[hpsdr] Possible added feature request

[radio at netins.net]

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,  W0GN

On 2020-11-03 1:01 pm, Helmut Oeller wrote:

> ***** High Performance Software Defined Radio Discussion List *****
> 
> Both ideas/approaches are unworldly. While the implementation of a VNA software is no big deal, a hardware reflection bridge has to be inserted and in particular calibrated. 
> 
> But even when you get a reasonable result of R and jX  at your radio input, it's not enough information for an automatic tuner: the tuner's position in the feedline and the length of the feedline determines the necessary transformation. It would be much easier to utilize the SWR, e.g. available at a bidirectional coupler, used for the PS feedback loop. 
> 
> 73, Helmut, DC6NY 
> 
> Am 03.11.2020 um 17:55 schrieb Scott Traurig: 
> 
> ***** High Performance Software Defined Radio Discussion List *****
> 
> There was work in this regard done a long time ago but it is hopelessly stale and it also requires additional hardware: 
> 
> https://openhpsdr.org/wiki/index.php?title=VNA 
> 
> It would undoubtedly be easier to adapt a NanoVNA. Not only is the hardware ready to go, the software is simpler and a lot more accessible. It would be easy to embed in a home brew tuner: 
> 
> https://openhpsdr.org/wiki/index.php?title=VNA 
> 
> Finally, it's worth noting that the only tuner on the market that actually makes a complex impedance measurement and jumps right to the exact answer in one step is the MFJ-939. If MFJ made a legal limit version of that tuner I'd buy it in a heartbeat. 
> 
> 73, 
> 
> Scott/w-u-2-o 
> 
> On Tue, Nov 3, 2020 at 11:32 AM <radio at netins.net> wrote: 
> Pure signal uses one RX channel to provide feedback.
> 
> Is it possible to use an RX channel to determine just the phase and 
> resistance of the RF signal in the antenna system feed point?  If so, 
> this could be used to automate a home brew antenna coupler.
> 
> John,  W0GN 
> 
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