RX Common Mode Filter Choke / Noise Suppressor / RF Isolator

[iMONITOR]

I use an ICOM IC-7600 transceiver for my SWL/amature radio monitoring rig. It's well designed and has abundance of features to attempt to provide good performance, NB, NR, Twin-PBT, Notch Filters, Roofing Filters etc. As I mentioned in another thread I recently added a Par BCST-HPF high pass AM broadcast filter. In addition I'm using an MFJ-1886 loop 'receiving' antenna (for low noise) with a built in preamp.

Now I've stumbled upon a RX Common Mode Filter Choke / Noise Suppressor / RF Isolator...phew that's a mouthful! I'm not wanting to spend more money on more gadgets just for bragging rights but I don't spending money anytime I can improve something. Considering I'm using this entire setup indoors, in my office without the advantages of an outdoor, big, high antenna, is this device something that will provide additional quality and clarity to my listening pleasure or is redundant and unnecessary? Things are working quite well without it, but I'm thinking this would help attenuate various electrical noise generated inside my home from just about everything.



This is the device I'm considering:
CMC-0510-R - MyAntennas.com

Please advise, and think you.

 

[cmdrwill]

Only covers Covers 0.5-10MHz. Look up Palomar Engineers I have very good results with their Common Mode Choke kit. And they cover the whole HF bands 2 to 50 MHz.
SLIP ON Sleeve Chokes - Palomar Engineers® SLIP ON Sleeve Chokes - Palomar Engineers®

 

[Ubbe]

Having the antenna indoors will let it pick up more interferencies than the coax ever can do, so a common mode choke filter will not do anything for you. You could try a noise canceller. It is a telescope antenna connected to your normal one and a box between that can alter the phase. Using the box you can adjust one source of interference to be phased 180 to the original antenna signal and cancel out the interference. It only works with one interference at a time but there's often a major one that helps a lot to get rid off. If the interference are travelling by the mains wiring it works as an antenna and comes from all directions and that's impossible to get rid off using a noise canceller. It's a box that changes the phase and adjusts the level to minimise the interference and all boxes should work the same. You can use different lenghts of coax to a second antenna to adjust the phase and then use a variable attenuator to balance out the interference, so it can be built by yourself or bought ready made at different costs.

Cancel Interference
Antenna phasing & noise cancelling- DX Engineering

/Ubbe

 

[prcguy]

I have several MyAntennas common mode chokes because they make a noticeable difference to me. They also have the most isolation or common mode rejection of any brand made at this time including Palomar.

The first time I used one was an experiment swapping out a home made 1:1 balun of about 10 turns of RG-142 coax around an FT-240-43 core at the coax to ladder line junction of a ZS6BKW dipole. Going from the home made to the MyAntennas CMC130-3K reduced my noise floor visibly on my Elecraft P3 spectrum display where many birdies and noise humps went away.

Turns out my coax passed through lots of computer cables inducing noise onto the shield of the coax and carrying it up to the antenna. My home made choke was helping but I had no idea the problem was real bad and that another type of choke would make such a big difference. Now I use them on everything at multiple locations including a CMC-0510-R on my new W6LPV receive loop. I chose the CMC-0510-R because I mostly use the loop for VLF through maybe 20m and it probably has more isolation at 14MHz out of its range than other brands do within their range. Otherwise the CMC-130-3K is the most effective commercially made choke for 160 through 10M on this planet, period.

You will never know how much it will help until you try one and in some cases there may be no improvement in noise. It would be nice if you could borrow one to test and then purchase only if you see an improvement. I have a couple of home made versions of the big MyAntennas CMC-230-5K choke using two FT-240-31 cores and two other types so each favors different parts of the band similar to MyAntennas, but I don't have his exact recipe. However it does work very well.

 

[prcguy]

Accidental duplicate post that was removed.

 

[iMONITOR]

Only covers Covers 0.5-10MHz.

