Quivering SSDR power level

Pat N6PAT

This morning I turned on my 6700 and tuned 160 meters. I always have the power level on 160 set to 2 watts which feeds my RM Italy HLA 305V 250 watt amp. Just 2 watts into the amp on 160 gives me full power.

A few minutes after tuning up while making a CQ call in FT8 I saw the power level in SSDR quivering and exceeding the band specified 2 watts limit peaking at about 4 watts. The overall maximum power for the radio is set to 9 watts but for 160 it's set to 2 watts in the TX band matrix. This jumping in power from my 6700 was causing variations in output power from my amp as measured by my LDG Pro 600 tuner so I have ruled out a false power reading in SSDR.

I immediately shut down the amp as the unstable 6700 power output was now causing the amp to exceed the rated power and I didn't want the amp damaged.

I tuned 160 again and this time the power stabilized at the specified level. I checked other bands and saw no issues. I used the radio a few more times today on other bands and did not witness the issue again. I also tuned up on 160 a few more times and all was well.

This latest issue is very concerning as the power output should never exceed the maximum specified for the band. The timing is also very concerning as I just had the 6700 finals replaced and now I'm wondering if this issue is what fried the finals in the first place.

This is yet another power output related issue. Not long ago I posted about the TX output dropping to zero several times.

My power supply is locked to 13.8v and is functioning normally as indicated by DDUtil and FRStack test measurements I did for Tim when the finals failed in November. 

I should point out that after the problem disappeared I checked the TX
band matrix and the power level for 160 was still specified as 2 watts even though that was exceeded when the issue occurred.

This radio continues to excel in providing 20+ in aggravation and has put a damper on my enjoyment of this hobby as I never know what to expect when I turn it on.

Pat N6PAT

It did it again this morning. Next time I'll try to capture it on video.

Dan-N7HQ

Hi Pat,

You are using an external power amplifier designed for use with a much lower power transmitter, 10dB less per the HLA-305V spec. Connecting a 100W-capable transmitter to the input of an amplifier with 13.5dB gain, designed for <=10W of drive power, is similar conceptually to connecting a line-level audio signal directly to a microphone-level input and turning the volume down to 2.  

In your use case, though impedances probably match, the level mismatch creates a situation where power level control is far-too-sensitive and the results potentially problematic. If a more-precise control using this configuration is essential to you, then insert a 50-ohm 10dB attenuator between the 6700 and your amplifier. Make sure the attenuator is capable of dissipating 100W. That would allow you to adjust output power from between 0 and 250W, at approximately 2.5W per ordinal value on the level control. A value of 2 on the control would result in approximately 5W of output, a value of 50, 125 Watts, and so forth. 

A common misconception is the power slider, and TX Band Settings values in SmartSDR correlate to power in Watts. They don't. They are relative power levels, and if you look, there are no labels that indicate Watts in the UI for that reason. It's true, for barefoot and exciter use cases, the correlation is close enough, but that's because all FlexRadio transceivers have 100W PAs, and the scale of the level control is from 0-100. There is more involved in the actual transmit power than the level control. The temperature of the PA transistors is one factor. When transistors are cold, our amplifier produces slightly higher output for a given drive level than when they are warm. This is why when you first transmit (using a cold PA), you generally see more than 100W and less power output when the PA is hot.  

We calibrate FlexRadio power amplifier output and meters using an external Mini-Circuits PWR-4GHS precision sensor after warming the PA temperature to 45C. Amplifier measurements at a number of drive levels are stored in EEPROM, and those values are used in a curve-fitting algorithm to manage and display relative output power. 

To find actual transmitted power in Watts from your 6700 (and the power meter doesn't support the resolution you need), employ a calibrated external Wattmeter between your amplifier and 6700. 

73,

Dan

Pat N6PAT

As I said in my comment the sudden fluctuation of the power level in SSDR is confirmed by the LDG watt meter.  Each time it quivers so does the watt meter regardless if the amp is on or off.  This is an actual fluctuation of the output power and not merely an issue with what the power slider is displaying.

I maintain the power level at 2 watts and normally it is rock solid as I would expect it to be. This new behavior is intermittent and unpredictable.

