I am not going to speculate on the quality or functionality of your ATU, however I would like to point out your measurement techniques. Understanding the fundamentals of how your radio system works is important to troubleshooting. I will try to explain some things below, and then provide a few links to other articles for further reading that may help clear things up.
When you use an antenna tuner, the antenna tuner splits your radio system into two parts: The parts before, and the parts after the antenna tuner. The part before the antenna tuner is your radio (or the output of your amplifier), and the piece of coax that connects the radio to the antenna tuner. (in the case of the FLEX 3000, 5000, this is a small piece of transmission line internal to the radio.) The part after the antenna tuner is your antenna, and the coax between your antenna and the antenna tuner. Your radio has been designed to have an output of 50 ohms, non reactive. Your feedline is 50 ohms, your antenna however, is not 50 ohms. (if it were 50 ohms, you wouldn't need your tuner) Very few antenna designs are 50 ohms. Many antennas are designed with matching networks (baluns, gamma matches, etc.) so that the input to the match is near 50 ohms at the frequency of intended operations. Most active RF devices, (in your case, the final stage of transistors in the power amplifier stage of your radio) don't like to be operated with a bad output match. (transistors rarely have a 50 ohm output impedance, so a matching network is used in the radio to transform the output impedance to 50 ohms. You then have a 50 ohm piece of coax that goes to your antenna tuner. Your antenna tuner 'tunes' until it appears to have an input impedance of 50 ohms. The SWR is measured at the INPUT of your antenna tuner, your system is happy when it measures 1:1 SWR on the input of the antenna tuner. But what about the SWR on the output of the antenna tuner? Your antenna is still not 50 ohms, its probably in the range of 10 - 1000 ohms, with a non zero complex component as well. The feed line that runs between your antenna tuner and your antenna is not the same impedance as your antenna, its probably 50 ohms if you used coax (or 75 ohms 300 ohms, 450 ohms, etc. if you use a different type of feedline here, it really doesn't matter what impedance it is, because its going to be different than your antennas impedance) What does this mean? THERE WILL ALWAYS BE A SWR HIGHER THAN 1:1 AFTER THE ANTENNA TUNER (except in the special case where the antenna impedance is equal to the transmission line impedance.) This is because the impedance mismatch between the antenna and the transmission line will reflect some of the RF energy instead of radiating it in the antenna. This reflected energy then travels in reverse down the transmission line until it gets to the antenna tuner, where it will be reflected again (this time nearly 100%) and the energy will add back to the forward power traveling along the transmission line, the process will get repeated infinitely, though the reflected components will be surpressed as they travel through the coax, as the coax will attenuate the signals the longer they have to travel back and forth on the feedline. So what does this all mean? If you are using an SWR meter AFTER your antenna tuner, you should not expect to see a SWR of 1:1, AND having an SWR that is higher than 1:1 in this part of the system is sometimes BETTER! If you do, you probably don't need your antenna tuner in the first place. Take a look at the block diagram for the FLEX-3000 : http://kc.flex-radio.com/KnowledgebaseArticle50406.aspx?Keywords=block+diagr am Notice the SWR Bridge comes BEFORE the ATU. All auto tuners will be built this way. For further reading, please examine these articles, the provide examples and thought experiments that will help you gain understanding SWR Meters Make You Stupid [ http://www.eham.net/articles/23317 ] The Real SWR Page! [ http://www.hamuniverse.com/wc7iswr.html ] The SWR Obsession [ http://www.arrl.org/tis/info/pdf/49470.pdf ] Understanding SWR by Example [ http://www.arrl.org/tis/info/pdf/q1106037.pdf ] A Mini Primer on SWR Measurements [ http://users.cwnet.com/ysarc/swr.htm ] What Does SWR Cost You [ http://www.arrl.org/tis/info/pdf/7901019.pdf ] Good luck, and I hope this helps! Greg Zenger, N2GZ -----Original Message----- From: flexradio-boun...@flex-radio.biz [mailto:flexradio-boun...@flex-radio.biz] On Behalf Of Paul Mullins Sent: Saturday, March 13, 2010 7:59 AM To: FlexRadio@flex-radio.biz Subject: [Flexradio] SWR readings whats going on I have becoming more and more concerned with displayed results. I keep getting HIGH SWR warnings on the display. So what you say press the ATU button, this happens after a FULL TUNE, the ATU setting window states at the moment SWR 1.1 forware power 11 watts reflected 0 sweet, sorry not. now tx using the TUN button or whistle in to mic, forward power 61 watts, reflected 12 watts now stick it into some thing like this http://www.ac6v.com/swrmeter.html and you get an SWR of 2.59:1 yes thats high but, hang on I just tuned that. The drop down does not indicate the swr as well. What do I do?????? I really dont know Any ideas. or is there a way of calibrating the swr pickups on the ATU board??? Just did something to prove a point dummy load on ANT 3 forward power 10 watts reflected power 3 watts swr cal of 1.6:1 on PwerSDR web page cal 3:1 on my very good dummy load (bird 100 watt unit) ATU calculation of 1.3:1 ( in the ATU settings) In bypass mode forward 50 watts reflected 1 watt web calc swr of 1.2:1 flex calc of 1.3:1 close . So does this mean I have a fault in the ATU again?. cheers sort of Paul -- Me, Myself and I accepts no liability for the content of this E-Mail, or for the consequences of any actions taken on the basis of the information provided, unless that information is subsequently confirmed in writing. Any views or opinions presented in this email are solely those of the author and do not necessarily represent those of Me, Myself and I. WARNING: Computer viruses can be transmitted via E-Mail. The recipient should check this email and any attachments for the presence of viruses. Me, Myself and I accepts no liability for any damage caused by any virus transmitted by this E-Mail. _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/ _______________________________________________ FlexRadio Systems Mailing List FlexRadio@flex-radio.biz http://mail.flex-radio.biz/mailman/listinfo/flexradio_flex-radio.biz Archives: http://www.mail-archive.com/flexradio%40flex-radio.biz/ Knowledge Base: http://kc.flex-radio.com/ Homepage: http://www.flex-radio.com/
