40M SWR too high

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  • Updated 3 years ago
My ATU tunes every band except 40m. My IC-706 reports 1:1 on 40 with no tuner, but transmitting with the flex reports a high SWR with either Bypass or ATU on the same G5RV and the ATU fails to tune only on 40M.

The ATU reports successful on ALL other bands (well I haven't tried 160M).
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Robert -- N5IKD, Elmer

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Posted 5 years ago

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K2CM

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I have found that my SWR reading is accurate on all bands....agrees with the SWR reading on my PalStar tuner.

I do, however, have RF feedback on some bands that totally messes up my F6.7K and computer, even at low power. It is possible that RF feedback is causing your problem.

I have installed RF ferrite cores on connecting cables to reduce my problems. You might want to reduce your power on 40mtrs to see if that affects your readings. If so, then you will have to solve the RF feedback issue.
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Robert -- N5IKD, Elmer

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I have ferrite cores on anything that is not coax, and tried transmitting at 10W.

I can just move the coax between the 67K and the 706 and I have no problems with the 706 at 100W.
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Tim - W4TME, Customer Experience Manager

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if you have an unbalanced antenna, you may need a good commom mode choke on the coax.
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Robert -- N5IKD, Elmer

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The antenna is a G5RV. It works on all bands with the 706 and all bands but 40 on the 6700.
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Sergey, R5AU

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Hi Robert, i can report a vise verse with ATU on 40m, i have one ANT which never can be tuned in any situation by ATU of my IC-7600, but F6700 do it sucessfully. You know very important the class of the reactance and gradient of reactance on dedicated freq, this is always has impact on tuning process. Have you the same problem with any other radio or ?
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Robert -- N5IKD, Elmer

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The 706 and 67K are the only HF radios that I have. The other bands tune fine.

The MFJ antenna analyzer reports good SWR on 40M.
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Sergey, R5AU

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Robert, you know g5rv a bit interesting antenna from tuning perspective, how long you symmetrical line( I think you av classic one 600ohm) and coax after transformer
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Robert -- N5IKD, Elmer

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I don't remember the exact dimensions, but it is coax from the back to the radio with about 18 inches if ferrite cores as a choke at the antenna end, followed by about 34 feet of ladder then about 51 feet of wire in each direction (for a total antenna length of 102 feet)

Why does this work for one radio on all bands and on the other radio on all bands except 40?

I will put an external SWR meter on it and compare the signals from the two radios.
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Sergey, R5AU

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Well, Robert, you know SWR meter unfortunately did't show gradient of the reactance, even SWR=1,5 can be show with meter but in reality it will be different as Rant= R+jX. In you case you can check with add 4-7 feet of the coax to you 18 inches additionally.
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Robert -- N5IKD, Elmer

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Here is the antenna analyzer result for my G5RV across 80-20 meters. The G5RV will not tune anywhere on 40 meters.


And the antenna analyzer result for my 40 meter loop.


and here is the 40 meter loop across 40 meters only. The ATU will tune the 40 meter loop on several bands, but only between 7.120 and 7.185 on 40 meters.


With a dummy load the ATU will tune on any frequency including 40 meters. with two dummy loads on a T-connector the ATU will tune anywhere except 40 meters.
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Paul Christensen, W9AC, Elmer

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Is this a Z sweep at the line input (i.e., what the Flex sees)? In both cases, the tuner should be able to attain a match with ease on 40m. On your G5RV at 7 MHz, the Z is 100-j50. On the loop, it is 25+j5. The latter is a bit low for some tuners, but should still be an easy match for a typical stepped-relay tuner.

As Sergey suggested, change the coaxial line length, perhaps in increments of several feet until you find a combination that works.

While on a recent camping trip, I ran into this issue with my Johnson Matchbox. Rig was an Elecraft KX3. 80m dipole for all-band operation, fed with real 600-ohm balanced feeders. Initially, I could not get a match on 40m. Adding a few feet of 600-ohm line solved the problem as that resulted in a change in the Z seen at the line input as it changed just enough within the limits of the Matchbox. The SWR on a nearly loss-less line remains constant but when there's an antenna-to-line mismatch, changing line length greatly affects line input Z even though line SWR is not changing.

