So what is the "correct" way to use RF ferrite chokes? Is there a wrong way to use them? Can I damage anything by just experimenting and using them in different places on the mobile? Any disadvantages?
22racer
22racer
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RF Chokes
- Thread starter 22racer
- Start date
Ferrite cores used as chokes only affect the outside of a cable, not the inside. So, there's very little likelihood of their use affecting most circuits. I think that as long as the cable isn't breached, they won't do any harm. Want to see what happens by putting them on a cable? Do so while watching for 'normal' operations of whatever that cable affects. If you notice any unusual behavior then stop whatever it is that you're doing. I'd also observe any precautions that are normal for whatever the circuit is. If that cable handles high voltage for instance, then I'd be sure that you didn't do anything to get you 'into' that high voltage, or it into anything else. It's not just about high voltage, but that is a pretty fair example, you know?
Most of the uses of ferrite chokes deal with RF. In that regard, it almost always takes more of those ferrite chokes to do what you want than you may believe. I joke anout having a 5 gallon bucket of them, and unfortunately, sometimes it seems like it'd take that many to have any effect.
And then there's the fact that all ferrite isn't the same, most cores are made from a particular 'mix' of ferrite. Different mixes are better for different frequency ranges. I have no idea what most cores are, they aren't always labeled. So if two, three, or four aren't doing any good, it's a reasonable assumption that they aren't the right mix. Or, it takes more than you've used.
Does that tell you what you need to know about the use of ferrite chokes? Good grief no. B ut it can give you an idea of what you can chek to make them work 'better'.
This 'stuff's a lot of fun, ain't it??
- 'Doc
Most of the uses of ferrite chokes deal with RF. In that regard, it almost always takes more of those ferrite chokes to do what you want than you may believe. I joke anout having a 5 gallon bucket of them, and unfortunately, sometimes it seems like it'd take that many to have any effect.
And then there's the fact that all ferrite isn't the same, most cores are made from a particular 'mix' of ferrite. Different mixes are better for different frequency ranges. I have no idea what most cores are, they aren't always labeled. So if two, three, or four aren't doing any good, it's a reasonable assumption that they aren't the right mix. Or, it takes more than you've used.
Does that tell you what you need to know about the use of ferrite chokes? Good grief no. B ut it can give you an idea of what you can chek to make them work 'better'.
This 'stuff's a lot of fun, ain't it??
- 'Doc
Doc...just saw this....my questions are?
1, placing a core on the power leads or wrapping the power leads a few times thru a core does what?? I think it stops any stray rf from making it way into the power lines and thus into the radio? I have tried just such a wrap and can till absolutely no difference wrapped or off?
2. Wrapping a few turns of coax thru a ferrite core stops rf from being radiated by the coax shield ? Right? I cannot get the coax wraps anywhere but inside the auto or might tape one in place at the mag mount of my antenna. The question here is would it do any good at the back of the radio? What would I be able to notice? Lower noise? Or drop in swr? To know it is working?
I have couple small ones and put them on the speaker lead but ? Might be for nothing.
Operate mobile. Bonded cab, exhaust and components all to the frame. Used braided cables as short as possible. hood doors bed to frame all corners. Low noise even while running..some injector noise at times but very low...power lines are as short as possible...coax routes outside the vehicle under driver seat thru a plug to get as much outside the cab as possible. I thought about drilling the hole and thus could lace the ferrite right at the antenna base...question is would I or anyone be able to notice or measure a difference?
1, placing a core on the power leads or wrapping the power leads a few times thru a core does what?? I think it stops any stray rf from making it way into the power lines and thus into the radio? I have tried just such a wrap and can till absolutely no difference wrapped or off?
2. Wrapping a few turns of coax thru a ferrite core stops rf from being radiated by the coax shield ? Right? I cannot get the coax wraps anywhere but inside the auto or might tape one in place at the mag mount of my antenna. The question here is would it do any good at the back of the radio? What would I be able to notice? Lower noise? Or drop in swr? To know it is working?
