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eHam Forums => Amplifiers => Topic started by: KD0ZGW on June 16, 2015, 12:38:30 PM



Title: Why are there recommendations both for/against use of ALC with amps?
Post by: KD0ZGW on June 16, 2015, 12:38:30 PM
Slightly confused rookie here.  Have done a lot of reading and seen advice several times that ALC is not needed and can cause problems.

If I understand it's function properly ALC provides a feedback signal from the amplifier is used to automatically limit the exciter output when the amplifier is at it's maximum output.  Seems like a good idea but there are an awful lot of amps and exciters out there and I assume they can't all be readily interfaced.

What am I missing?

Thx in advance for advice

'KD0ZGW


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 16, 2015, 01:14:08 PM
http://www.w8ji.com/alc_exciter_power_overshoot.htm


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: WA7PRC on June 16, 2015, 01:25:20 PM
http://www.w8ji.com/alc_exciter_power_overshoot.htm
W8JI explains it well:
Quote
ALC overshoot, or power overshoot, is caused by the basic flawed design of ALC circuits and RF power control systems. Normal ALC is like closing the barn door after the horse has escaped.

The problem is rooted in group delay times as the signal makes its way through the radio to the output port.
IMO, the best way to prevent overdriving an amplifier and without using ALC is to do the limiting AHEAD of the rig's microphone input. I use a Symetrix 528E 'Voice Processor' that has a compressor/limiter. After the amplifier is adjusted for best power AND linearity, I set the output level of the 528E to the point just below where the amplifier produces flat topping.

vy 73 es gl,
Bryan WA7PRC


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: WB2WIK on June 16, 2015, 01:47:32 PM
The power overshoot article is interesting but doesn't really answer the question.

This discourse addresses the actual question a bit better, I think; it's a discussion of one specific product that has an ALC subsystem that actually works well (I have one, and do use it all the time -- ALC is always connected).
Quote
I read on the Ameritrons' AL80B technical info that on this Amp is
> installed a "electronic bias" that is a known circuit and a " Dynamic ALC"
> that allows "high level, low distortion RF processing", doubling the
> average SSB power.
Hi Vince,

That's advertising fluff. Because the ARRL Handbook says
RF compression causes up to 3 dB improvement in "talk power", that
got put in the ad.

How much improvement it really makes depends on the ALC response time
of your rig, and how you run the rig.

Here is what the circuit does. Instead of sampling RF voltage at the
tube cathode, it samples grid current. Grid current is referenced
against an unregulated sample of rectified and filtered power
transformer secondary voltage.

One advantage of this system is if the transformer or power line
sags, the peak grid current is reduced.

The other advantage is if you set the ALC control to allow (for
example) 150 mA of grid current, you can never exceed 150 mA of grid
current under any tuning condition. That reduces your worry or
concern about arcing the tank circuit, overdissipating the grid, or
overdriving the PA from nearly any cause.

Any time the grid current starts to approach 150 mA (the circuit has
built-in hysteresis), negative ALC voltage appears.
Quote
> I believe that could be some sort of amplified grid current feedback to
> transceiver, instead of the standard capacitor partition of input signal.
That is correct.

That was written by W8JI several years ago.

Not all transceivers even have an external ALC input, and not all amplifiers have an ALC output; some work quite well, some don't.

The AL-80B's circuit seems to work well with anything I've ever connected to it.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM1H on June 16, 2015, 01:50:30 PM
Quote
W8JI explains it well:

But Ameritron still pushes it; sounds like double talking to me.

ALC was fine for vacuum tube rigs where only the final amp was controlled with a negative going voltage into the tubes bias circuit. Simple and usually effective. Its either the Chinese or Europeans who woke up and dropped it in some products.

I have a Daiwa processor now that does well and way back I had a modified Comdel into the CE-100V (A pair of very low distortion USA TungSol 6550's) and NCL-2000 that kept the 8122's under control. The built in scope on the 100V and a CE MM-2 after the amp helped; I still use all but the Comdel.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W8JX on June 16, 2015, 03:10:13 PM

IMO, the best way to prevent overdriving an amplifier and without using ALC is to do the limiting AHEAD of the rig's microphone input.


