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Author Topic: Basic choke to use  (Read 375 times)

WB0LGB

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Basic choke to use
« on: December 12, 2021, 06:57:39 AM »

I'd like to keep this simple and I'm sure it's been asked a thousand times.

I have a Yaesu FT940 and vertical for 20 through 10 and the noise level is unbearable. I have no rfi filter on it at all right now so looking for the most basic solution to see if a choke will improve the situation. This isn't about the external noise sources but an attempt to try a choke.

I'd like a DIY solution so maybe a popular web page someone can point me to.

It looks like there are 2 types. One that is actually inline with the signal and another that just loops the coax around a core. What is most effective? (inline no doubt) I just want to do something at the xcvr output.

Been a long time since I've had a station set up. Years ago, didn't have the noise problem at all.
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WB0LGB

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Re: Basic choke to use
« Reply #1 on: December 12, 2021, 07:14:46 AM »

ok -- looks like these ft240 rings and some coax.
answering my own question looks like.

what's difference between the 31 and 43?

which to use for 20-10 and how many turns?    -- thanks !
« Last Edit: December 12, 2021, 07:18:10 AM by WB0LGB »
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W9IQ

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Re: Basic choke to use
« Reply #2 on: December 12, 2021, 09:53:43 AM »

Type 31 material is superior to type 43 material in an HF choking application. As you can see from the chart below, 10 to 12 turns will be optimum.

- Glenn W9IQ


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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KL7CW

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Re: Basic choke to use
« Reply #3 on: December 12, 2021, 10:01:59 AM »

Either mix should work fine for 20-10 meters, however the type 31 mix is somewhat better if you later want to use the common mode coax choke on 160,80,or 40 meters.  There are many charts on line to optimize the common mode rejection for a particular band.  However, 8 to 10 turns of something like RG58 coax should easily fit on the core without crowding the turns too much.  This should give you at least 2 S units of common mode rejection. I think the choke is a good idea for several reasons, but this may not solve your severe noise problems.  What type of vertical are you using ?  Is it resonate with a reasonable SWR on 10-20 meters.  Make sure the coax connectors, and especially the shield connection is VERY GOOD.  Is it a trap vertical ?  Is there a remote ATU at the base of the antenna, or do you have a matching network for each band at the vertical ?  Severe noise on these upper HF bands does not sound good.  Is the vertical very close to possible noise sources.  Have you tried a test with your transceiver right at the base of the vertical ?   Does your vertical require radials, if so what have you put down ?           Good Luck  Rick  KL7CW
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WB0LGB

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Re: Basic choke to use
« Reply #4 on: December 12, 2021, 10:53:29 AM »

Ok. I'm going to start with an improved coax connection. All I had time for was a prebuilt 50' cable of RG58 and I'm sure it's mediocre. Will go to RG8 or? (been a while). Will never exceed 100 watts so maybe there is now an improved coax I can use? I know for 75 ohm they're making better grade cables now. Also going to call Duke energy as there is a really bad buzzing transformer down the street. It's been like that forever. Maybe I can just take an AM radio and walk towards it to see if it's a real problem? And show them if they come out?
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WB0LGB

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Re: Basic choke to use
« Reply #5 on: December 12, 2021, 12:00:32 PM »

and what's the deal with these cores just simply having the coax wrapped around them and others I see being directly in the signal path cut and soldered in series with the inner conductor?
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W6QW

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Re: Basic choke to use
« Reply #6 on: December 12, 2021, 12:22:34 PM »

Take a look at this site (Balun Designs).  They offer a DIY UNUN kit for under $50 if you want a stand-alone common mode choke (UNUN):
 https://www.balundesigns.com/diy-kits/

Or, as you suggest, just wind your RG-58 coax through a FT-240 toroid for a $10 alternative.  The UNUN (common mode choke) will not mitigate your noise situation so I would focus on tracking that down first.

Since your coax line is just 50ft, you won't see a tangible attenuation difference using a larger coaxial cable.  Here's a chart for your information:
https://offgridham.com/wp-content/uploads/2016/04/coax-loss-chart.jpg

There are a number of enhancements that will improve your antenna efficiency, however, until you mitigate your local noise, any effort to enhance your antenna will be usurped by your receiver noise annoyance.
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KL7CW

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Re: Basic choke to use
« Reply #7 on: December 12, 2021, 07:03:54 PM »

From your description of your severe RFI on the higher bands, I think there is a very good chance that much or most of the RFI is due to actual RFI picked up by your antenna which is differential mode, so a coax (common mode) choke in that case may not help much or at all.  However, that being said, a coax choke will not hurt anything, and MAY help since you MIGHT also have some common mode RFI. Some folks always like a common mode choke at the antenna feed point, others consider it an option, since it does not always help.  I mentioned the coax shield connection as a possible problem, although I have not found it common in my 67 years as a ham and decades in the industry.  I did have a recent problem where there was a one ohm resistance in the shield connections in a coax switch.  That was enough for my coax to pick up several RFI sources inside my house as my coax snaked through my house and caused noticeable RX RFI on 160 meters. I Corrected the coax shield problem and could no longer hear this RFI since my 160 meter antennas were 30 to 250 feet from my house.  I doubt that is your problem, and I just mentioned it since you need to keep an open mind when troubleshooting noise problems.  Strange things happen.  Be sure to record your noise readings every time you change anything since often noise comes from several sources, and you need to keep track of which changes help as you "kill" the RFI one source at a time.  Happy noise hunting    Rick  KL7CW
 
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K0UA

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Re: Basic choke to use
« Reply #8 on: December 12, 2021, 07:30:05 PM »

and what's the deal with these cores just simply having the coax wrapped around them and others I see being directly in the signal path cut and soldered in series with the inner conductor?

