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San Francisco, Ca.
....from MyAntennas. I put it in line near the receiver. No difference in any noise floor between signals across the HF bands. I think there's a notable improvement with the white noise that occurs during carrier fades with SW broadcasts, and I think I see some cleaner MW signals like when I'm listening to my favorite daytime Sacramento MW station from here in San Francisco.
My question: would this thing help more with noise if I put it up near the antenna feed point on the roof?
Or should I buy a second one and run 'em at both ends of the feed line?
 

markclark

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I read different opinions about placement. I've tried installing the choke at both the antenna and at the radio, and, chokes at both ends of the coax at the same time. I can't tell any difference in noise levels with any of the above arrangements. I use the My Antenna line of common mode chokes, they are well made and have very good specs. The only thing that lowered my noise floor in the city was an active loop and a powerline conditioner. I moved to the country and my noise floor is now about 1 db or less.

The choke not having much effect suggests that your noise is not common mode noise. And, living in an apartment you are surely experiencing noise from neighbors routers, dishwashers (yes dishwashers), grow lights (the worst offenders of all), plasma TV's, solar panel power inverters - you name it. A high quality powerline noise conditioner is a must in your situation as well. A decent book for low cost is the ARRL RFI noise book to help solve many RFI noise problems. Good luck.
 

ridgescan

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I read different opinions about placement. I've tried installing the choke at both the antenna and at the radio, and, chokes at both ends of the coax at the same time. I can't tell any difference in noise levels with any of the above arrangements. I use the My Antenna line of common mode chokes, they are well made and have very good specs. The only thing that lowered my noise floor in the city was an active loop and a powerline conditioner. I moved to the country and my noise floor is now about 1 db or less.

The choke not having much effect suggests that your noise is not common mode noise. And, living in an apartment you are surely experiencing noise from neighbors routers, dishwashers (yes dishwashers), grow lights (the worst offenders of all), plasma TV's, solar panel power inverters - you name it. A high quality powerline noise conditioner is a must in your situation as well. A decent book for low cost is the ARRL RFI noise book to help solve many RFI noise problems. Good luck.
Thanks Mark. You're lucky having that low a noise floor-you must really enjoy that. I hit up Danny at MyAntennas and said pretty much the same as what you said. I have the CMC on the endfed wire now-I'm gonna try it on the Wellbrook next.
 

ridgescan

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I got 2 of them and tried different combinations with no sucess...

Regards Lino...
Hey Lino long time no see! Yeah when I emailed Danny who I think is the creator of these things, he seemed to resign to the same thing. I even asked him if a second one at the feed point would help and he basically said "don't bother".
$100 down the hole I guess.
I hesitated buying it at first after reading all this hype last year about how well it works, but finally caved and got one anyway last week. I guess it only works well in certain ideal situations, and not at all or barely in others:(
 

prcguy

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I probably recommended the MyAntennas CMC but I also remember mentioning its a good idea to borrow or steal one for testing before buying due to everyone's different setup. I have several here I would be happy to loan to locals, or I would have been happy to ship one to ridgescan to see how it works out.

In my case I was running a ZS6BKW HF antenna that needs a common mode choke and the coax/ladder line junction and I had a home made one with maybe 8 turns of parallel wires around #31 mix core. I swapped that out with a MyAntennas choke and immediately noticed the noise floor on my spectrum monitor went down a few dB and some birdies and fuzzy noise lumps were reduced. I was so happy I put a second one at the radio end where the coax exits the house and after it passes by all my computer cables and that improved things further, although not as much as the first one at the antenna.

So I have a specific problem here of RFI being induced onto my coax shield and traveling up to the antenna and the CNCs did a great job here. If you don't have RFI riding on the coax then a CMC may not make a dent in your noise floor but it definitely isolate the antenna from the feedline by 30-40dB and that is a good thing.

I also have a camera security system with shielded CAT6 running all over the roof and that system creates a lot of noise bumps and interference in the HF range. I've treated all the cameras with winding 4 to 6 turns of CAT6 through a very large snap on 31 mix bead and that really calmed things down but I still have noise here and there from some cameras. A CMC in my feedline has no effect on that noise because its radiated from the camera and the CAT6 cable as an antenna. My final fix for that was installing an Internet controlled AC switch on the camera system DVR, which powers the cameras and I turn them off if I'm operating right on a noise bump.