Not a good way at all and not sure why some think it is. When you suppress audio you also reduce peak to zero signal ratio. SSB output is usually rated that carrier is suppressed "x" amount of db below peak output at max output. As you reduce audio drive you reduce peak audio but carrier floor is same so you reduce effective talk power and compression. Best way is to NOT mess with audio and limit RF output power. It is not hard to do on a modern rig.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: WA7PRC on June 18, 2015, 12:11:44 PM

IMO, the best way to prevent overdriving an amplifier and without using ALC is to do the limiting AHEAD of the rig's microphone input.


Not a good way at all and not sure why some think it is. When you suppress audio you also reduce peak to zero signal ratio. SSB output is usually rated that carrier is suppressed "x" amount of db below peak output at max output. As you reduce audio drive you reduce peak audio but carrier floor is same so you reduce effective talk power and compression. Best way is to NOT mess with audio and limit RF output power. It is not hard to do on a modern rig.
We used limiters in broadcast engineering. There was no feedback from the PA to utilize. I presume that's still the case.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 18, 2015, 12:28:20 PM
You shouldn't use the mic gain to reduce power, but to limit peak power it is probably effective.  True, if one tries to reduce his rig from 100 watts to 10 watts using the mic gain, the carrier level to PEP output ratio is reduced, as well as spurious products from the mixing chain, etc.  But, using a limiter is a different animal.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KD0PO on June 18, 2015, 12:29:10 PM
FWIW alpha doesn't put an ALC jack on the 9500...


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM3F on June 18, 2015, 12:58:57 PM
There is a lot if dynamics to all this.
You cannot mix up audio peak limiting with Auto Limit Control even though they work together but in a separate ways and different in timing of the events.
I tune for max power PEP from the amplifier, then over Load for a small drop in power, then introduce ALC to see drops when peaks are reached.
This is seen when then ALC meter function rises off zero just a small amount on peaks.
You cannot possibly overdrive with this setup.
I uses an 8 band in the audio chain to boot and works very well.
No one has ever saw artifacts from my signal at 800 watts using an AL80B and Kenwood TS2000 that would even approach splatter or QRM off frequency..


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KD0REQ on June 18, 2015, 02:57:12 PM
~PRC in broadcast had a fixed system.  the feed to the class-A line or the digital stream from the studio goes into a speech amp at the transmitter with fixed, carefully adjusted gain into the modulator, carefully adjusted to tickle the RF chain just so, which is held very closely on the same frequency into the same rugged antenna field.  broadcasters are commercially monitored (at least in my day) on an average monthly for frequency, modulation, quality of signal, and regularly for coverage.

the only thing that's a wild card is the programming leaving the studio.  Joe Fogey's Sinatra Hour is going to be barely tickling 0 dB.  Wild Harry's Rockin' Saturday, the VU meter is going to be bouncing off the peg because it sounds best on the studio speakers, and it makes the bass bodacious on every thump.  for that boy, you really need audio shaping and a good limiter.  stations make their sound by choice of mike and adjustment of the Orban.  I remember the kid's AM station when I was in college would splat out multiple times whenever they played "How Can I Mend A Broken Heart."  confirmed a semester later when one of their jocks was in my classes they had a bad power supply, and it took a while to locate parts.  they could have dialled down the processing, but no... they had That Sound to preserve.