I have couple small ones and put them on the speaker lead but ? Might be for nothing.
Operate mobile. Bonded cab, exhaust and components all to the frame. Used braided cables as short as possible. hood doors bed to frame all corners. Low noise even while running..some injector noise at times but very low...power lines are as short as possible...coax routes outside the vehicle under driver seat thru a plug to get as much outside the cab as possible. I thought about drilling the hole and thus could lace the ferrite right at the antenna base...question is would I or anyone be able to notice or measure a difference?
1, placing a core on the power leads or wrapping the power leads a few times thru a core does what??
It can stop RF too, but the primary reason is to stop any AC ('ripple', for instance) from getting 'out of' the power supply. You can consider them to be another 'filtering choke.
---
2. Wrapping a few turns of coax thru a ferrite core stops rf from being radiated by the coax shield ? Right?
That's 'right enough'. A ferrite choke does the same thing as an 'air choke' or a few coils of coax in the feed line. It stops the flow (or reduces it) of those CMCs on the outer shield. The 'best' place to put a choke is at the feed point of the antenna. Sometimes that's not possible though, so you put it where you can make it fit.
---
I have couple small ones and put them on the speaker lead but ? Might be for nothing.
A question, do you 'hear' yourself through those speakers, getting any RF interference when you transmit? If so, then putting those ferrite cores on the speaker leads may get rid of that interference. Don't get any interference in those speakers now? Then don't bother, wait till you do need to "filter" those speaker leads.
---
Which to use, multiple cores, or multiple turns through that core? The best answer is yes. To both. Which is possible to do, easiest to do, most acceptable for whatever reason? That's the one to use.
---
Operate mobile. Bonded cab, exhaust and components all to the frame. Used braided cables as short as possible. hood doors bed to frame all corners. Low noise even while running..some injector noise at times but very low...power lines are as short as possible...coax routes outside the vehicle under driver seat thru a plug to get as much outside the cab as possible. I thought about drilling the hole and thus could lace the ferrite right at the antenna base...question is would I or anyone be able to notice or measure a difference?
Good question! And the only answer I can give you is a definite, "maybe". I can't predict how much/many 'problems' you may have in one instance and then compare that to another instance.
I can say this though.
It shouldn't make any difference if that coax is inside the truck or outside the truck as far as what's inside that coax goes (signal).
If there's a choice between a 'hard mount' or a mag-mount, the 'hard mount' is the preferred way to do it. The only time a mag-mount is preferable is when you can't drill a hole. A mag-mount is not a better electrical way to do it, it's only an alternative. (About the only time a 'hole' makes a huge difference is on a submarine or a rubber balloon. Unless it's made very horribly bad, that hole makes no difference when swapping cars.)
Any of that help any?
- 'Doc
It can stop RF too, but the primary reason is to stop any AC ('ripple', for instance) from getting 'out of' the power supply. You can consider them to be another 'filtering choke.
---
2. Wrapping a few turns of coax thru a ferrite core stops rf from being radiated by the coax shield ? Right?
That's 'right enough'. A ferrite choke does the same thing as an 'air choke' or a few coils of coax in the feed line. It stops the flow (or reduces it) of those CMCs on the outer shield. The 'best' place to put a choke is at the feed point of the antenna. Sometimes that's not possible though, so you put it where you can make it fit.
---
I have couple small ones and put them on the speaker lead but ? Might be for nothing.
A question, do you 'hear' yourself through those speakers, getting any RF interference when you transmit? If so, then putting those ferrite cores on the speaker leads may get rid of that interference. Don't get any interference in those speakers now? Then don't bother, wait till you do need to "filter" those speaker leads.
---
Which to use, multiple cores, or multiple turns through that core? The best answer is yes. To both. Which is possible to do, easiest to do, most acceptable for whatever reason? That's the one to use.
