Felipe,
I just now built & tested what you need.
I tried 7 & 8 turns, but it resolved too high in freq.
Use 9 TURNS on a core-stack of five (5) of P/N 2631803802 cores. That’s the
Mix #31 core.
For the choke windings, make the windings VERY tight to the core-stack.
To do that, you will need 79 INCHES of RG-58/U – for the windings alone.
ADD to that what you need for a pigtail and connectors.
Here is what I measured after I built the above.
As measured on my DG8SAQ VNWA Vector Network Analyzer:
1.8 MHz Zmag = 12,230 Ohms, Rs = 9,201 Ohms, 41.8 dB Common Mode Attenuation
1.9 MHz Zmag = 13,211 Ohms, Rs = 10,831 Ohms, 42.47 dB Common Mode
Attenuation
2.0 MHz Zmag = 14,083 Ohms, Rs = 12,414 Ohms, 43.03 dB Common Mode
Attenuation
Put the choke close to the 9:1 matching device. 1 Foot from the 9:1 will be
fine.
If you want to, add another choke (9T on 5 Cores) 1 foot from the switch box.
If you have any questions, please email me:
N3RR (at) erols.com
I can email you the frequency plot from my VNWA if you want it.
Please let me know how this works for you.
73 & GL!
Bill N3RR
_____
From: "Filipe Lopes" <ct1ilt@gmail.com>
To: "JC" <n4is@comcast.net>
Cc: "topBand" <topband@contesting.com>
Sent: Monday, October 12, 2015 1:51:43 PM
Subject: Re: Topband: Commond mode choke for Beverage
Hello JC,
Thanks for your answer.
I just ordered a few 2631803802 and 5943003801 from mouser.
With these ferrites I ask the same question, should I put the choke close
to the 9:1 Balun or near the switching box and how many turns? some bevs
have the feed point at +- 60m away from the switching box.
73's Filipe Lopes
CT1ILT - CR6K
F4VPX - TM3M
2015-10-12 15:40 GMT+02:00 JC <n4is@comcast.net>:
> Hi Filipe
>
> Zero , you should use material #31 or #77 , The core you have is not good
> for low bands.
>
> JC
> N4IS
> -----Original Message-----
> From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Filipe
> Lopes
> Sent: Monday, October 12, 2015 8:46 AM
> To: topBand <topband@contesting.com>
> Subject: Topband: Commond mode choke for Beverage
>
> Hi guys,
>
> I am about to add a common mode choke to isolate the antenna from its
> feedline to each of my beverages and I only have FT240-61 ferrites. My
> question is how many turns should I do on the ferrite using RG58 (all my
> bevs are fed with RG58). Also should I put the choke near the 9:1 balun or
> near my bev switching box?
>
> Thanks in advance.
>
> 73's Filipe Lopes
> CT1ILT - CR6K
> F4VPX - TM3M
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>
>
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