RF overshoot

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  • Updated 3 years ago
RF overshoot
Photo of K2CB Eric Dobrowansky

K2CB Eric Dobrowansky

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  • frustrated

Posted 3 years ago

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David

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Can you provide more details?
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K2CB Eric Dobrowansky

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For some reason my text never posted. Let's try again..........

I just switched back to using my Flex-6500 after using other radios the past few months. I have updated to the latest release.

I am surprised to see that severe overshoot still exists. If I run without the compressor, the output power seems to be ok for the most part. Maybe a slight spike every once a while. However, if I use the compressor in the normal mode I see severe overshoot. Every transmission. Maybe once every few words.

For example, if I set my RF output for 45w in order to drive my 8877 to 1500w pep, I regularly see spikes upwards of 70w. This results in the amp being driver to over 2k. Not good.

I am monitoring my power output with two LP-100A meters. One monitoring the input drive power, and one monitoring the amplifier output power. The spikes track identically on both meters. When the exciter power spikes, I see the resulting amplifier output power spike at the same time.

I reported this issue early on well over a year ago. At that time, I was asked to try different microphones and different audio inputs. I reported back that the audio input location did not seem to matter.

I never did hear anything back on the matter. I had assumed it would've been addressed in a software release by now. However, It is still occurring, many releases later.

I have heard from others who have noticed this problem, although maybe not to the extent I have picked up on it. Since I have the proper metering in line at all times, it is quite evident.

This still needs to be addressed. Prior to switching back to the Flex-6500, I have been using my ANAN-100D for the past few months. It also is set up to use CESSB compression, and I have had no issue with power spikes whatsoever. None at all. Same audio chain, same power supply, same linear amplifier, same meters, same antenna, same everything. The only difference is the exciter.

Using the Flex without CESSB compression is almost unacceptable at this point. The average talk power is quite anemic without it.

Eric
K2CB
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Jim K4JAF

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I am driving an Acom 2000a with about 45 watts here with the 6500 using either the DX or DX+ compression and don't see any over drive at all.  Perhaps there is a problem in the ALC of your Flex.  73s Jim K4JAF
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K2CB Eric Dobrowansky

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For what it is worth - I am running the TX bandwidth at 0-4000Hz.  Using the built in EQ, as well as outboard audio gear. And high average talk power due to external processing. So maybe that is why some see it and others do not.

I also own an Acom 2000A, and the spikes obviously occur with that amp as well, so the amp is not the issue. 

(Edited)
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Ken - NM9P, Elmer

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Try again with low end cut off at 50 instead of 0. You might be getting some strange rumbling crud in the extreme low frequencies?
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K2CB Eric Dobrowansky

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I was thinking along the same lines.  No time for radio this evening. I will try to experiment with the bandwidth settings tomorrow.


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Sergey, R5AU

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Eric, have you ALC connected ?
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K2CB Eric Dobrowansky

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Hi Sergey,

No ALC connected.

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Sergey, R5AU

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Behavior is not good, I am driving my 2k-FA with ~35watts where no spikes was registered, otherwise this amp has high sensitive overload protection circuit, I think in case no good results with EQ , to submit ticket suggested.
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Jim K4JAF

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What happens if you bypass the external audio gear and just use the 6500 with its EQ?

Sounds like your overdriving the input audio circuits of the 6500.  I hear so many of the ESSB guys on 20 who are way very wide..  Perhaps AM would be the solution to wide, HiFI type audio...



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K2CB Eric Dobrowansky

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It still does it when a microphone is plugged directly into the radio.

I keep my voice peaks between -10 and 0dbm, so I don't think it is over driven.

(Edited)
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Dudley - WA5QPZ

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Do you have a noisy environment or feeding some additional audio in ?    If you use the DEXP,  does the issue go away?   
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Sergey, R5AU

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Dudley, i guess DEXP expand dynamic range  down, but Eric have a problem with peaks over limited (with slider) output power.
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K2CB Eric Dobrowansky

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I tried it with and without the downward expander, with the same results. I am even using an external noise gate.
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Bill -VA3WTB

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You should put in a help ticket, over shoot is not common in the Flex radio.
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K2CB Eric Dobrowansky

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As soon as I get some more time to get back into the radio room, I plan to do some additional testing with filter bandwith settings, etc. Once I know the results, I will then post more detail, and/or submit a ticket.
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Tim - W4TME, Customer Experience Manager

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Do you have a scope trace of the overshoot?  It would be interesting to see the waveform and how long this transient is lasting.  This type of behavior reported very infrequently.
(Edited)
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David Decoons wo2x, Elmer

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Eric, I drive my Acom 2000 with drive level set to 45 which usually yields peaks between 1350 ~ 1450 watts out, depending on the band. This is measured into the Array Solutions Power Master II meter with SWR below 1.2:1.

I did have a big issue not long ago with my Astron SS-30 power supply where RF was getting back into the supply causing voltage instability. I took the power supply apart and disconnected the AC ground from the chassis and scraped the paint off with a Dremel. I then did the same for the circuit board to chassis connections. I installed four 10 nF silver mica caps in the following places: AC neutral to chassis ground, AC hot to chassis ground, DC + out to chassis ground, and DC - out to chassis ground. Now voltage regulation is measured at about 50 mV variation from receive to transmit at 100 watts carrier.

Since you are not that far, I can bring over my Flex and power supply next time I head down to visit my Mom in Manchester to test at your location. Give me a phone call if you would like to try that out.

73

Dave wo2x

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David Decoons wo2x, Elmer

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P.S. - I can bring some of the caps with me too :-)


I run 50 - 3500 with the W2IHY EQ and EQ Plus

(Edited)
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Paul, KB3ML

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This may dispel any concerns about Overshoot. 

Taken with my 6300 on 7.0250 @ 70 Watts. Sampled at -50dbm.    

The letter  F sent at 31WPM,

I tried many other power levels and bands but all proved to be identical.

Great job Flex  !

73. Paul


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Mike - N8MSA

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I monitor all transmissions with a scope, and I have seen zero overshoots from either of my 6700s. What I have seen is unexpected behavior, including shutdowns and transmission interruptions, in the presence of extreme RF fields: portable operation, with TX amplification, close to the antenna(s) and without feedline chokes. I haven't actually measured chassis and cable RF intrusion; I find it to be higher than previous Flex products but still isn't impervious to excessive RF "in the shack".

73,

Mike - N8MSA
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Paul Christensen, W9AC, Elmer

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Eric, do you see power spikes only in SSB mode?   Please try CW and report back to us.

Paul, W9AC
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K2CB Eric Dobrowansky

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Sorry for the delay in responding. Typical summertime activities have precluded time in the shack to play radio the past few weeks.  Anyway,  I made a few tests.....

The transmit bandwidth does not seem to make any difference.  Same with the EQ.  

When the processor is on, it is occurs frequently. However, it appears as if it does not occur with the processor OFF.  It is also more pronounced as the drive power is increased. At 20w, it is very little.  However, at 50w drive, the spikes are upwards of 70w.

As per W9AC's question, I tried CW, and there are NO overshoot issues whatsoever when sending CW.  I tried speeds from 5wpm up to 40wpm, and no overshoot was detected at any time.  

It appears to be SSB related only.

I only had limited time over the weekend, but I hope to experiment some more later this week.

Eric

K2CB


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Tim - W4TME, Customer Experience Manager

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Still need a scope trace if you have it on SSB.