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<br /><br />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.<br /><br />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.<br /><br />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. <br /><br />John, W0GN<br /><br />
<p id="reply-intro">On 2020-11-03 1:01 pm, Helmut Oeller wrote:</p>
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<p>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.</p>
<p>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.</p>
<p>73, Helmut, DC6NY</p>
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<div class="v1moz-cite-prefix">Am 03.11.2020 um 17:55 schrieb Scott Traurig:</div>
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<div>There was work in this regard done a long time ago but it is hopelessly stale and it also requires additional hardware:</div>
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<div><a href="https://openhpsdr.org/wiki/index.php?title=VNA" target="_blank" rel="noopener noreferrer">https://openhpsdr.org/wiki/index.php?title=VNA</a></div>
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<div>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:</div>
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<div><a href="https://openhpsdr.org/wiki/index.php?title=VNA" target="_blank" rel="noopener noreferrer">https://openhpsdr.org/wiki/index.php?title=VNA</a></div>
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<div>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.</div>
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<div>73,</div>
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<div>Scott/w-u-2-o</div>
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<div class="v1gmail_attr" dir="ltr">On Tue, Nov 3, 2020 at 11:32 AM <<a href="mailto:radio@netins.net" rel="noreferrer">radio@netins.net</a>> wrote:</div>
<blockquote class="v1gmail_quote" style="margin: 0px 0px 0px 0.8ex; border-left: 1px solid #cccccc; padding-left: 1ex;"><br />Pure signal uses one RX channel to provide feedback.<br /><br />Is it possible to use an RX channel to determine just the phase and <br />resistance of the RF signal in the antenna system feed point? If so, <br />this could be used to automate a home brew antenna coupler.<br /><br />John, W0GN</blockquote>
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