Sluggish ALC response

David H. W5CAH

Many disregard ALC. I got that. I consider it a safety measure in case I **** up, ok.

The 6500 does respond to the negative going ALC from my Icom PW1 amp.  The voltage parameters from the amp are within the published limits of the 6500.  The problem is the 6500's slow response to the negative going voltage from the PW1.

Dudley with the help desk told me it's possible that a lag inserted to protect some amplifiers may be too long.  It take about 2 seconds for the PW1 to come to full power (1KW).  I see the sluggishness with my scope on the ALC line and on the ALC bar graph on the 6500 client.  Response is very quick when the amp is connected to my 756 Pro.  The ALC voltage from the PW1 goes negative quickly (normally) when monitored but not connected to the 6500.

My choice is to leave the ALC on by default for protection and turn it off once I am comfortable with the status of the radio.

KY6LA_Howard

Welcome to why I use DDUTL I used to run a PW -1 ith my 6700. If found ALC to be a PIA as it was a potential source of problems. On The Other Hand. If u use DDUTIL, you can set auto drive to make sure that u always have the correct drive to the Amp. Basically u then get rid of ALC The PW-1 is a fine amp but I replaced it with an Expert 2K-FA...more power and Much easier to remote control. No ALC needed.

David H. W5CAH

Would gladly do without ALC but seem to be having issues with tune power being at 100 watts unexpectedly. It could be me.

Tim - W4TME

I have added this report as a defect in our bug tracker for further investigation

David H. W5CAH

I have received no feedback or regarding the ALC problems with my Flex 6500 and ICOM PW1 amplifier.  As reported 10 months ago, the Flex 6500 responds sluggishly and erratically to the negative going ALC voltage from the PW1.

With ALC enabled on the 6500 and tune power on the Flex manually increased slowly and smoothly, the 6500 bucks or pumps back against the PW1 ALC voltage resulting in erratic 6500 output and resulting erratic PW1 input and output.  I've observed this repeatedly with a scope while monitoring the ALC line. The result is a sluggish 1500 millisecond rise time for sufficient output from the 6500 to drive the PW1 to rated output.

When my 756 Pro is driving the amp there is no delay.  The ALC action is very consistent and smooth.

The PW1 is a great amp and I plan to keep it. One of the questions I asked when I bought 6500  was in regard to the ALC problems I had read about.  I was assured by Flex management that the ALC worked correctly.  I love my Flex radio but would sure like to see it play nice with my PW1.

David Higginbotham

W5CAH

KY6LA_Howard

Dave
As i said above I used to run a PW-1 with my 6700 and 5000 for years before I bought the SPE 2K-FA in 2014.

Never used ALC..

Rather I optimized the amp drive level for each band and used Autodrive in DDUTIL to control the Amp. 

I do not have the tune power issue you mention.

No problems whatsoever...

Tim - W4TME

Do you have scope traces that show this that you can share with our engineering team?

David H. W5CAH

Thanks for the reply Tim.  I can shoot some video of the scope, Flex & PW1 displays demonstrating the problem.  How is the best way to get the resulting files to you?

David H. W5CAH

Thanks for the comment Howard.  I want the ALC to be a safety net for my PW1. I know DDUTIL can set the drive per band but really don't want to complicate my setup with another service or program.  I'm striving to have the same ease of operation as when I am using my 756 Pro with the PW1.  Did you try to use ALC on your 6700 when you had your PW1?

Tim - W4TME

send it to my first name @ flexradio.com

Tim - W4TME

I had a thought.  What is the ALC voltage range for the PW1?  Is it 0 to -10 volts?  If so, this could be the issue as the FLEX-6000s only take a 0 to -4 volt range

KY6LA_Howard

If I can recall correctly ALC needed a voltage divider with the PW-1... It's been almost 2 years ago...
I also seem to recall that the ALC Circuit on the PW1 is not that great as even when i was using an ICOM radio it caused distortion products..

BUT DDUTIL works so well and is so SIMPLE to set up that I quickly abandoned ALC.

I might note that my Expert 2K-FA can also use ALC and has a much more sophisticated ALC circuit which is less prone to causing distortion... But I quickly dumped ALC on the 2K-FA and went back to using DDUTIL..  No distortion issues now...

David H. W5CAH

Tim,  the PW1 ALC output is a negative going  0 to -10 fully adjustable.  The ICOM setup guide states "The exciter’s ALC input must be compatible with the PW1’s ALC output (negative-going 0 -4V)" 

The specifications indicate the ALC is adjustable up to a max of -10 volts 10K ohm impedance.  Setup procedure is to set ALC adjustment on PW1 fully counter clockwise, set exciter power to 100 watts output, with amplifier keyed adjust ALC to center of ALC scale on PW1 & observe 1000 watts output on PW1.  After I make the adjustment the ALC voltage is -2.3 volts at 1KW.
  

