[hpsdr] Possible added feature request

[Helmut Oeller]

Scott, your reference suffers from a fundamental design fault: The balun
between the LC network and the symmetrical input port will not work as
expected or provide suffient common mode rejection (> 30 dB) on the 50
ohms coax side. The balun needs for efficiency a constant Z. Either you
spend a symmetrical LC network or let a unsymmetrical LC combination
float. But in each case the balun has to be placed at the 50 ohms side.

BTW bidirectional couplers with 5 octaves bandwidth are available from
different manufacturers and vendors. Keep in mind that the directivity
of the coupler should be > 20dB.

73, Helmut, DC6NY

Am 04.11.2020 um 04:31 schrieb Scott Traurig:
> ***** High Performance Software Defined Radio Discussion List *****
>
>
> There are plenty of examples of how to do this. Building the requisite
> coupler is not difficult. You can buy them from Xtronic.
>
> Here's a more relevant example:
> https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1191&context=eesp
> <https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1191&context=eesp>
>
> Incorporating something like a NanoVNA into this design, and changing
> the software to calculate the required L and C directly instead of
> iteratively should be possible.
>
> This could also be accomplished using a link coupled topology if you
> prefer.
>
> 73,
>
> Scott/w-u-2-o
>
> On Tue, Nov 3, 2020 at 2:38 PM <radio at netins.net
> <mailto:radio at netins.net>> wrote:
>
>
>     Using SWR is done when tuning L networks, but would like to try
>     adding stepper motors to a Johnson Viking Matchbox so I can use it.
>
>     I can't seem to come up with a method to tune for minimum SWR.  I
>     suppose one would adjust first the tuning and step the loading one
>     way or the other and use the low SWR position to hold for the next
>     iteration.  Then repeat that process over and over.
>
>     I have been told it is quite difficult to make a directional
>     coupler that works well over the 160 - 6m range, but a calibration
>     file could be made at the antenna system feed point (input side of
>     Matchbox) that might get a close enough calibration to use for
>     tuning.
>
>     John,  W0GNhpsdr-openhpsdr.org/
>     <http://lists.openhpsdr.org/pipermail/hpsdr-openhpsdr.org/>
>
>
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