Thanks for pointing that out. I found and ordered the CMC-130-3K 1-30MHz 1-30MHz instead.

 

[Ubbe]

I think you're paying mostly for the 3000watt capability and can build a low power filter for $6.
Read this informative document https://www.okdxf.eu/files/CoaxChokesPPT.pdf

/Ubbe

 

[prcguy]

For the tubular MyAntennas chokes your paying for a lot of ferrite and engineering. These are not simply beads over the coax, there are a bunch of very large beads of different permeability with varying numbers of turns around each one making a multi section choke. This is to give huge restive choking impedance over a very broad range of frequencies and much wider that you can achieve with a bunch of beads over coax or coax wound over the same mix cores.

There is probably $20 of ferrite in some of the tubular MyAntennas chokes and for their 5kW version there are four 2.4" cores at about $10 average per core.

I think you're paying mostly for the 3000watt capability and can build a low power filter for $6.
Read this informative document https://www.okdxf.eu/files/CoaxChokesPPT.pdf

/Ubbe

 

[nanZor]

I would have stuck with your original thought of the CMC-01510-R, which has better specs down to 0.5 mhz for a *receiving* application since that's where AM BCB lives and might be helpful in case you are being interfered with by a high powered AM station sneaking in through the common mode of your coax. I have one and really like it for RX purposes. Certainly any BCB dxer would probably prefer it

I hate to say it, but to me it seems like you are kind of throwing darts at the dartboard with products you may not really need in your situation.

The good news is that even if you don't actually have a demonstrated need for it, those parts will come in handy down the line for other things you may build in the future.

 

[WA8ZTZ]

You will never know how much it will help until you try one and in some cases there may be no improvement in noise.

this ^^^

 

[nanZor]

Wow - I just proved to myself that I needed TWO of the chokes, even *if you can't hear a problem* !!

How did I discover this? Like many swl / amateurs, I run a linear power supply and not a switching supply. So I thought things were under control with no growlers and other noise carriers walking around.

BUT, I was testing a switching supply for transmit purposes, and lo and behold on 160 and 80 meters, all the gremlins started walking around with my on-ground antennas that have a great s/n ratio, making it easier to hear a problem not being masked by noise.

Ok, fine - the best choke from myantennas for receiving the low bands CMC-0510-R is in use at the feedpoint. Still, some gremlins are making it back. Only *another* choke, this time the MFJ 915 placed near the receiver off a 3 foot jumper (never put them directly on the receiver jacks - use a small jumper) got the gremlins to nearly inaudible status.

If it wasn't for this test by purposely using a switching supply for transmit on 6 meters, and the great s/n ratio of the on-ground antenna, this problem would have been well hidden by band noise - meaning that my antenna pattern was being affected to some degree.

For nearly the same price as the 915, I'll be getting another CMC-0510-R for use near the rig as a replacement for the MFJ - even though that did work ok after the rig.

So that's going to become my standard - a choke in use near the feedpoint AND ANOTHER hanging off a small jumper near the rig. Just because you can't hear it, doesn't mean your antenna pattern is not being affected, or being unprotected from something else that may pop up later.

Yeah sure, I could use a notch filter, but I want to do it right. So TWO chokes are my minimum now, and I'll take back my statement about demonstrating an audible need for one.

 

[prcguy]

I also use two chokes on all my HF feedlines, at the antenna and at the radio. I discovered the need when I first started using radios with spectral displays. That will really show you how a choke balun can reduce noise. And all 1:1 choke baluns are not the same! There is a lot of hype and crap out there and you can spend a lot of $$ on a choke balun that barely does anything, or get one from MyAntennas and know it will do the job.

Wow - I just proved to myself that I needed TWO of the chokes, even *if you can't hear a problem* !!

How did I discover this? Like many swl / amateurs, I run a linear power supply and not a switching supply. So I thought things were under control with no growlers and other noise carriers walking around.