hamming, nothing is stable.  antennas fluctuate, spinning up and down the dial, no visual signal big as life to indicate how you're modulating, working the mike all over.  you need oopsie control on the power and shaping control on the mic amp.  the first is ALC and the second is your compression.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KK5DR on June 18, 2015, 05:01:26 PM
I've been saying it for decades now, that not using ALC is a receipt for damage to your gear.
In today's fully solid state amateur stations that run up to 1kw, not using ALC is going to come back to bit you some day. ALC in this type of station does a number of function besides power limiting. It is tied to SWR, excess device collector/drain current, combiner/divide imbalance, imbalance device pair current, device gain imbalance, incorrect band selection, etc. any one of these parameters has the potential to fail, or be tripped. ALC is used to "throttle back" the exciter output to a safe level that can save the amp from further damage or misoperation.
In regards to a solid state exciter driving a tube type amp, I say use ALC here as well. The only exception being an amp that can handle the full instantaneous RF power output of the exciter. If you use an amp that has very high gain tube(s) in it, those tubes can and will be damage over the long term by excessive drive. In a conversation I had with Reid Brandon (Chief engineer with CPI/EIMAC), he told me that 90% of all tubes that fail in amateur service, do so because of chronic overdrive. He said they aren't complaining at EIMAC, it's more business for them.
The simple use of a properly adjusted ALC system would have saved at least 75% of that 90%.
A properly adjusted ALC feedback system will not cause and harm of any kind to the transmitted signal.
You ask, "How is ALC adjusted properly"?
You simply tune your amp as normal, to the desired full output. Leave the exciter drive level set to the point where that output was tuned to.
Raise the ALC adjustment by turning the screw on the back of your amp(front on some), turn it till you see the full power output of the amp just begins to drop by a few watts.
That's it, your done, the threshold is set.
Mind you, the exciter drive level most be left in that same spot at all times. It's only at this tune point that the system is calibrated. Change the exciter output above that tune point, the system goes into ALC loop instability which causes RF compression, and this isn't the linear RF compression used in early stages of the exciter PA. No, this kind of compression is very nonlinear, and distorted.
Keep the exciter drive in the calibrated state, and the transmitter is as clean as the exciter/PA were designed to make it. There will be no detectable artifacts on the stations transmitted signal if the system is well calibrated.
This does not apply to mic gains set too high, heavy audio compression, etc. we are discussing only the RF power output of the amp.
I personally never operate any of my Amps without a properly calibrated ALC system in operation. I've never had any problems with distorted RF power out, when my station is operating normally. I'm usually QRO when on phone.
Here is a fact many hams may not know: All commercial and military high power HF comm systems use ALC. it's design in such a way that should there not be a detectable ALC loop current, the HPA is disabled and an alarm is indicated on the exciter display. These systems are fully automated and preset in ROM in the exciter. When the HPA is connected by the proper cable connection, the system "hand shakes" with the processor in the HPA and the system is set. No operator need interfere with it.
Commercial and military gear are designed and built to far higher standards than any ham gear could ever be made. Firms like; R&S, RFHarris, Rockwell/Collins, Thales, Marconi, Racal, etc, all have this type of ALC system for their HF comm systems.
If you decide to not use it after reading all that I have said here, then you get whatever comes with that decision.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W8JX on June 18, 2015, 05:43:27 PM
Sorry but pretty much be. ALC is not needed if you know how to properly use your equipment. I have never used it and never will. It is a throw back from tube radio days when there no easy way to limit drive.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM4AH on June 18, 2015, 07:25:30 PM
Depends on the tube or tubes and depends on the rig. If you are driving a single 8877 tuned for 50 watts PEP and the rig is hitting 150 watt spikes or more at the beginning of a syllable you may not like it much long term. Processing is fine as long as you are not the one listening to it.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W8JX on June 18, 2015, 07:35:15 PM
Depends on the tube or tubes and depends on the rig. If you are driving a single 8877 tuned for 50 watts PEP and the rig is hitting 150 watt spikes or more at the beginning of a syllable you may not like it much long term. Processing is fine as long as you are not the one listening to it.

I really like this 150 watt spike bs.  Next it will be 200. If this was remotely true there would be a lot of blown 8877's. I think some kinda make it up as you go to justify need for ALC and besides the ALC voltage developed is AFTER any spike dah...


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM4AH on June 18, 2015, 09:20:41 PM
Depends on the tube or tubes and depends on the rig. If you are driving a single 8877 tuned for 50 watts PEP and the rig is hitting 150 watt spikes or more at the beginning of a syllable you may not like it much long term. Processing is fine as long as you are not the one listening to it.

