I have Fairrites 61 core, Its resistance starts to rise at about 10MHz., Inductance is good. Am I right in that it doesn't matter if there is resistance in impedance, as long as total impedance is high. I think the maximum frequency does not depend on core material.

Is there a core for higher frequency. There is a core 67 in Digikey (5967001201-ND). Is it any good. Or what is a good core material for VHF.

Balun in antenna feed point. Someone had made a balun coil from a couple turns of coaxial cable. Either the impedance of the coils is low, or their resonant frequency is on the way (too low). How to make a +j300 ohm air core coil from coaxial cable for for instance 144MHz.

Has anyone really looked at how a 1:4 balun is made from two 1:1 baluns. Inputs are in parallel. So, a common T-piece coaxial connector would work and look well. But in the output, two cables are in series, is there a neat way to connect two coaxial cables in series. And output is also balanced.

output should not be coax but two screw terminals

dg9bfc sigi

Am 13.03.2023 um 21:42 schrieb Leif M:

> I have Fairrites 61 core, Its resistance starts to rise at about
> 10MHz., Inductance is good. Am I right in that it doesn't matter if
> there is resistance in impedance, as long as total impedance is high.
> I think the maximum frequency does not depend on core material.
>
> Is there a core for higher frequency. There is a core 67 in Digikey
> (5967001201-ND). Is it any good. Or what is a good core material for VHF.
>
> Balun in antenna feed point. Someone had made a balun coil from a
> couple turns of coaxial cable. Either the impedance of the coils is
> low, or their resonant frequency is on the way (too low). How to make
> a +j300 ohm air core coil from coaxial cable for for instance 144MHz.
>
> Has anyone really looked at how a 1:4 balun is made from two 1:1
> baluns. Inputs are in parallel. So, a common T-piece coaxial connector
> would work and look well. But in the output, two cables are in series,
> is there a neat way to connect two coaxial cables in series. And
> output is also balanced.
>

Hello Leif
Maybe this article could help you with some design guidance?
<https://gm3sek.com/2018/10/17/vhf-uhf-baluns/>
73

Dave, G1OGY

On Tue, 14 Mar 2023 at 02:34, Leif M <leif.michaelsson@gmail.com> wrote:

>
> I have Fairrites 61 core, Its resistance starts to rise at about 10MHz., Inductance is good. Am I right in that it doesn't matter if there is resistance in impedance, as long as total impedance is high. I think the maximum frequency does not depend on core material.
>
> Is there a core for higher frequency. There is a core 67 in Digikey (5967001201-ND). Is it any good. Or what is a good core material for VHF.
>
> Balun in antenna feed point. Someone had made a balun coil from a couple turns of coaxial cable. Either the impedance of the coils is low, or their resonant frequency is on the way (too low). How to make a +j300 ohm air core coil from coaxial cable for for instance 144MHz.
>
> Has anyone really looked at how a 1:4 balun is made from two 1:1 baluns. Inputs are in parallel. So, a common T-piece coaxial connector would work and look well. But in the output, two cables are in series, is there a neat way to connect two coaxial cables in series. And output is also balanced.
>

It is for members only, but I got slides

Leif, ferrites are far from ideal at vhf frequencies. There are lots of resources on the web but i personally like https://g0ksc.co.uk/construction/creatingabalun.html.

Equally relevant is: Do you plan to test your balun and how will you do it?
George

I really do not understand the great amount of puzzlement over a 1:1 VHF
balun. Two simple solutions:

1) CURRENT BALUN:
A) A number of ferrite beads of appropriate material
(likely 43) slipped over the cable and spaced
aperiodically along the coaxial cable starting at the
feedpoint and commencing downward along the cable
for maybe a couple of feet.

B) Several, no more than 2, widely spaced turns of the
coax through a ferrite toroid of appropriate material
(likely 43 for 2-meters).

2) BAZOOKA BALUN:
This consists of a "pipe" (preferably copper) of
diameter that just fits over the coaxial cable left open
at the feed position and electrically bonded to the
outside of the coaxial braid 1/4-wavelength down the
coax away from the feed. The dielectric constant of
the outer coaxial insulation should be taken into
account to form the correct length of the 1/4-
wavelength "pipe".

Both of these methods have been used on 2-meters for decades.

43, 44, and 46 ferrite material is appropriate for 6 and 2-meters. Above
that, 61 material is a better choice.

Dave - WØLEV

On Wed, Mar 15, 2023 at 4:59 PM GA Chaudron <gachaudron@gmail.com> wrote:

> Leif, ferrites are far from ideal at vhf frequencies. There are lots of
> resources on the web but i personally like
> https://g0ksc.co.uk/construction/creatingabalun.html.
>
> Equally relevant is: Do you plan to test your balun and how will you do it?
> George
>
>
>

--
*Dave - WØLEV*

On Wed, Mar 15, 2023 at 06:59 PM, GA Chaudron wrote:

>
> Equally relevant is: Do you plan to test your balun and how will you do
> it?
> George

A good question. At HF it is easy, I just clip crocodile connectors to each end of the shield.
But with VHF and especially UHF that will not work. I think I just have keep wire lengths at less than 1/4 wavelength.