BUT, I was testing a switching supply for transmit purposes, and lo and behold on 160 and 80 meters, all the gremlins started walking around with my on-ground antennas that have a great s/n ratio, making it easier to hear a problem not being masked by noise.

Ok, fine - the best choke from myantennas for receiving the low bands CMC-0510-R is in use at the feedpoint. Still, some gremlins are making it back. Only *another* choke, this time the MFJ 915 placed near the receiver off a 3 foot jumper (never put them directly on the receiver jacks - use a small jumper) got the gremlins to nearly inaudible status.

If it wasn't for this test by purposely using a switching supply for transmit on 6 meters, and the great s/n ratio of the on-ground antenna, this problem would have been well hidden by band noise - meaning that my antenna pattern was being affected to some degree.

For nearly the same price as the 915, I'll be getting another CMC-0510-R for use near the rig as a replacement for the MFJ - even though that did work ok after the rig.

So that's going to become my standard - a choke in use near the feedpoint AND ANOTHER hanging off a small jumper near the rig. Just because you can't hear it, doesn't mean your antenna pattern is not being affected, or being unprotected from something else that may pop up later.

Yeah sure, I could use a notch filter, but I want to do it right. So TWO chokes are my minimum now, and I'll take back my statement about demonstrating an audible need for one.

 

[iMONITOR]

I've been purposely quiet for awhile. Now I want to shout from the rooftops about this remarkable device!

To be honest, I wondered if I made a big mistake and didn't know how to explaine what happened. Since receiving the CMC-130-3K 1-30MHz I made a few changes in my shack, then after hooking it up my noise level increased substantially (60 Hz hum)! I had sold my oversized MFJ power supply and replaced it with an Astron RS-12M, about half the size (12A). I also added an additional 1 foot RG8X cable in the antenna line, then I added an AOR DV-1 Digital Receiver with a noisy switching wall-wart power supply which introduced interference of it's own! I also moved some other stuff around. We've also had some wet icy weather with high humidity levels that can wreak havoc with high voltage power lines/transformers in the area. The problem was most noticalble exactly at 760 kHz (WJR AM). The problem was so bad it made listening impossible! It was so bad I wondered if WJR had some catastrophic failure!

In all the kaos I got confused over some info that prcguy gave me. Instead of inserting the CMC-130-3K on a short coax off the back of the radio, I did the opposite and mounted it on the other end, after the antenna. WRONG! After switching it the other way around as prcguy recommended, I was blown away at the improvement it made! Thanks Mike!

No wonder they said:
The common-mode filter or choke may be one of the best-kept secrets… www.ARRL.org

 

[prcguy]

I'm happy it had some kind of improvement. Usually the common mode choke is placed at or near the antenna to isolate the feedline from the antenna and reduce RF on the coax when transmitting. In some cases noise is being introduced inside the house near the radio and that travels on the shield of the coax to the antenna where its picked up and fed back to the receiver. In that case placing the choke near the radio but down the coax a few feet away from computers, switching power supplies, etc, will keep that crud from traveling up the coax.

Some of my antennas benefited from chokes at both ends and the only way to know what works is to try everything.

I've been purposely quiet for awhile. Now I want to shout from the rooftops about this remarkable device!

To be honest, I wondered if I made a big mistake and didn't know how to explaine what happened. Since receiving the CMC-130-3K 1-30MHz I made a few changes in my shack, then after hooking it up my noise level increased substantially (60 Hz hum)! I had sold my oversized MFJ power supply and replaced it with an Astron RS-12M, about half the size (12A). I also added an additional 1 foot RG8X cable in the antenna line, then I added an AOR DV-1 Digital Receiver with a noisy switching wall-wart power supply which introduced interference of it's own! I also moved some other stuff around. We've also had some wet icy weather with high humidity levels that can wreak havoc with high voltage power lines/transformers in the area. The problem was most noticalble exactly at 760 kHz (WJR AM). The problem was so bad it made listening impossible! It was so bad I wondered if WJR had some catastrophic failure!

