Flex 3000 SWR question.

Greg

A very good friend of mine has a 3000. On 80M with the tuner bypassed the radio shows an SWR of 1.2. But if he diconnects the coax and connects it to an AA-54 analyzer it shows and SWR of 3.2 on the same frequency. On 40M the radio shows something like 8 to 1 but the analyzer shows1.6 (or something close to that...going by memory). Both checks were done with the tuner bypassed. I don't know if bypass is really completely bypassed and there could be some differences due to some stray capacitance but there should not be that much of a difference. He is considering doing the calibration process but the KB article on that is apparently (according to him) very outdated. Any ideas for him? Tnx Greg

Tim - W4TME

Does the ATU find a match regardless of what the radio is reporting as the VSWR? And if it does find a match is the PA putting out full power? If both are "yes" then I do not think there is an operational problem with the radio. If "no", then I think there may be something going on with the SWR bridge and I would recommend that the radio be sent to Austin for a recalibration and test. To do that, a HelpDesk support ticket needs to be entered so we can triage the problem. (http://helpdesk.flexradio.com)

Greg

Thanks Tim. I think the radio was just recently back for something else. Don't the recalibrate as a matter of practice anytime a rig is worked on? I passed this all to Steve and he will either email you direct or set up an account here. 73 Greg

Tim - W4TME

Yes, we recalibrate every radio that come in for service. I think we need to deal with your friend directly. Please have him submit a HelpDesk ticket so we can investigate further.

Scott AC8DE

This can be complex to find the problem, if nothing is wrong with the equipment. I experienced things similar to your friend with Flex's and other rigs and there was nothing wrong with any of the equipment. The most common culprit is common mode issues. The second is a bad ground path. The 3000 I assume is grounded and the analyzer is not. I've had an analyzer hooked up and it gave different readings whether I was holding it in my hands or had it laying on the desk. (Capacitive effect with my body) Lack of a common mode choke at the shack entrance, potentially resonant feed line lengths, current node is EXACTLY the wrong place, loose ground, bad solder on ground side of connector, etc. So before we blame the rig, all this needs to be gone through. And don't forget to check SWR at very low and high power levels. If it changes, then it us most likely a bad ground path or common mode issues. And don't forget to check adding and subtracting some extra feed line to see if the extra feed line length makes a difference. Also try moving the Flex tuning 10-20 Kc and compare the tune with the analyzer again. If the difference between the analyzer and Flex are now closer or farther apart, you could have a current/voltage node issue and need to change feedline lengths. And of course check it with a third device; a second rig or another brand of analyzer. If two readings agree, then the third device is suspect. If none agree, then I suspect there is something going on with the station set-up. How far is the antenna away from the shack and what kind of an antenna is it? Wouldn't happen to be a radial-less vertical would it? Scott AC8DE

Dudley-WA5QPZ

And to add to Tim, the SWR is calibrated by presenting a 25 ohm load to the radio ( two known good dummy loads "T" together) which yields a SWR of 2:1 , checked in the middle of each band. Your friend can verify the SWR readings... But also 40 meters has always been a problem for me with RFI, particularly common mode RF, coming back down the feedline into the shack, this can effect the computer and the radio which can effect the readings coming from the radio to the computer.. If your friend continues to have problems , have him open a Support Ticket on the Help Desk..

Greg

Thanks folks...I will pass this on to him. Looking forward to the 6700 arriving home today. 73 Greg