[TowerTalk] Ferrites 31 vs. 77 material

[Grant Saviers]

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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