I really like this 150 watt spike bs.  Next it will be 200. If this was remotely true there would be a lot of blown 8877's. I think some kinda make it up as you go to justify need for ALC and besides the ALC voltage developed is AFTER any spike dah...

Maybe you did just fall off a turnip truck last night. This is a well known problem with several rigs along with mods to try and correct it. And yes, there are a lot of blown 8877's because of it.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: G3RZP on June 19, 2015, 04:26:43 AM
ALC spikes are a fact of life. The gain of the RF chain isn't wound back until the output (or whatever the threshold is) is reached. So it is shutting the stable door after the horse has bolted. How far the horse has gone is dependent on the design - if the gain control stage is between balanced modulator and filter in a 'classic' rig, there's the group delay of the filter in the mix, and if it's multiple conversion with several filters, the group delays add up and the spike can have appreciable width just because of the delay in the signal getting from the controlled stage to ALC detection. It can often be seen on the first dot of a CW transmission.

When I got my ACOM 1500 amplifier, it was very noticeable that even at 400 or so watts output, (about 15 or 20 watts from the transceiver) the power spike was enough to frequently trip the amplifier protection circuitry. So I've removed the ALC......Even 30 years ago, Yaesu were relying on ALC to set the tx gain, and so the spikes were there. With tube amplifiers such as the FL2100 , it wasn't so much of a worry, but SS amps can die that much faster when overdriven.

When using AM or partially suppressed carrier, ALC is a no-no, because of carrier 'pumping' during pauses in modulation. The old Marconi automatic tuning transmitters had a motor driven variable attenuator in the drive line, and during the tune up phase of the automatic tuning cycle, it would adjust for the correct output level and then sit there until the next tune up sequence. It would be easy to do that with a digital switched attenuator now, of course, although that wasn't really an option in the late 1950's.

ALC was originally used to help prevent overdrive on speech, and would detect the onset of grid current in the PA. A dual time constant was sometimes used as well, but as soon as compatible AM or CW was required, the complexities of power spikes and pumping came in. When ALC is used as the sole gain control, problems are to be expected.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W8JX on June 19, 2015, 05:17:42 AM
Maybe you did just fall off a turnip truck last night. This is a well known problem with several rigs along with mods to try and correct it. And yes, there are a lot of blown 8877's because of it.

The blown 8877's are not from spikes but rather operator error as it is easy to damage control grid if not tuned properly. Nobody ever talked about ALC overshoot until 590 had a issue that has long been fixed and now all some talk about is ALC overshoot until some new problem takes center stage. There seems to be a new breed of hams that do not know how to properly use equipment and they depend on it being plug and play and bitch when it is not.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 19, 2015, 10:40:27 AM
I'm not sure about momentary transient current spikes on a 8877 grid, but I would be very leery of any overdrive on a 3CX800 tube.  the effects of overdrive, even momentary, would appear to be cumulative. That's one reason I like glass power triodes/tetrodes, like 4-400, 3-500, etc. They are much more forgiving... and tubes like 4-400 are still available and cheap.

Pete


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: G3RZP on June 19, 2015, 01:36:03 PM
For a home brew HF amp in the US, from a viewpoint of robustness and cheapness, an amp with three 4-400s in GG with about 3500 to 4000 on the plates is very attractive. The difficult part is  about 44 amps at 5.0 volts after the filament choke......Use 4, and series the filaments to need  28 amps at 10 volts, with some unbalance current in the neutral lead of the 5 - 0 - 5 volt filament transformer. If push comes to shove, you can use 4-250s and on SSB, you can over run them.

But it isn't going to end up small!

OK, I'm agreeing with Pete, K1ZJH.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W8JX on June 19, 2015, 02:35:22 PM
Use 4, and series the filaments to need  28 amps at 10 volts,

Or simply use 2 for 14 amps at 10 volts and give up only a few db.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: G3RZP on June 20, 2015, 01:36:05 AM
Quote
Or simply use 2 for 14 amps at 10 volts and give up only a few db.

