Topband: The Magic-T

[Jorge Diez - CX6VM]

Hello

KD9SV made a great Magic T

https://www.dxengineering.com/parts/svp-sv-rsc

73,
Jorge
CX6VM/CW5W

El mar, 9 feb 2021 a las 23:02, Lee STRAHAN (<k7tjr at msn.com>) escribió:

> Hi Low Band people,
>    Nice presentation Steve. I would like to point out that Beverage users
> or even other phased antenna users should not use paralleling two 75 ohm
> coaxes and then matching them back to 75 for the receiver. While on the
> surface that all sounds good there is a little problem for the individual
> antennas. If you look from the wire through the Beverage transformer to the
> parallel junction the antenna transformer actually sees the other antenna
> at 75 ohms in parallel with the rig matching transformers 75 ohms. This
> causes the real load impedance on the Beverage transformer to be 37.5 ohms
> and not 75. This may cause the Beverage to not have the anticipated
> impedance flat curve or possible performance problems. This could also make
> the end load resistor not be an anticipated value. If you use a delay line
> in one antenna for stagger, the following should be noted. It has been my
> experience that although theoretically you only need to match at least one
> end of a coax for the phase delay in circuit to match the proper terminated
> value, I have found that terminating both ends reduces problems from
> component tolerances not terminating the proper coax impedance causing
> unwanted phase shifts. Using a Magic Tee will help terminating the coaxes
> with their proper impedance keeping the phase delay where you expect it.
> Early designers of passive 4 or more element receiving arrays missed this
> point when making combiners for arrays using paralleled transmission lines.
>    Bottom line is to yes yes, use a Magic Tee or some version of a hybrid
> combiner for combining which will isolate between  antennas.. Then the
> antennas as well as the receiver will see the 75 ohm load as likely
> designed.
>  Here is a nice technical tutorial on the Magic Tee.
> https://michaelgellis.tripod.com/magict.html
> Lee  K7TJR  OR
>
> -----Original Message-----
> From: Topband <topband-bounces+k7tjr=msn.com at contesting.com> On Behalf Of
> donovanf at erols.com
> Sent: Tuesday, February 9, 2021 3:28 PM
> To: topband <topband at contesting.com>
> Subject: Re: Topband: The Magic-T
>
>
> This is the corrected URL for Steve's Magic-T video
>
>
> www.youtube.com/watch?v=_Bbt1IcC4bk
>
>
> 73
> Frank
> W3LPL
> ----- Original Message -----
>
> From: "VE6WZ_Steve" <ve6wz at shaw.ca>
> To: "topband" <topband at contesting.com>
> Sent: Tuesday, February 9, 2021 10:29:54 PM
> Subject: Topband: The Magic-T
>
> Today I uploaded a video to my RX series which explains the Magic-T
> combiner.
> I have received a few emails asking me “how do I make the magic-T”? so I
> thought a video would be helpful.
>
> I show the method for winding and building the Magic-T combiner and I
> explain how it is used in phased RX antennas.
> The associated 2:1 impedance transformer is discussed, and I show the
> difference between an isolated and auto-transformer architecture.
>
> I also discuss an error that can be made when building phased RX antennas
> if care is not taken to avoid an unintentional 180 phase shift at one of
> the elements, especially if using home-brew matching boxes.
>
> YouTube video: https://youtu.be/_Bbt1IcC4b <https://youtu.be/_Bbt1IcC4b>-
>
> 73, de steve ve6wz
> _________________
> Searchable Archives: http://www.contesting.com/_topband - Topband
> Reflector
>
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> Reflector
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> Reflector
>


-- 
73,
Jorge
CX6VM/CW5W