Recommendations for a Good Quality Antenna Mounted Common Mode Choke?

[Merovingian]

I'm currently working on taming the RF noise covering all of the frequencies I can receive with my three SDRs. I've identified my UPS as the primary noise source, I've bought several hundred dollars worth of ferrite rings of various materials covering a few kHz through 1 GHz and several lengths of LMR 100, 195 and 200 to wrap around the various ferrite ring stacks. They didn't help, one or two seem to make the noise audibly worse. I'm planning to replace my UPS with two or three new ones that have very low noise since the ferrite chokes didn't really work. I'll have to work on that later on. . . .

In the mean time I want to put some common mode chokes out at my HF, VHF and UHF antennas to try to lower the noise from that end as well. Can anyone recommend good quality premade common mode antenna chokes? I was looking at this one:

WiNRADiO Direct Order Shop

They seem to make good SDR radios, I would hope their chokes are as good. I know that one could probably be built "cheaper" but what I have done so far hasn't worked out well and I want something that has been designed, built and tested and known to be "good". Something that will reduce the noise as much as possible. Anyone know of anything better?

Thanks

 

[jonwienke]

A common-mode choke won't help if the RFI is getting in via the antenna, as opposed to the coax shielding.

 

[prcguy]

The best common mode RF chokes I know of are made by MyAntennas. They publish specs which are really good where other companies don't even know how to test their products to get a spec. They have models for VLF/HF receive only and HF/VHF transmit and receive. They are way more effective than something you can make, unless you really know what your doing and have test equipment to optimize it.

Common Mode Choke

We offer Common Mode Chokes / Noise Suppressors / Line Isolators / RFI eliminators for antenna systems operating from 1.8-50 MHz, Our products are broadband units covering a huge portion of the fre…

myantennas.com

 

[Merovingian]

Thanks for the information, I'll take a look. I was planning to put them at the receiver and the antenna. It seemed to be effective from some of the videos and pages I've seen. Is it really necessary at the antenna? Or is the receiver end good enough? I would think both, but I'm still learning as I go.

Also, is it very effective for VHF and UHF? I haven't seen much in the way of chokes for VHF and UHF receivers.

Thanks again for all of your help.

The best common mode RF chokes I know of are made by MyAntennas. They publish specs which are really good where other companies don't even know how to test their products to get a spec. They have models for VLF/HF receive only and HF/VHF transmit and receive. They are way more effective than something you can make, unless you really know what your doing and have test equipment to optimize it.

Common Mode Choke

We offer Common Mode Chokes / Noise Suppressors / Line Isolators / RFI eliminators for antenna systems operating from 1.8-50 MHz, Our products are broadband units covering a huge portion of the fre…

myantennas.com

 

[prcguy]

Every antenna and radio setup will be different, some might see a big reduction in noise by installing RF chokes at the antenna and/or radio end where others may not see any change.

I originally saw an improvement on a ZS6BKW dipole where I had a home made choke with a single FT-240-31 ferrite core and about 9 turns of coax around it at the ladder line coax junction and I replaced it with a very effective one like the big MyAntennas CMC-250-5K here: CMC-230-5K 2-30MHz. My noise floor in general went down a few dB and many birdies and noise humps were reduced. Adding a second choke (MyAntennas CMC-130S-3K) at the radio end made further but slight reduction in birdies and noise humps. I suspect if I had gone from no choke to the MyAntennas chokes instead of starting with my home made one the improvements would have been greater.

It would be nice if you could borrow an effective choke and test before buying.

Thanks for the information, I'll take a look. I was planning to put them at the receiver and the antenna. It seemed to be effective from some of the videos and pages I've seen. Is it really necessary at the antenna? Or is the receiver end good enough? I would think both, but I'm still learning as I go.

Also, is it very effective for VHF and UHF? I haven't seen much in the way of chokes for VHF and UHF receivers.

Thanks again for all of your help.

 

[Merovingian]

Thanks yet again for the information, I appreciate it. Yeah it would be nice if I had an effective choke to test, unfortunately I will have to buy my own to know for sure.

Every antenna and radio setup will be different, some might see a big reduction in noise by installing RF chokes at the antenna and/or radio end where others may not see any change.