Yes, you would give up less than 3dB and you can push a pair of 4-400 in AB2 grounded cathode to over 1500 watts at audio, so allowing for tank circuit losses, it should be possible to get 1500 watts at RF. Even in GG, you will get around a kW out of a pair with 4kV on the plates.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: N6PJB on June 20, 2015, 11:53:02 AM
Sorry but pretty much be. ALC is not needed if you know how to properly use your equipment. I have never used it and never will. It is a throw back from tube radio days when there no easy way to limit drive.

I agree with this.  ;D


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W4KVW on June 20, 2015, 12:06:42 PM
I for one do use the ALC adjustment on my ICOM PW-1 amplifier.Without the ALC the amplifier comes close to legal limit output even at 35 watts of drive.It is a simple adjustment & without doing so with these amplifiers the life span is short from what I have read & heard from those who failed too do so because they thought they were smarter than the folks who designed & built the amplifier.The amp works as it should at full output on all bands from 160 meters thru 6 meters with just 35 watts of drive.It has done so with two different transceivers (ICOM 756 PRO II & ICOM 7600) so that is how I will continue running it here.Whatever makes you happy with your gear but I'm leaving mine as it is.  ;)   ;D   :)

Clayton
W4KVW


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 20, 2015, 01:37:09 PM
Yes,  that is where the problem comes in--when an exciter has considerably more output than is needed by the amplifier.

I don't run ALC on my SB-220, and according to my monitor scope my 100 watt exciters are not capable of driving in into compression.  That, with careful loading seems to keep things running smoothly.

Pete


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: G3RZP on June 20, 2015, 02:51:06 PM
I don't know about other rigs, but I do not like the Yaesu reliance on ALC.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: AD5X on June 20, 2015, 04:13:34 PM
I don't know about other rigs, but I do not like the Yaesu reliance on ALC.

My ICOM IC-706MKII put out a 140-watt 2-ms spike regardless of the transceiver's power setting.  I.e., even at the normal 100-watt power level, there would be the 140-watt spike.  And if I set the transceiver to minimum power (about 5-watts), there would still be a 140 watt spike.  After the spike, the transceiver's ALC would control the output to the power set-point during the transmission period.  Once you had about 5-seconds of transmission inactivity, you'd get another 140-watt spike.  My IC-706MKIIG was a little better.  It would spike to 110 watts regardless of the power setting.

All easy to see on a good peak-reading power meter (I have an Array Solutions Powermaster) and/or a good oscilloscope (like my Tektronix TDS-2022B).

Phil - AD5X


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM1H on June 21, 2015, 12:48:15 PM
Quote
I've been saying it for decades now, that not using ALC is a receipt for damage to your gear.

Nonsense, there is no such thing as a blanket statement here.

Quote
n regards to a solid state exciter driving a tube type amp, I say use ALC here as well. The only exception being an amp that can handle the full instantaneous RF power output of the exciter. If you use an amp that has very high gain tube(s) in it, those tubes can and will be damage over the long term by excessive drive. In a conversation I had with Reid Brandon (Chief engineer with CPI/EIMAC), he told me that 90% of all tubes that fail in amateur service, do so because of chronic overdrive. He said they aren't complaining at EIMAC, it's more business for them.
The simple use of a properly adjusted ALC system would have saved at least 75% of that 90%.
A properly adjusted ALC feedback system will not cause and harm of any kind to the transmitted signal.
You ask, "How is ALC adjusted properly"?
You simply tune your amp as normal, to the desired full output. Leave the exciter drive level set to the point where that output was tuned to.
Raise the ALC adjustment by turning the screw on the back of your amp(front on some), turn it till you see the full power output of the amp just begins to drop by a few watts.
That's it, your done, the threshold is set.

A lot more nonsense.
Most amps ALC are not compatible with SS and the rigs built in loops are self contained.