---
Operate mobile. Bonded cab, exhaust and components all to the frame. Used braided cables as short as possible. hood doors bed to frame all corners. Low noise even while running..some injector noise at times but very low...power lines are as short as possible...coax routes outside the vehicle under driver seat thru a plug to get as much outside the cab as possible. I thought about drilling the hole and thus could lace the ferrite right at the antenna base...question is would I or anyone be able to notice or measure a difference?
Good question! And the only answer I can give you is a definite, "maybe". I can't predict how much/many 'problems' you may have in one instance and then compare that to another instance.
I can say this though.
It shouldn't make any difference if that coax is inside the truck or outside the truck as far as what's inside that coax goes (signal).
If there's a choice between a 'hard mount' or a mag-mount, the 'hard mount' is the preferred way to do it. The only time a mag-mount is preferable is when you can't drill a hole. A mag-mount is not a better electrical way to do it, it's only an alternative. (About the only time a 'hole' makes a huge difference is on a submarine or a rubber balloon. Unless it's made very horribly bad, that hole makes no difference when swapping cars.)
Any of that help any?
- 'Doc
Yes....thanks!
My antenna coax routing outside was to "prevent" any internal noise from inside the auto from making its way to the speaker as hum or background noise. Once I bonded cab to frame etc. I noted a greatly reduced noise levels? S5-6 down to s-1 or lower. I still hear a very slight injector noise at times....it may be the fuel pump as it is intermittent? for the most part I hear nothing that I can say is auto generated. Running auto vs auto shut off is only a slightest reduction in noise....noise I know is auto generated....most times I cannot hear any change.
I have placed a ferrite right out the back of the radio very close to the coax connector .... It makes no difference that I can here in the speaker...installed with 3-4 turns thru it or removed? In fact I feel the turns are so tight it may be compressing the coax. No noticeable difference installed or removed?
I have zero signal or sound getting back into the speaker...so that one is a waste of ferrite. Never any "feedback" if you will.
I feel with a mobile setup I must have common mode issues....thus the questions on ferrites. I may have none? But most mobile radio setups from the reading I have done have CM issues.
Focus is to have a clean signal....no noise attached and reduce any noise on the receiver side if possible.
My antenna coax routing outside was to "prevent" any internal noise from inside the auto from making its way to the speaker as hum or background noise. Once I bonded cab to frame etc. I noted a greatly reduced noise levels? S5-6 down to s-1 or lower. I still hear a very slight injector noise at times....it may be the fuel pump as it is intermittent? for the most part I hear nothing that I can say is auto generated. Running auto vs auto shut off is only a slightest reduction in noise....noise I know is auto generated....most times I cannot hear any change.
I have placed a ferrite right out the back of the radio very close to the coax connector .... It makes no difference that I can here in the speaker...installed with 3-4 turns thru it or removed? In fact I feel the turns are so tight it may be compressing the coax. No noticeable difference installed or removed?
I have zero signal or sound getting back into the speaker...so that one is a waste of ferrite. Never any "feedback" if you will.
I feel with a mobile setup I must have common mode issues....thus the questions on ferrites. I may have none? But most mobile radio setups from the reading I have done have CM issues.
Focus is to have a clean signal....no noise attached and reduce any noise on the receiver side if possible.
"The 'best' place to put a choke is at the feed point of the antenna"
"FEEDPOINT" being near the bottom of the antenna mast or the feedpoint near the radio? I have a mag mount Wilson 5000 with the coax routed into the cab at the third brake/cab light. Could an "air choke" possibly be beneficial just inside the cab, resting just behind the cab/brake light?
"FEEDPOINT" being near the bottom of the antenna mast or the feedpoint near the radio? I have a mag mount Wilson 5000 with the coax routed into the cab at the third brake/cab light. Could an "air choke" possibly be beneficial just inside the cab, resting just behind the cab/brake light?
Feedpoint is at the antenna, and the goal of
a choke of the type you are asking about is
to stop or reduce common mode current from
following the coax back in the pickumuptruck.