1.8.3 SWR Power Fold Back Too Agressive

K1ESE

I find the SWR rollback too aggressive in version 1.8.3.

Flex 6500 to KPA500 to tuner and antenna.  SWR 1.2 to one.

The Flex occasionally folds back power in the middle of a CW transmission.  Neither the tuner, Palstar HF-Auto, or amp reports high SWR.  Never had a problem with 1.7.30.

Downgraded to 1.7.30 for now.

73 de K1ESE
John

DrTeeth

I am puzzled by the introduction of this feature as I found out, when I first got the rig, it will disconnect/shut-down if the SWR and power settings are too high.

K1ESE

It would be nice if the 'feature' was either optional or adjustable. 

K1UO Larry

Indeed...  If it must be a "feature" then please make it either adjustable or optional. 

Flex_Fan

I have the same problem. I even put line isolator between radio and amp to hopefully reduce common mode but still power cutback at low SWr < 1.3. Went back to 1.7 and all OK now

[Deleted User]

So not only can some of you NOT use your Maestro because it got bricked. You can't use your amp either because of new features to protect the finals. What Next . . . Just my 2 cents here

Richard

I too have the same problem with my OM-4000A or should I say had.  I have since flushed my computer of the v1.8 and moved back to the v1.7.  All is working back to normal.  FYI... A simple "Uninstall" will NOT work so be careful.  I asked K4MT for assistance and if not for Gary I would be totally hosed.....  Been a log term Project Manager in my previous life and this release shows numerous signs of a lack of PM Leadership and Software Testing.  Flex is going to "Charge" for Upgrades in the future or something like HRD does.   Believe me this upgrade was a JOKE and things must get better in the future before they expect a pennie from this person.

WA2SQQ

Same here, I loaded the latest version and immediately noticed the reduction in power. There needs to be a way to disable this feature. Decided to go back to the older version. Like they say, if it's not broken, don't fix it!

Jon_KF2E

This is the second update in a row that I have decided to pass on. The last one did nothing to improve the operation of my Flex with SSDR. This one had one feature I would like...the ability to remotely disconnect a client but I'm not willing to **** up operation of my amplifier. 

Guess I'll wait for the next version and see...

Jon...kf2e

Gerald-K5SDR

The foldback in v1.8.3 is set to start at 25W of reflected power, which is 3:1 VSWR at 100 W.  It is based strictly on reflected power and not SWR calculation.  

Timo - OH5KW

Did you try to have some TX delay? You may transmit into open load some milliseconds, the time it takes linear relay to operate.

73, Timo OH5KW

Paul Burton

Gerald,

It appears that the foldback is being initiated by something other than reflected power.  I get total foldback  at 600 watts out on my amp, with a 1.2:1 SWR shown on the Flex 6300.  The consensus on my other thread on this subject is that it is being caused by common-mode RF (which has nothing to do with SWR).  I have put multiple ferrites on ALL lines in and out of the FLEX to no effect and I have no other overt symptoms of RF in the shack.  I'm still working on removing ground loops.  It seems that the flex is overly sensitive to common-mode RF if that is indeed the cause of the foldback.

Paul  AA6Z

WA2SQQ

Just make this "feature" user selectable

Walt - KZ1F

Paul, do you have one of those MFJ style crossed sword SWR meters where one needle is FWD the other REV and where their intersect is the point on the gradient to read SWR? This way you can measure the reflected power. I may have missed something in your discussion but I don't see how, likely the 23W FWD power, in my case to drive my KPA-500 to 600w would show up as 25W reflected. But, using that cross-sword type of SWR meter it's easy to tell. Also, you can get that program FlexMeter someone wrote and select REF power on it and see if SSDR 'thinks' it is seeing 25w REF.

Bill Roberts

I have noted the fold back issue on my 6300 when driving an ALS-600.  The SWR seen into the amplifier is typically 1.2:1.  The rig does not fold back when connected directly into the antenna, typically well under 1.5:1.  What is strange is that I notice the fold back only on CW, possibly because the fold back does not respond quickly enough ibn SSB mode?

As to ground loops, stray RF, etc.  Shack, house and lightning arrestor grounds are bonded together.  Ferrites are used generously on all cables in the shack.  My only HF antenna has a Comtek/DX Engineering line isolator installed.  There is so little stray RF, even my $7.99 computer speakers (on my Flex PC) receive no RFI.

I would vote for a quick software update to make the fold back user selectable.

73

Peter Bentley

No problems at all with 1.8.3 on my 6700.

Still will drive Expert 2k up to full output power; into a dummy load of course...!!!

G4BIM

Walt - KZ1F

Is the logic for the fold back implemented in the radio or in SSDRfM/SSDRfW?

EA4GLI

I was helping a buddy with this issue over the phone.
It was interesting that Fold Back happened when using TUNE and not when using CW side tone.
Anyone else can replicate that?

Paul Burton

Actually, I have the opposite.  If I use the TUNE option to tune the amp at low power and then increase the TUNE power to max, I get NO foldback.  If I then click the TUNE option OFF and then back ON it folds back.  Or if I go to normal keying after tuning up, it folds back.  So the question for me is why does  it NOT fold back when the tune power Is advanced from a low setting to max.

