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TX power spikes

When transmitting on SSB, I see regular power output spikes well in excess of the RF power level setting.

For example, I set the RF Power slider to a value of 45.  I also set the TUNE slider to a value of 45.  If I press the TUNE button, I measure a carrier power of approx. 45w.  Likewise, if I produce a steady tone into the microphone, I also measure a steady power of approx. 45w.  

When talking into the microphone, obviously my average talk power will be down some, but in addition to seeing the normal peaks of approx. 45w, give or take, I am regularly seeing SPIKES of power upwards of 60-70w.  Maybe every 20 words or so, I will see the spike in transmitted power. 

If I set the RF Power slider to another value, I still see spikes in excess of the desired level setting, whether it is set for 25w or 75w. The spikes appear to be approx. 40% higher than the set level. For example, if I am set for 25w, I will see spikes to 35w. If I am set for 70w, I will see spikes close to 100w.

I am measuring this on two LP-100A meters. One coupled to the input of my amplifier, and one coupled to the output.    While watching both meters, I normally see 40w into the amp for 1500w output. However, when I see the spikes, the input will hit peaks of 60-70w, and correspondingly the amplifier will spike to 2000w or so.   Not good for expensive tubes, nor remaining within legal limits.

When I initially called Flex to reported the issue, it was recommended to try running the compressor. I have tried operating with the compressor enabled, which has made no difference in the issue.  My mic gain and audio input levels are adjusted so that my extreme voice peaks are just reaching the 0DBM point, and average voice levels are at the "L" of the word LEVEL.

The issue is occurring on all bands. 80,40,20,15m tested so far. It occurs regardless of whether the TX equalizer is enabled or disabled. Likewise, I can enable or disable my external audio processor (Symetrix 628), with the same results.

This appears to be quite similar to the old ALC issue that plagued the 5000 for a long time until the corrections were made in PowerSDR.




  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2017
    I have converted this topic to a support HelpDesk ticket (http://helpdesk.flexradio.com) for expedited issue resolution.  If anyone else is experiencing an issue similar to this one, please submit a HelpDesk support ticket for issue resolution.
  • K2CB Eric Dobrowansky
    K2CB Eric Dobrowansky Member ✭✭
    edited November 2018

    I am still seeing the power spikes even after upgrading to the latest V1.2.1.  And a second Flex 6500, no less.



  • Dale KB5VE
    Dale KB5VE Member ✭✭
    edited January 2017
    I have followed this thread and having experienced the issue in powersdr I have seen it happen and corrected by Flex. After seeing what was said I did some checks on my equipment. I am running the 6500 and Alpha 8410 with the wave node meter system monitoring the output of the alpha and a second sensor on the output of the flex. I can monitor both side by side on my screen. I run the power slider at 20 ( settings do not always equal true power out) and this will give me a tune power out of 1500 wats with the tune set at 20 also. At this point all is great. Let me take time to tell what my audio system is, I run the pr 40 mic and a Art tube mic preamp and have no 20db boost on and a mic gain of 21 with the processor on in dx1, I do induce some tube amplification and a 75 hertz cut off along with a little compression keeps the audio rich without a lot of base effect and also keeps the average signal very strong without splattering . Saying this I noticed tuned output with rf set at 21 I would get about 17 watts out on my 6500 and 1492 watts out of the alpha. When I ran a test on the modulated output to hit some peaks of 20 watts from the radio and 1621 watts from the amplifier. At that point I adjusted the Ssb rf slider to what was necessary to keep my output from going over 1500watts. When doing this I ended up with the slider at 17 on Ssb and my average peak power is 1385 watts out (as most of y ou know in reality if my signal was checked by a oscilloscope I probably was over true 1500 watts pep) so I then hooked up my bird 43 with the bird peak reading board and confirmed what I was seeing on the wavenode. So on my unit i am not seeing a spike but the results of the Ssb modulated signal is about 15 % more than the rf tuned signal. I do not see a spike like the icom 706 and many other radios give off. My amp faults at 61 watts and it is very fast to do that. It boils down to the days with the old tube final transmitters we would peak out the transmitter using the tune position or the cw position on some rigs and then your peak Ssb modulated signal would exceed the cw carrier if you had a scope or a good peak meter. After all this my question to flex is what class is the tuned position and is the Ssb signal set to be greater pep power than the tuned output. I have set my set up as described above with no problems.
  • Sergey R5AU
    Sergey R5AU Member ✭✭
    edited April 2017
    Yes, i have the same as described, on F6700 with 100% output  on peek visible  over 120watts
    I would like aslo notice what full ALC (-4v) do not limit output power, with -4v and 100% level of the power - output nearly 90-100watts 
  • K2CB Eric Dobrowansky
    K2CB Eric Dobrowansky Member ✭✭
    edited November 2018

