Warm Snap On Ferrite Beads

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by N0KTB, Jul 31, 2020.

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  1. N0KTB

    N0KTB Ham Member QRZ Page

    Hi, Jeff.

    They were comfortable to hold. But, noticeably warm ... well above ambient. They are snap-on so they are in a plastic case, as well.

    I went back and looked at my WSTJ-X log: My final push was 6 FT-8 contacts in about 12 minutes. Running around 50-watts. And, I know that not every one of my transmissions went through the first try. So, I would say I was probably transmitting 15 seconds at a time with a 15-second break for a 12 minute duration.

    Adam - N0KTB
     
  2. K7JOE

    K7JOE Ham Member QRZ Page

    adam, the inverted L acts similarly to a 1/4 lambda "ground plane" antenna and needs a counterpoise of 1/4 lambda to work against. Simply add 21 to 22 feet of wire to the existing 12 foot ground plane radials to get them to approx 33 feet each (1/4 lambda for 40 meters). The length does not need to be exact. That will significantly reduce the common mode currents on the outside of the coax (right now, the coax is acting as the opposing 1/4 lambda radial since none of the existing 12 feet radials are long enough.

    Even with radials, keep the beads in place - doing so may further reduce common mode by decoupling the feed line from the antenna and by doing so, will REALLY keep the man made noise on the system down by not allowing the coax to pick up noise as it makes it's way from the antenna into the hamshack and into your HF rig.

    Adding the radials, you'll find this antenna is very effective on 40M, especially for DX work (lower angles).
     
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  3. N0KTB

    N0KTB Ham Member QRZ Page

    Thank you for the reply and advice. It is easy enough for me to add wire to the end of the radials. I have some quick connects that I can use to extend and shorten the radials between the 40m and 15m version of the antenna. That will be my next round of experiments.

    Thanks again.

    Adam - N0KTB
     
  4. K7JOE

    K7JOE Ham Member QRZ Page

    A tip: The radials at 33ft (for 40 M) will act very well as radials for 15M, no need for separate length radials. That's the magic of odd-harmonics. 15M is the 3rd harmonic of the 40M band. The 15M antenna should work just as well with the 40M radials as the 15M radials in place.

    Keep us posted of your actual results !
     
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  5. N8CMQ

    N8CMQ XML Subscriber QRZ Page

    Sorry to take so long getting back.

    As the beads are turning RF into heat, the reason is usually because you need better ground plane to stop the current from flowing where you don't want it. As you already heard from the others and are working on it, it will be interesting to find out what you do to correct the issue.
     
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  6. KM1H

    KM1H Ham Member QRZ Page

    What size are the beads and what coax are you using?

    Ive used slide over RG-213 size coax 43 mix beads (Fair-Rite 2643102002) for over 30 years at 1200-1500W on 40-10M yagis and 80 and 160 wires and phased verticals and never noticed any heat. BUT when snap ons became popular around the same time I found them rather useless for common mode on coax and pretty much resulted in very poor directivity switching and also suppression on computer, etc. cables.

    Dont mess with the elevated radials other than to lengthen for 40; just two may be enough, let them alone to do their job. You can also lay down a galvanized wire mesh on the ground but not connected to anything. About 1/8 wavelength in all directions at the lowest frequency but not that critical. It will stabilize the ground loss at the base of the antenna in all weather conditions. Use 2x4 mesh either bare or plastic coated where rusting is prevalent. Wrapped chicken wire might be OK for a long time in the desert or a cheap throw away as needed elsewhere.

    Ive used elevated radials 160-80 starting in 1989 and they have allowed me to win DX and WPX contests, work well over 300 DXCC entities on CW/SSB. I now have homebrew elevated radial verticals for 40/30, 20/17, and 15/12/10 to use with the vintage tube gear on AM/SSB/CW that do extremely well even at ~100W. Simple to build.

    Carl
     
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  7. N0KTB

    N0KTB Ham Member QRZ Page

    N8CMQ and K7JOE:

    Thanks for the replies. I keep thinking that I will get back out there when it cools down and do some more experimenting. It has been too blasted hot in Texas to fiddle with it. This weekend won't be much better, but maybe I can get out tomorrow morning while it is cool.

    I am going to add length to get 40m radials and go from there. The horizontal part of my "L" will have to be shortened since I was originally using ground radials sized for 15m. I had an OCF inverted L, or something (longer inverted L length, shorter radials, feedpoint was way off-center). I have been modeling the antenna on 4NEC2 to get the correct horizontal length of wire with using radials sized for 40m, and I never could get the SWR below 2 with an antenna impedance of around 25 ohms. Then I started looking online at inverted-L design and apparently 25 ohms is not far off.

    I'll keep the group updated. I appreciate the replies!

    Adam - N0KTB
     
  8. N0KTB

    N0KTB Ham Member QRZ Page

    Hi, Carl.

    I am using a 50-ft section of new RG-8X. From the DX Engineering Website, the bead dimensions: 0.62" OD, 0.25" ID, 1.2" length. They are Mix-31 snap-ons.

    DX Engineering doesn't have any real data on the impedance, but from other sources I think they are about 100 ohms per bead at 7-mHz. I have (5) five on the current antenna. I am guessing a better option would be creating a choke from a toroid donut.

    I plan on trying 2 elevated radials for 40m. I'll keep you updated. Thanks for your reply!

    Adam - N0KTB
     
  9. KM1H

    KM1H Ham Member QRZ Page

    Adam, DXE isnt good at much in the way of details but great at overpricing.

    Use a Fair Rite 2643803802 from Mouser (their photo is wrong, look at the dimensions listed.

    I suggest reading these thoroughly to the last page as it can get confusing and use the RG-8x for up to "maybe" 100W for winding the choke and RG-400 or other Teflon versions for QRO. Short lengths of Teflon cables are common on Ebay at good prices.

    http://audiosystemsgroup.com/RFI-Ham.pdf

    http://audiosystemsgroup.com/2018Cookbook.pdf

    I use stacked cores and dont jam up the turns and shoot for ~ 5000 Ohms. 500 t0 1000 was considered fine decades ago but is no longer valid.

    Carl
     
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  10. KF5LJW

    KF5LJW Ham Member QRZ Page

    Nothing changes with RF
    The laws of physics do not change from mechanical to electrical energy. RF is electrical energy and the laws of physics still applies. If your beads are getting warm means they are burning off power as Waste Heat just like mechanical or electrical energy.
     
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