The common mode currents in question that the choke is attempting to choke off are traveling on the "third wire" of the coax. There is current on the center conductor and current on the inside of the coax (skin effect) these are called the differential mode currents. The current traveling on the "third wire" is traveling on the outside of the coax, this is the common mode current, and we don't like it. We want to choke it off and keep it away and out of our shacks and the equipment in them.
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73  James K0UA

G4AON

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Re: Basic choke to use
« Reply #9 on: December 13, 2021, 01:30:25 AM »

I have a Yaesu FT940 and vertical for 20 through 10 and the noise level is unbearable. I have no rfi filter on it at all right now so looking for the most basic solution to see if a choke will improve the situation. This isn't about the external noise sources but an attempt to try a choke.
The way to think about your installation is from the viewpoint of the antenna... The wire that runs from your antenna to your house wiring is acting as a radial, you may see it as a coaxial feeder, but it is also a radial and as such it can both radiate RF and pick up noise. There is nothing between it and your mains wiring around the house.

Adding a few turns of coax around a ferrite ring will put a stop to the coax acting as a radial, usually you put a choke at the feed point of the antenna and ideally another one before the coax enters the shack. An FT240-31 is ideal, although for 20-10 the slightly cheaper FT240-43 works fine.

You also need to pay attention to grounding of equipment in the shack and to filtering the mains too. A lot of noise can be due to grounding arrangements (or lack of) in the shack. If you can, power the radio from a battery with no other connections except the antenna and see what noise level you have. See:
https://gm3sek.com/2019/10/11/clean-up-your-shack-2019/

73 Dave
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WB0LGB

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Re: Basic choke to use
« Reply #10 on: December 13, 2021, 06:32:59 AM »

Will start with coax and just saw RG213 which is a new one on me. Is this a higher quality than 58 -- or what is the best? Last time I bought anything it was 1975. Will run no more than 100 watts.
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W1VT

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Re: Basic choke to use
« Reply #11 on: December 13, 2021, 06:42:21 AM »

You may be thinking of RG-223, which is a double shielded coax with a  0.035 inch center conductor and 0.160 inch outer diameter. Most hams use RG-400 instead, as the Teflon dielectric will handle a lot more power than polyethylene dielectric cables.  RG-400 is a lot easier to find than RG-223.

Zak W1VT
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G4AON

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Re: Basic choke to use
« Reply #12 on: December 13, 2021, 06:48:22 AM »

Will start with coax and just saw RG213 which is a new one on me. Is this a higher quality than 58 -- or what is the best?
Replacing your RG58 with RG213 will do nothing in terms of reducing noise, unless the braid is broken or rotted.
RG213 is a larger diameter version of 58, less loss. It will be tougher than the low loss foam dialectic cables, especially if you might accidentally tread on it. It is fine for general HF use, unless you have a very long run of it.

Start with a radio running from battery power, try chokes, then and only then, resort to replacing the coax.

73 Dave
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W6QW

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Re: Basic choke to use
« Reply #13 on: December 13, 2021, 09:10:40 AM »

Will start with coax and just saw RG213 which is a new one on me. Is this a higher quality than 58 -- or what is the best? Last time I bought anything it was 1975. Will run no more than 100 watts.

RG-8 & RG-213 are virtually the same.  Both are typically used for high-power applications and/or greater lengths to your antenna and have a much greater diameter than RG-58.  The inner conductor of RG-8/RG-213 is 12 gauge and RG-58 is 20 gauge.

The design of RG-8 only allows a maximum of 4,000 volts difference between the center conductor and the shield. RG-213 allows 5,000 volts. RG-8 can withstand temperatures between -40 and +80 degrees (C), while RG-213 can only withstand between -40 and +75 degrees. Both use seven strands of wire for the center conductor, but RG213 uses slightly larger strands for an overall diameter of 0.089 inches whereas RG8 is 0.0855 inches. RG213 is slightly heavier at 10.6 lbs. for a 100-foot section whereas RG8 only weighs 10.5 lbs.

For a 50 foot coaxial run, the difference in signal strength between RG-58 & the larger RG-8 will be difficult to observe on received signals below 30 MHz.   Going to a larger coax should be lower on your enhancement priorities.
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WB0LGB

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Re: Basic choke to use
« Reply #14 on: December 14, 2021, 06:22:37 AM »

And honestly, I'm not so sure much of what I'm hearing on 20 through 10 is the bandnoise. It's been a very long time since I've had anything setup (won't mention how long) but was first licensed in 1970. I'm trying to remember what things sounded like back then with my Knight R100 rcvr but seems to me it was much, much quieter. I think also the bands were peaking at that time -- I worked much DX on 10 meter AM back then when I got home from school.

Most days, right now, 40 sounds pretty good but the minute I go to 20 the noise is generally unbearable. Even on a battery.
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