With all of the above said, I'm really surprised the Flex will not match into those two complex Z values. I would not rule out some other anomaly like coaxial common-mode current that may be affecting the Flex's phase detectors.

Paul, W9AC
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Robert -- N5IKD, Elmer

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Paul,
I can try changing the length of coax for the G5RV and 40 meter loop, but I am having issues with just dummy loads.

When I Tee two dummy loads together, the ATU will tune on all bands except 40 meters. The T is located on the back of the radio and I have a 3ft coax to each dummy load. It should at least do this regardless of the performance of my antennas.
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Paul Christensen, W9AC, Elmer

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I deliberately mis-tuned my homebrew balanced tuner and tried several wildly high and low Z values on 40m with my Flex 6700. In each case, it found a match below 1.5:1. I also tried this test on various parts of 40m. I'm not implying anything except to note what I'm seeing here.

Paul, W9AC
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Robert -- N5IKD, Elmer

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Paul,
Do you have two dummy loads that you can attach using a Tee to see if it will tune? I am thinking that there is something wrong with my radio. If yours won't do that then maybe it is just my antenna or length of coax.

It sounds like from your description that my G5RV and 40 meter loop should both tune on 40 meters just fine.
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Ernest - W4EG

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Robert,
I tried to duplicate your problem and I was not able to notice your results.
I'm using a Hy-Gain 18-HT (vertical 160-6m) and a 160-6m OCFD full length (210'+90' legs) and the antenna tuner performs flawless. The SWR was not higher than 1.7 for (most) of the entire spectrum. The worse I saw was on 6m with a 2.5. However, I worked stations up and down the pacific coast.
I also used a Bird Thruline and it was flat.
The F6.7K internal antenna turner is far better than the one on the F3K & F5K; quieter and faster too.
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Robert -- N5IKD, Elmer

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Thank you Earnest.

I agree that I am able to tune everywhere that I expect to be able to tune and more, with the unfortunate exception of 40 meters.

Do you have two dummy loads that you can Tee to simulate 2:1 mismatch? When I try this I can tune everywhere except 40 meters. I think that this take my antennas out of the equation, but I would like to see if others have the same results.

Since you were able to tune the 2.5:1 on 6m, I think that my antennas should be able to tune either of my antennas across the 40 meter band. And it should absolutely be able to tune the two dummy loads in on a Tee.
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Ernest - W4EG

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I will try to T; using low power (20w) dummy's and see what happens.
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Robert -- N5IKD, Elmer

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If I leave my Flex 6700 in bypass and use an MFJ tuner then the MFJ tuner will tune anywhere on 40 meters on the 40 meter loop, but the SWR indicator on the Flex still indicates high.

The 40 meter loop tunes fine on 20 meters and 10 meters with the Flex ATU by itself or with the Flex in bypass and using the MFJ. In this case the SWR meter on the Flex reads fine.
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Paul Christensen, W9AC, Elmer

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Robert,

When the MFJ tuner is optimized, its Z at the input will be 50+j0. We all know that as we routinely adjust our external tuners for minimum SWR between the tuner and transmitter.

So, if you are achieving a match with the MFJ tuner with the 6700 tuner in bypass -- and if the 6700 SWR indicator reads high only on 40m after a match with the MFJ, that tells me perhaps a relay, circuit trace, or component specific to the 40m transmit path is the culprit in the 6700. I'm not sure if any of us have access to the Flex 6700 schematics, but an area of interest would be the 40m LPF. It's probably time to call Flex and open up a trouble ticket.

Unfortunately, I only have one Bird TermaLine load and cannot parallel two without another load.

