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Re: [TowerTalk] Ferrites 31 vs. 77 material

To: "Bob Shohet, KQ2M" <kq2m@kq2m.com>, towertalk@contesting.com
Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material
From: Grant Saviers <grants2@pacbell.net>
Date: Thu, 7 Nov 2019 10:35:10 -0800
List-post: <mailto:towertalk@contesting.com>
I measured about a dozen of these size beads on RG8 and found a choking resistance under 1000 ohms, IIRC. This was for a passive receive 160m 4 square (W8JI design - top hats, L resonated, R loaded) and we decided a K9YC design was what was needed.

So the answer is "a lot".

OTOH, 9 form disciplined turns of FEP RG179 75 ohm (micro) miniature TFE coax on the same ferrite yields 5 to 6k ohms on 160 and 80. I'm using this design for DHDL receive antenna chokes. Probably ok to 600w on 160/80 so the larger size FEP 75 ohm coax on a 240 core makes more sense for a Tx 4 square.

Grant KZ1W

On 11/6/2019 6:28 PM, Bob Shohet, KQ2M wrote:
This has been an interesting tangential discussion but I would like to now 
bring it back to my original question......  :-)

So far, taking into account the tolerance caveats, the consensus seems to be to 
use 31 material going forward rather than 77 material.

I prefer to use large ferrite beads that fit on the coax ??? roughly 1/2??? ID 
-  1??? OD  x 1 1/4??? height and then tape the beads in place in physical 
proximity  to each other next to the feedpoint.

All coaxial cables used for 4 ???square phasing lines are cut for an electrical 
1/4 wavelength   (RG11 Foam)
All coaxial feedlines from the antenna to the radio are cut for a multiple of 
an electrical 1/2 wavelength.  (RG213 or Buryflex)
For the 40 meter wirebeam I use an electrical 1/2 wavelength of RG8X followed 
by 1 wavelength of Buryflex.

In order to provide enough resistance adequate for an effective choke,  how 
many 31 beads should I used on each phasing line or feedline for

1.8 mhz?
3.6 mhz?
7.1 mhz?
14 mhz?
21 mhz?
28 mhz?

That is for the feedlines and the phasing lines.  But what I have also read is 
that I should also be using ferrite beads at the amp input and amp output.  
Have I understood this correctly?  Should I then also use beads at the output 
of the radio?  Should these beads also be 77 material?

Is there any issue if the antenna beads are one type of material (43) and then 
you use 77 material for the amp/radio inputs/outputs?

Thanks in advance for your help!

73

Bob  KQ2M
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