David H. W5CAH

Thanks again Howard.

David Higginbotham W5CAH

Tim - W4TME

RRR.  Try turning off the PROC and testing it.  I am wondering if the CESSB is messing with the overload/drive protection in the PW1

KY6LA_Howard

-2.3V @1KW... very little headroom in the ALC circuit when you are driving it with 100W

I suspect that if you look at the output of the PW-1 on a scope you will see that your are generating distortion products... and like Tim said, if you use PROC then you may also be over driving it...

I might also note that the ALC levels are very band, mode and antenna specific so while -2.3 V is all it needs to clamp it @100W to 1KW on say 20M SSB... it likely might need say -3.5 V on 15M CW

That is why I ultimately ended up with the DDUTIL solution as I could set maximum drive levels per band and per MODE.. which gave me much better looking distortion products.

Paul Christensen, W9AC

And yet another reason to avoid ALC unless matched as a system (e.g., a Collins transceiver with a Collins amplifier).  When the ALC system is designed by one manufacturer, a "meet me" point is established with a known set of voltage and feedback dynamics. 

Long ago, a systems committee should have been assembled to establish a standardized ALC voltage and dynamics structure so that all combinations of rigs and amps play better together.  Without dynamic IMD measurements, we're fooling ourselves into a warm and fuzzy feeling that we're doing something good. 

Paul, W9AC

Sergey R5AU

Paul, i am completely agree with "When the ALC system is designed by one manufacturer, a "meet me" point is established with a known set of voltage and feedback dynamics. " otherwise "Sluggish ALC" is a normal let me to say reaction for 2 "foreign" units in the chain even Sluggish is much better then other reaction in counterpoise. May a good point in this case to stabilize feedback dynamics is to set some capacitors in the ALC voltage divider to set smooth ALC characteristics - but this is very personal things for RIG-AMP combinations

KY6LA_Howard

@Paul

I agree with you completely on this...

The PW-1 has a very Primitive ALC Circuit which is very prone to causing all sorts of IMD issues.. Yes it may protect the Amp somewhat but my IMD measurements were so much better when I did not use ALC but rather set maximum drive levels by band and mode in DDUTIL

By contrast, the Expert 2K-FA has a very sophisticated ALC circuit that is designed to adapt to the ALC Characteristics of multiple manufacturers so it goes a long way to improving IMD.

However I still get much better IMD Measurements by setting maximum drive levels by band and mode in DDUTIL.

FYI- Steve K5FR is working with the API for the 2K-FA to give us much more control of the Amp from DDUTIL

James Del Principe

I know this is an old thread but has anyone found a solution for this ALC issue? I had never used ALC with my other amps in the past but recently, I built a Mercury IIIs amplifier and it is very sensitive to overdriving. The manual and some users suggest to use ALC to keep from killing the LDMOS.

I connected the ALC cable and enabled HWALC in the Tx band settings in my Flex 6500 running release 3.3.32.8203. Next, I followed the manual from Mercury on the ALC adjustment without success. It seems to take forever to build up the level from the flex. With ALC enabled, there is really no output and the adjustment procedure cannot be followed as written.

In the meantime, I have created profiles with limited power out to ensure safe operation. If, however, one of the sliders is up, it could **** the LDMOS very quickly.

Has anyone been successful in getting the ALC to operate properly? Has anyone tried this with the Mercury amplifier? My Thanks and Best 73, Jim KD1I

David Decoons, wo2x

Using the TX Band table to set power is way to go. Do not trust any ALC to protect LDMOS devices. Also use the Max Power setting to limit overall maximum power output in case you move the power knob.

Using the Power Genius amp and I do not have issues with overdrive. Just set your power and save the TX profile.

Dave wo2x

James Del Principe

Thanks, Dave. Yes, I have created transmit profiles but wanted to be sure it could not overdrive. I think the Power Genius amp does not have this problem in the first place. It seems easy to damage this device as the gain is very high and there are warnings not to exceed a certain power level - in or out.

I will set the max power on the Flex as you suggest. It looks as though this issue has not been resolved with the Flex ALC. 73, Jim

David Decoons, wo2x

The Power Genius design has several things designed to help protect itself

• Very fast shutdown in case of error. The amp starts to shut down in about 25 uS.
• Input attenuator adjusted for around 40 to 50 watts drive. The EU SPE amps take only a handful of watts in for full power, making getting hit with high power much worse on the LDMOS devices. Everyone wants a “low drive” amp but wind up using it with a 100 watt radio. Why?
• Dual 1500 watt LDMOS devices. This yields more headroom in the amp. You are not pushing the RF device in a single LDMOS design to near its limit.

Find the band that requires the most drive power then in SmartSDR setup, set the maximum power to that level. That way no matter what band you will not exceed that power level.

73

Dave wo2x