Paul, W9AC
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Robert -- N5IKD, Elmer

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I opened a trouble ticket two weeks ago. Troubleshooting through the trouble ticket is very slow due to delays on my part in obtaining equipment for troubleshooting and my inability to convey the seriousness of this situation to FlexRadio.
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W5XZ - dan

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Robert, could it be your ant + feedline length is just 'diabolical' to the flex tuner on 40m? i'd try adding about 1/4 Lambda more coax in the shack, if it's cheap and easy.

JM2C. Merry Christmas, 73, W5XZ, dan
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Robert -- N5IKD, Elmer

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I can try that, but that does not explain:
1. Why does the ATU fail to tune two dummy loads in a TEE configuration only on 40 meters? (no antenna involved)
2. Why does the FlexRadio in bypass show high SWR into the MFJ tuner only on 40 meters, but shows fine on all other bands?

I will try changing the length of my coax, but I am concerned that this is distracting from the actual problem that the radio has a problem.
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W5XZ - dan

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reminds me of what Neil Sperry told a lawnmower owner once: "m'am, I think
you have the mower from Hell...."
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Robert -- N5IKD, Elmer

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HI HI
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Terry - W4TRH

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Robert,
I just bought my 1st SDR radio from Flex (6300) and I am having the same issue you describe.  I am using a Carolina Windom and had a ICOM 706MK2G which had no issue tuning the antenna.  The MFJ shows the SWR at 2.5 on the low end and 2.9 on the high end.  All other bands from 6M to 160M tune with no issue, even when having a higher SWR of 3.1+.  Can you tell me what you found to be able to tune the Flex on 40M?  Thanks Terry
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Robert -- N5IKD, Elmer

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Terry,

I set up a help ticket and the FlexRadio staff determined that my radio required calibration. They paid to have it shipped back to Austin, calibrated it and promptly returned it.

I have not had this issue again.

Robert
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Terry - W4TRH

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Robert,
Thanks for the information.  A little bummed since I just got the radio from Flex a week ago on their ceritified preowned program.
Thanks Again
Terry
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Lee, Elmer

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A Carolina Windom is an OCF antenna and is even worse when it comes to ground loops and RF in the shack than a G5RV because it's inherently unbalanced besides being mismatched.  I had one of those as well, as well as one of Carolina's super loops that supposed turns into a bi-square which also is a RF nightmare.  The W5GI works fine 160-6 as long as I maintain it.  
73  W9OY  
(Edited)
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Tim - W4TME, Customer Experience Manager

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Terry's issue was resolved via the Helpdesk by resetting the ATU memories
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Robert -- N5IKD, Elmer

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Great! Helpdesk to the rescue once again.
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Lee, Elmer

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Antennas like G5RV's and Carolina Windom's have inherent RF issues.  I've used them both and have seen an instability issue with increasing power often on 40M.  The G5RV's problem is mismatch and going from balanced to unbalanced, and the Carolina Windom's problem is it is inherently unbalanced from top to bottom with mismatch as well.  This causes common mode current on the feedline which then causes common mode current on the radio, often called "RF in the shack".  Effectively the radio is attempting to become part of the antenna.  Common mode current tries to somehow return to the ground side of the transmitter any way it can and cause a LOT of problems.  

In my case I've run both Carolina Windom's and G5RV variants with variable success.  A Carolina Windom will never solve it's common mode problem because it's inherently unbalanced by design, despite the hype.  A G5RV is balanced but mismatched and becomes unbalanced when the twinlead becomes coax.  You can try chokes and baluns or UNUN's with varying success.  I never was able to satisfactorily solve the Carolina Windom common mode problem so I discarded it.  Multiband is not worth RF everywhere.  The G5RV for me needs a long feed line and some of that feedline formed into a coil a coil somewhere in the length.  Even so these antennas are a setup to arc especially at coax connector spots (where 2 pieces of coax join to each other) and especially if you try exuberant use of chokes which causes high impedance and the likely hood of an arc to soar.  I've found these antennas require maintenance to replace and repair arcs.  

http://www.w8ji.com/common_mode_current.htm

http://www.w8ji.com/windom_off_center_fed.htm

http://www.w8ji.com/g5rv_facts.htm

73 W9OY