In all the kaos I got confused over some info that prcguy gave me. Instead of inserting the CMC-130-3K on a short coax off the back of the radio, I did the opposite and mounted it on the other end, after the antenna. WRONG! After switching it the other way around as prcguy recommended, I was blown away at the improvement it made! Thanks Mike!

No wonder they said:
The common-mode filter or choke may be one of the best-kept secrets… www.ARRL.org

 

[nanZor]

I *LOVE* the myantennas CMC-0510-R especially since my interest in 160 meters has really got me going - I could never really stand to listen to the band, even with small antennas before. Things are radically different now. Just don't transmit into this rx-only one. I've got a transmit-capable version coming to replace the MFJ.

I learned about the folly of having high reactive attenuation vs real resistive attenuation in chokes before by using "Ugly Baluns". Despite having a limited bandwidth, the reactive components merely MOVED the problem instead of absorbing it. So in some cases, my noise problem was reduced, BUT now my antenna is radically worse from a pattern standpoint. So I got quieter, but only because I was pointed straight up in the pattern when the reactive choke moved the problem.

I suppose the real way is to handle it is by perfecting your grounding, but I've chased that before and not gotten very far. I'm sure the beverage guys have that down to a science. W8JI has some great info of course:

Common mode current

I hate to say it, but I'm kind of lazy when it comes to perfect grounding, so the chokes are doing great. Finding out I truly needed more than one was hidden from me until I used the on-ground antennas.

A good way to hunt of course is to listen when the band is *dead* for the gremlins. Once the band opens, even with the on-ground loop / dipole, they are still there - only to be heard a few hours later when the band goes super-quiet. Almost missed the C6 call guy in the Bahamas on 160 due to that. Fixed it today!

 

[db_gain]

I run ferrets at each end of the coax, but the ferrets closer to the rig end are more important.

 

[prcguy]

What kind of ferrites?

I run ferrets at each end of the coax, but the ferrets closer to the rig end are more important.

 

[db_gain]

I use these or similar with a mix calculated for hf and mw work;
Ham Radio Outlet Search Results

You can also just get a ferrite donut and loop the wire thru it as many times as you can, the reasoning is if you run multiple loops of conductor thru a donut you get more z increase than with multiple ferrite sleeves. Problem is if the connectors are already on the cable you get to the point where you can't put more turns on the donut. In some cases, you'd have to add dozens of ferrite sleeves to a given conductor to get the same hi z as with multiple turns around a donut of the same material.

 

[prcguy]

You have to be very specific with the ferrite type and number of turns around a doughnut. For example 9 turns of coax through a #31 mix core (FT-240-31) is a good compromise for 80 through 10m and much better than you can get with just beads over coax. Fill it up with 17 turns and its good 160m through about 30m then it drops off above that. Do 9 turns with a 52 mix core and it will be great on 10m, ok on 20m and not so good below 20m.

The best isolation I've measured with commercial choke baluns made with beads over coax is about 20dB for 40m through 10m and it drops off below 40m. 9 turns around a 31 mix torroid is close to 30dB over most of that range.

I use these or similar with a mix calculated for hf and mw work;
Ham Radio Outlet Search Results

You can also just get a ferrite donut and loop the wire thru it as many times as you can, the reasoning is if you run multiple loops of conductor thru a donut you get more z increase than with multiple ferrite sleeves. Problem is if the connectors are already on the cable you get to the point where you can't put more turns on the donut. In some cases, you'd have to add dozens of ferrite sleeves to a given conductor to get the same hi z as with multiple turns around a donut of the same material.

 

[db_gain]

The best performing hf choke I have right now has about 12 ferrite sleeves from some old Collins gear of indeterminate mix, and the rest of the coax is wrapped around a gigantor 43mix donut. I suppose a choke made from different mixes of ferrite sleeve would be better than a choke composed of two donuts of different mixes/turns due to coupling that may occur. Often you run into information that toroids are self shielding but that's not really true.