Hi Grant,
Thank you for that information. I assume that the 1000 ohm choking resistance
was for the entire dozen beads not just one bead, correct?
What is the recommended choking resistance goal? Is it 5 – 6 K ohms? If not,
what in your opinion is the minimum effective resistance goal?
Is it 5 – 6 K ohms from 1.8 – 30 Mhz or is it a difference amount above 3.5 Mhz?
Tnx & 73
Bob KQ2M
From: Grant Saviers
Sent: Thursday, November 07, 2019 1:35 PM
To: Bob Shohet, KQ2M ; towertalk@contesting.com
Subject: Re: [TowerTalk] Ferrites 31 vs. 77 material
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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