Another thing to consider is that when the level jumps it is exceeding the power level stated in the TX band matrix. That is very bad.

Given the recent blown finals I am now concerned about a repeat performance. I am now wondering if this power instability was somehow related to the failure of the finals.

I will attempt to capture this issue on video if/when it happens again.

As I've stated all along this radio has serious problems. After all, even Gerald could not , and never did,   find the cause of the SWR Bridge issue back in May.

Pat N6PAT

One other thing to consider: I and others have reported issues with power loss while attempting to transmit. I'll be making QSO's when all of a sudden the power output drops to zero. I'm now wondering if that power issue is somehow related to my current issue

If you check this forum you'll see several posts about this problem.

Pat N6PAT

Dan,

Well my worst fears have come true. I turned on the 6700 this morning and tuned to 160. I turned on the amp and started to transmit. The power slider in SSDR started to quiver and before i knew it the RM Italy HLA 305V amp died.

This is the second time this has happened. When the 6700 finals blew in November it took the amp with it. It took 3 months for the amp to be fixed by DX Engineering and now it's gone again. Feel free to confirm this with DX Engineering.

In anticipation of your questions:

1) This is not an SWR issue as both the SWR readings in SSDR and the LDG meters ( both digital and analog) read low SWR. The onboard ATU tunes up without any issues as well.

Also, the amp has SWR protection that will shut down the amp and sound an alarm if the SWR exceeds 3.0 . The alarm was not tripped and the amp did not shut down.

2) This is not a power spike issue as the 6700 and the amp are on separate power supplies powered by separate power circuits. Both power supplies continue to operate normally. The power to the 6700 is correct as verified by DDUtil and FRStack

3) This is not an antenna issue as I was getting good reports on all bands. I've included a screen print of recent contacts confirmed in LOTW  as proof. (see below - Afghanistan, China, Kuwait, New Zealand, etc.)

4) This is not a coax issue as I am using expensive LMR400 Ultra Flex and all connections are secure. I double checked

5) This is not an operator error as I've been operating this radio for 3 years and had no serious problems until the XO started to malfunction last spring. Then I was told by FRS about the mysterious problem that could not be diagnosed. That when all the problems began.

So now I have a $7,000 radio that I'm almost afraid to power up as I can no longer trust that it will function correctly.  I am also out a $700 amp.

Pat N6PAT

I did some additional checking and I have found the problem with the amp and it is NOT what I had thought and stated before.

The actual problem is that in the TX band matrix the TX1 check box for 160 somehow became unchecked. I rarely change any of those values as I have no reason to but this caused the amp to not key on 160. How this box became unchecked is unclear but I know I did not uncheck it. It was working when I shut the radio down last night and was not working when I powered it up this morning. I have no idea what would have caused that TX1 box  to become unchecked.  Only that particular box because unchecked. All the others remained checked.

So I wanted to state that I can now get power from the amp again but this still does not address the quivering of the power slider.

I was wrong about the the amp failing on 160 and when I'm wrong I admit it.

Doug Hall

Pat,
I experience the phantom "TX1 unchecked" from time to time with my 6300. While I have no proof of this I believe that it is due to some setting in DDUtil. I am running SSDR 2.6.0 and DDUtil v4. I don't recall seeing this with v3.
73,
Doug K4DSP

Pat N6PAT

You may be right. I don't have any reason to change those settings from the initial setup so it did not occur to me that that could be the cause.

I don't normally run DDUtil but I did to see if I could determine what was causing the power fluctuations. That , in turn, may have switched off the TX1 box. Thanks for the info. I'll keep an eye on it.

Now I still have to be concerned about the power level

Doug Hall

I've seen the quivering power level before too, but it was only when running FT8, and even then it happened very infrequently, so this was likely a different issue from what you are experiencing. I only saw the problem with my notebook computer. In that case I determined that the audio level into DAX itself appeared to vary which, in turn, made the output power vary. Didn't happen on any non-digital modes. I have never seen this on my hamshack computer.
73,
Doug

Pat N6PAT

I was also running FT8 when this happened. I've been using FT8 on this radio for about 2 years on all the bands from 160 to 10 and normally there are no problems with the power level. All the problems began when the XO failed and it went in for repair.