The remote control switch is nice because I use some of my radios remote while traveling and I can turn the camera system off remote from across the country while operating remote from across the country. There is usually a fix for everything even though it might not be ideal.

Here are a few spare CMCs I have and there are probably 6 or so in use at this location and several more at my remote locations. I love these things. And the MyAntennas tubular versions work better than any other I've tested.

CMC.JPG

Hey Lino long time no see! Yeah when I emailed Danny who I think is the creator of these things, he seemed to resign to the same thing. I even asked him if a second one at the feed point would help and he basically said "don't bother".
$100 down the hole I guess.
I hesitated buying it at first after reading all this hype last year about how well it works, but finally caved and got one anyway last week. I guess it only works well in certain ideal situations, and not at all or barely in others:(
 

ridgescan

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Joined
Apr 1, 2008
Messages
4,710
Location
San Francisco, Ca.
I probably recommended the MyAntennas CMC but I also remember mentioning its a good idea to borrow or steal one for testing before buying due to everyone's different setup. I have several here I would be happy to loan to locals, or I would have been happy to ship one to ridgescan to see how it works out.

In my case I was running a ZS6BKW HF antenna that needs a common mode choke and the coax/ladder line junction and I had a home made one with maybe 8 turns of parallel wires around #31 mix core. I swapped that out with a MyAntennas choke and immediately noticed the noise floor on my spectrum monitor went down a few dB and some birdies and fuzzy noise lumps were reduced. I was so happy I put a second one at the radio end where the coax exits the house and after it passes by all my computer cables and that improved things further, although not as much as the first one at the antenna.

So I have a specific problem here of RFI being induced onto my coax shield and traveling up to the antenna and the CNCs did a great job here. If you don't have RFI riding on the coax then a CMC may not make a dent in your noise floor but it definitely isolate the antenna from the feedline by 30-40dB and that is a good thing.

I also have a camera security system with shielded CAT6 running all over the roof and that system creates a lot of noise bumps and interference in the HF range. I've treated all the cameras with winding 4 to 6 turns of CAT6 through a very large snap on 31 mix bead and that really calmed things down but I still have noise here and there from some cameras. A CMC in my feedline has no effect on that noise because its radiated from the camera and the CAT6 cable as an antenna. My final fix for that was installing an Internet controlled AC switch on the camera system DVR, which powers the cameras and I turn them off if I'm operating right on a noise bump.

The remote control switch is nice because I use some of my radios remote while traveling and I can turn the camera system off remote from across the country while operating remote from across the country. There is usually a fix for everything even though it might not be ideal.

Here are a few spare CMCs I have and there are probably 6 or so in use at this location and several more at my remote locations. I love these things. And the MyAntennas tubular versions work better than any other I've tested.

View attachment 89781
Naw I was with you on these chokes-it does seem to do something for MW and also for SW BCs white noise with carrier fades. And I'm sure it's doing stuff I haven't recognized yet..I've only had it for a few days.
It's just that out of the box, it didn't slap me in the face with any kind of noise floor reduction whatsoever.
I might try it on the Wellbrook loop when I get a chance and see if it shows anything there. It could be my wire antenna just sucks along with all the RFI in this place. The antenna does very well, don't get me wrong, but there exists these nasty noise gremlins to go with it.
I'm glad I bought it though prcguy, cause when I finally move to Rocklin/Roseville it may be effective there who knows:)
 

WA8ZTZ

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Feb 23, 2014
Messages
787
Have tried a couple of common mode chokes here (one commercial, one homemade) with limited success on strong local powerline noise.
Tried it directly at the radio with a double-ended PL-259 and up at the antenna... very little help. Leads me to believe that the noise was not common mode type. In other words, your noise may not being picked up by the coax lead-in. Common mode is only one of the many ways that noise can get into a radio. However, sometimes, you don't know unless you try something.
 
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