    I have a nearby Flex 6500 owner who reports he does not see spikes. However, he only runs his radio at around 20w to drive his amplifier to legal limit.  So I made some tests, and it appears that if I set the radio for 20w or so, the spike is much less pronounced, almost not detectable unless you really watch for it, and then it is only a few watts over the set power level.  It appears that the higher the power level is set for, the more pronounced the overshoot is. As Sergey discovered, if I also run my power control to 100w, I also see spikes upwards of 120w at times.

    I normally run 45w to drive my amp to 1500w, and periodically notice spikes to 60w, obviously resulting in my amplifier spiking to 2000w.  Fortunately the amp had the headroom to handle it, but never the less it is not a good thing.......

    Unless you have a fast responding peak meter, such as the LP-100A, you may never even see it happen.



  • Roger Miller
    Roger Miller Member ✭✭

    I have the same problem with my 6400 and solid state amp. The spikes cause my amp to shut down constantly.

  • Iu4jnr
    Iu4jnr Member ✭✭
    edited February 26
    Hi all,
    I have the same issue. Keeping the microphone levels as per manual, i occasionally have a power overshoot, beyond the power set in tx band settings. In two occasions I had my PA (Acom 600S) warned me about power too high. :o :/
  • John KB4DU
    John KB4DU Member ✭✭✭✭

    Is there any boost frequencies in the TX eq? The eq is after the level meters, so there may be more output than expected.

  • Iu4jnr
    Iu4jnr Member ✭✭
    > @"John KB4DU" said:
    > Is there any boost frequencies in the TX eq? The eq is after the level meters, so there may be more output than expected.

    I tried several mic profile and I have the same behaviour. I also turned off the TX-eq and occasionally the pwr overshoot. This apparently happen only in SSB, in CW which I use most i didn't noticed any.
  • rdwing
    rdwing Member ✭✭

    Is there any conclusion to this? I regularly see 140w peak on my 6400 with sideband. I am just using headset connected to the PC, and sent to the flex via PC audio.

    The meter is a wavenode WN-2d which has very fast peak power reading capabilities, and I have confirmed this behavior with another Flex 6400 owner.

  • Iu4jnr
    Iu4jnr Member ✭✭

    I changed to a Radio connected microphone, played with mic gain, power setting and Equalizer and now audio peaks are in the range not to overshoots my SSPA. The mic I'm using is a Sennheiser GSP500 headset.

    Overshooting was happening mostly with a PC studio microphone.

    I wish there will be a better limiter in the future.

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    If you are seeing spikes, then you need to open a support ticket.

    We do extensive testing and spikes are just something that do not happen. If you have a valid way to measure them and capture them on a dummy and trust your test equipment, then our service team wants to see your radio. They will want you to send it in.

    A video will be very helpful showing the wavenode readings and also the Mic Level Meter at the same time.

  • Dan Trainor
    Dan Trainor Member ✭✭✭

    I have RF power spikes on my 6400. I use USB microphone on MacBook and Windows. The External audio processing software has a hard limiter in line upstream of flex audio input. I measure no spikes in audio fed to Flex. Yet, RF spikes occur every X (random) secs to high levels. I will send 6400 back for repairs once I get my 6600 back from repairs. Hopefully there is a remedy.

  • Dan Trainor
    Dan Trainor Member ✭✭✭

    I have received my Telepost LP-500 Power / SWR / Modulation monitor.and it's all set up. This is.an ultra fast and accurate test instrument. Proving to be an excellent diagnostic tool. On AM mode, I am observing RF spikes on the RF waveform display and also the AM modulation monitor is reading >150% Positive modulation due to the RF spikes. (This test instrument is fast enough to catch them and I can see them visually in the waveform screen). My goal is to achieve about 120% Positive modulation (which is ideal), but I can't get there with these spikes occurring. To note, this is not an audio issue as no spikes are occurring in audio chain. So, I have confirmed the presence of these RF spikes (objective evidence) and will open a ticket. I suspect this is a bug in the 6400 hardware/firmware. I just need to takes videos of same and send to flex in the context of a help ticket. if anyone else.is seeing this issue, it would be useful to know for additional confirmation. Thank You, dan de WA1QZX

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