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#1
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ferrite balun grades
Any advice on which grade of ferrite would be most useful for a
feeedline balun choke effective at 70 cm? Thanks de miken zl1bnb |
#2
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ferrite balun grades
Mike Newman wrote:
Any advice on which grade of ferrite would be most useful for a feeedline balun choke effective at 70 cm? #68 material might work although I have never tried it. -- 73, Cecil http://www.qsl.net/w5dxp |
#3
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ferrite balun grades
"Mike Newman" wrote in message ... Any advice on which grade of ferrite would be most useful for a feeedline balun choke effective at 70 cm? Thanks de miken zl1bnb Hi Miken I've been using the tubular, high permeability ferrites designed for RFI suppression slipped over the RG-223 coax for a balun for vhf antennas. I am aware of the high loss with those ferrite tubes. I have been hoping the high permeability would present a high reactance to currents along the outside of the coax. So far, the tubes are working OK for my needs. Your mileage may vary. Jerry |
#4
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ferrite balun grades
On Tue, 07 Mar 2006 15:18:33 GMT, "Jerry Martes"
wrote: "Mike Newman" wrote in message .. . Any advice on which grade of ferrite would be most useful for a feeedline balun choke effective at 70 cm? Thanks de miken zl1bnb Hi Miken I've been using the tubular, high permeability ferrites designed for RFI suppression slipped over the RG-223 coax for a balun for vhf antennas. I am aware of the high loss with those ferrite tubes. I have been hoping the high permeability would present a high reactance to currents along the outside of the coax. So far, the tubes are working OK for my needs. Your mileage may vary. Jerry That's exactly what I intended doing, feeding a moxon rectangle in this case, my win4nec model gives 50+0.1j. Given the correct grade of ferrite, it should probably be ok on UHF. But how to to determine the effectiveness? Maybe a small bead with a couple of turns to pick up voltage nodes on the coax feedline, with and without the choke balun beads. MikeN |
#5
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ferrite balun grades
"Mike Newman" wrote in message ... On Tue, 07 Mar 2006 15:18:33 GMT, "Jerry Martes" wrote: "Mike Newman" wrote in message . .. Any advice on which grade of ferrite would be most useful for a feeedline balun choke effective at 70 cm? Thanks de miken zl1bnb Hi Miken I've been using the tubular, high permeability ferrites designed for RFI suppression slipped over the RG-223 coax for a balun for vhf antennas. I am aware of the high loss with those ferrite tubes. I have been hoping the high permeability would present a high reactance to currents along the outside of the coax. So far, the tubes are working OK for my needs. Your mileage may vary. Jerry That's exactly what I intended doing, feeding a moxon rectangle in this case, my win4nec model gives 50+0.1j. Given the correct grade of ferrite, it should probably be ok on UHF. But how to to determine the effectiveness? Maybe a small bead with a couple of turns to pick up voltage nodes on the coax feedline, with and without the choke balun beads. MikeN Hi Mike Since you are acknowledging the existence of 1/10th of an ohm of inductive reactance, at UHF, you are way beyond my level of accuracy in any measurement of effectiveness. But, I once measured the inductance across the ferrite tube by connecting the impedance "meter" to the exposed ends of the coax braid that was threaded thru the center of the ferrite. Then I removed the ferrite and repeated the test with the ferrite removed. Roy Lewallen has an excellant paper written to show how to properly evaluate baluns. I have the paper saved and will be happy to share it with you. It is almost a *must read* since it is so thouough and informative. Jerry |
#6
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ferrite balun grades
On Wed, 08 Mar 2006 16:16:58 +1300, Mike Newman
wrote: But how to to determine the effectiveness? Maybe a small bead with a couple of turns to pick up voltage nodes on the coax feedline, with and without the choke balun beads. Hi Mike, Good start, keep it simple. This presumes you have the material, but don't know its type (s/b #43 or #64): Take a short transmission line from your rig; pass the center conductor through ONE bead; and bring it back and short it to the shield; transmit on the 5W range for as long as it takes to read SWR. You should get a reading of roughly 1.3:1 to 2:1 for the right material - and - depending on how long you held down the transmit, it should get toasty warm to blistering hot. 73's, Richard Clark, KB7QHC |
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