I originally saw an improvement on a ZS6BKW dipole where I had a home made choke with a single FT-240-31 ferrite core and about 9 turns of coax around it at the ladder line coax junction and I replaced it with a very effective one like the big MyAntennas CMC-250-5K here: CMC-230-5K 2-30MHz. My noise floor in general went down a few dB and many birdies and noise humps were reduced. Adding a second choke (MyAntennas CMC-130S-3K) at the radio end made further but slight reduction in birdies and noise humps. I suspect if I had gone from no choke to the MyAntennas chokes instead of starting with my home made one the improvements would have been greater.

It would be nice if you could borrow an effective choke and test before buying.

 

[Ubbe]

The coax shield are a good conductor and will direct any RFI it picks up to either end of the coax. If the receivers shielding are good then it isn't necessary to try and block the RFI, but many scanners have bad shielding and can even pick up transmitters without any antenna connected. But the RFI signal also goes up to the antenna and enters that way and needs to be stopped before it comes near the antenna.

It also has a double puprose at the antenna end if your antenna systems isn't perfectly match to the unbalanced coax. If you have a common mode choke at the antenna it will stop the coax from being part of your antenna system.

/Ubbe

 

[Merovingian]

I ordered:

1 CMC-0510-R 0.5-10MHz BNC
1 CMC-130-3K 1-30MHz
1 CMC-154-3K 1-54MHz
2 CMC-VHF-2K 110-180MHz

Plus associated adapters and short lengths of cable for my antennas.

I hope this will work well. I've spent a ton on chokes. . .

 

[prcguy]

I need to talk with Danny at MyAntennas about a sales commission.

$$$$$

I ordered:

1 CMC-0510-R 0.5-10MHz BNC
1 CMC-130-3K 1-30MHz
1 CMC-154-3K 1-54MHz
2 CMC-VHF-2K 110-180MHz

Plus associated adapters and short lengths of cable for my antennas.

I hope this will work well. I've spent a ton on chokes. . .

 

[Merovingian]

Hahahahaha You probably should.

I need to talk with Danny at MyAntennas about a sales commission.

$$$$$

 

[prcguy]

Checking back on this, did you get the chokes and was there any improvement?

 

[cmdrwill]

Maybe I missed this, did you choke the UPS? As you mention the UPS as the source of the interference.

Got's to choke it at the source.

 

[Merovingian]

Hi. I've been gone all day. Just got home. . .

Yes, I got all of the chokes. I've tried the chokes for the shortwave frequencies, either one at a time or both together in series (0.5-10 and 1-30) at the receiver end and didn't notice any change at all. At least it didn't seem to make the noise worse like one of my home made chokes did. It has been raining a lot for the last few weeks so I haven't had a chance to install any chokes at the antenna end. I don't know if installing at both ends will make any more difference since the receiver end didn't make any difference.

I've replaced my big UPS with two smaller RF quiet UPS's, which helped a good bit. I did find an AC adapter behind my home theater system that was gushing RF noise, like huge noise. Once I unplugged it a lot of RF noise went away. I've got some more testing to do when I have some more time. I've noticed that there is still a good bit of noise between 100kHz and 15MHz but WWV on 5MHz is audible where as before there was so much buzz it just swamped everything. I was really hoping that adding these chokes would take care of the rest of the remaining noise so that all of the frequencies would be stone silent.

I know it is impossible to help from your end since you are not here but do you have any thoughts on eliminating the remaining noise? So far I've shut off all of the breakers except the room where the computer is, it didn't change anything hardly at all. Next I started unplugging AC adapters one at a time under my computer desk and behind my theater system one by one. I unplugged one, didn't make any difference so I plugged it back in. I did that for every AC adapter in the room but that did make any noticeable change. I still have to try putting my snap on chokes on the USB cable to see if that helps. My plasma TV puts off a good bit of noise when its on, I'm not sure if putting a choke on it's power cord will help much if the plasma screen is emitting the noise. . . All kinds of noise, everywhere I never noticed until I got a SW radio. . .

Checking back on this, did you get the chokes and was there any improvement?

 

[Merovingian]

I replaced my old UPS with a couple far more RF quite UPSs. It is not very quiet when it is running on battery power but I don't expect to be using the radios when I'm in that situation. I'll have to try putting a choke on them to see if that makes any more difference, I'm kind of doubting it though. I've spent many hundreds of dollars on chokes of all kinds and materials so I have a lot to experiment with and test with.

Maybe I missed this, did you choke the UPS? As you mention the UPS as the source of the interference.

Got's to choke it at the source.