Paul

KY6LA_Howard

Paul

You need to take a look at the reflected power at your radio

Here is a link to a program called Flexmeter  https://db.tt/A9TEtwQK 

You should be able to read what your radio sees internally as reflected power with the Flexmeter

Alternative.. if may be that your TX delay may need to be changed as the relays on the tube AMP may be so slow that you are seeing an open circuit on initial transmit.

Paul Burton

OK, thanks.  I definitely appreciate your suggestions and expertise in this.  I did as you said and found that the peak reflected power on key-down shows at about 70 watts even though the SWR shows as 1.3:1.  So that seems to be causing the fold back.  Adding TX delay had no effect on these readings or the fold back. 

The interesting thing is if I start in TUNE mode at minimum power level and then increase the power slider to max, the reflected power stays below 2 watts and I get no fold back at max power.  But if I click on TUNE while it is at max position, it immediately folds way back.  Then if I leave it in the folded back state for about 10 seconds, it the reflected power goes down and the fold back goes away.  It's a temporary fold back for about the first 10 seconds of every transmission.

I was buying into the common-mode RF interaction theory for a while, but with this weird behavior I'm not so sure.  I'm still working on better grounding.

thanks,  Paul  AA6Z

WA2SQQ

Just checked out the meter reading software - it's very simple, and twice as useful! That's nice tool to have. Thanks for the tip!

Al_NN4ZZ

Paul, A while back I had some issues with common mode RF getting back to the radio. One of the symptoms was erratic swr readings ( and assume the reflected power readings would be erratic as well). Perhaps that is what is triggering the foldback. It would be interesting to hook up an external swr/reflected power meter at the radio and see if the readings match what the radio reports via the Flexmeter app. For reference here is a link to my web page with info on the rf problem and my solution. http://nn4zz.com/FLEX6700.htm#RF_issues_and_solutions Good luck and let us know what you find. Regards, Al / NN4ZZ

Walt - KZ1F

That was my point Al, I'd take Gerald's word the radio thought it saw 25w. My suggestion was to see what it, in fact, was.

Al_NN4ZZ

Hi Walt, Agree, I didn't want to jump to any conclusions but if the swr bridge / sensing circuit is being negatively affected by the common mode RF then it could erroneously trigger the foldback. Paul reported a reading of 70w of reflected power which seems unlikely at an swr of 1.3. I definetly observed erratic swr readings on my 6700 before I corrected the common mode problems. Someone that is experiencing the problem and can compare the. Reflected power reported by the radio ( i.e. Flexmeter app) as well as an independant external meter might provide some good data for FRs to consider. FRS may already be setting up some mismatch scenarios in the lab to see if they can duplicate the issue. Regards, Al / NN4ZZ

km9r.mike

Larry - WA7LZO

If the only parameter "looked at" in v1.8.3 for fold back is 25 watts of reflected power, irregardless of forward power, then I'm confused. While 25 watts of reflected power is an SWR of 3:1, given 100 watts of forward power, with an Alpha 9500 running 1500 heart hammering watts of forward power, a reflected power of 25 watts is an SWR of 1.3:1. So, what gives with only looking at reflected power? That algo goes out the window for the ham running a linear amp. As Bill O'Reilly might say, where am I going wrong here? 73, Larry

John-K3MA

I think you are confusing the reflected power that the Flex will see versus what the amplifier will see.

Walt - KZ1F

I have a solid state amp that looks to the radio as 1:1. I set the internal atu to bypass. My hypothesis was that wasn't unique to solid state otherwise wouldn't one need a tuner just to match to their amps input? However if this is unique to mfj amps.....

K2CB Eric Dobrowansky

Your radio is looking at the input impedance of the tube, not the antenna, when the amp is in operate. 

A possible issue is that the input of a tube amp can sometimes have a flywheel effect, and depending on the phase of the rf input signal, the input impedance can vary, especially on SSB, from syllable to syllable.  For example, if I watch the LP-100A on the input of my Alpha 9500A triode tube amp, the swr will vary during SSB transmissions, but on a solid carrier, the swr remains stable. Meanwhile, the second LP-100A on the output side of the amp shows the antenna SWR as stable and consistent, whether in carrier mode or ssb mode.

On the other hand, with my tetrode based amp that uses a 50ohm resistive input circuit, it is not as noticeable. 

See this very informative page by Tom Rauch W8JI.  http://www.w8ji.com/tuned_input_circuit.htm

I suspect the VSWR bridge in the Flex may be more susceptible to this scenario than the typical transceiver.  If you search the archives, you will see that in the past, others have reported similar "falsely high" swr readings on the internal Flex SWR meter, as compared to their external SWR meters. For those with the issue, it has probably been occurring since day one, but now that the latest software release has fold back enabled, those users are just now becoming aware of it.

I've seen similar results on the ANAN transceivers as well. The fix was to disable the SWR protection in OpenHPSDR when using an amp or antenna tuner.

Hopefully Flex can give us an enable/disable option in the next release.

Eric

K2CB

K2CB Eric Dobrowansky

The other issue is that with automatic tuners, they need a steady drive level to tune properly.

With the power fold back enabled, as the tuner changes the impedance, the radio's fold back algorithm tries to compensate for the load variation by varying the ouput level. Then the tuner tries to compensate for the new/different measurement based on the new drive level, not realizing it is due to a power level change during the tune process,  in a never ending loop.  

Preprogram your automatic tuner presets for the frequencies you regularly operate on, THEN enable the fold back protection.  If something changes out of the ordinary, the protection will be there. (if and when we have that option, thus the need for it).