OTOH rig overshoot is a huge problem that is the real cause of tube failures and the only cure is to get a new rig that works properly. If Joe Sixpak is driving his 8877 with 150W and excessive grid current then the a'hole deserves to lose the tube. OTOH if he has it set at 50W and low Ig and his piss poor designed rig nails the amp at 200W then he should sue the ass off the rig manufacturer.

Quote
I personally never operate any of my Amps without a properly calibrated ALC system in operation. I've never had any problems with distorted RF power out, when my station is operating normally. I'm usually QRO when on phone.

And I havent used ALC since I sold the Drake C Line around 83 for a TS-930. Monitors were made to allow users to set up their equipment. I started with an old O'scope for AM, graduated to a CE-100V with a built in monitor and a CE MM-2 on the output of the NCL-2000 in 1965; I still have and use them. A SM-220 came next and I still have it plus I moved the old HP 141T spectrum analyzer to the operating bench when I upgraded the main service bench.

Quote
Here is a fact many hams may not know: All commercial and military high power HF comm systems use ALC. it's design in such a way that should there not be a detectable ALC loop current, the HPA is disabled and an alarm is indicated on the exciter display. These systems are fully automated and preset in ROM in the exciter. When the HPA is connected by the proper cable connection, the system "hand shakes" with the processor in the HPA and the system is set. No operator need interfere with it.
Commercial and military gear are designed and built to far higher standards than any ham gear could ever be made. Firms like; R&S, RFHarris, Rockwell/Collins, Thales, Marconi, Racal, etc, all have this type of ALC system for their HF comm systems.

You forgot to mention that military and commercial gear has no mike gain or power controls and the gear has to be compatible with a wide range of voice levels of all 3 sexes. IOW your comment is totally incompatible with the subject under discussion.

Quote
If you decide to not use it after reading all that I have said here, then you get whatever comes with that decision.

Not using ALC will likely help more than the other way around and with monitoring being built into more gear the whole issue will go away soon.

Carl


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM4AH on June 21, 2015, 01:07:58 PM
Maybe you did just fall off a turnip truck last night. This is a well known problem with several rigs along with mods to try and correct it. And yes, there are a lot of blown 8877's because of it.

The blown 8877's are not from spikes but rather operator error as it is easy to damage control grid if not tuned properly. Nobody ever talked about ALC overshoot until 590 had a issue that has long been fixed and now all some talk about is ALC overshoot until some new problem takes center stage. There seems to be a new breed of hams that do not know how to properly use equipment and they depend on it being plug and play and bitch when it is not.


That is interesting since Collins had a service bulletin dealing with ALC overshoot dated 9-2-60 .  Many rigs have had spikes including the IC-781 which I think may predate the TS590 a couple of days. My TS-940S would hit a 150 watt peak occasionally with the power set at 100 watts that was at a long enough duration that you could see it on  a PEP wattmeter.

And no, I don't use ALC amp control and never have so I am not defending anything. I use amplifiers with tubes that are more immune.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM1H on June 21, 2015, 01:47:23 PM
ICRAP lead the industry in ALC overshoot going back to the early 80's and their first SS xcvr. I'll never own an ICRAP after evaluating many models for the YCCC back then.

Currently use a TS-940 with lots of mods and a stock TS-950SD. Havent burped an amp yet including those with very touchy tubes such as NCL-2000, Alpha 76PA, Dentron DTR-2000L, MLA-2500, which are in regular use plus a SB-230 for portable use with a little TS-130S. Im sort of a confirmed Kenwood guy but they havent built anything since that interests me. Owned a FT-1000D for awhile but kept the 940 since it was gone in 90 days. Also tried some high end Ten Tec trash back then.

Guess that is why I went from GM Buick/Caddy to Ford/Mercury and the latest is a 2015 Fusion Titainium model.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KB1GMX on June 21, 2015, 03:20:52 PM
On the Tempo-One at full drive it would overshoot and flat top. especially on
40M for some reason.  This is a glow in the dark radio with traditional ALC to
its finals.

The solution was grid and plate loading resistors to tame the gain so it was
not hitting the final so hard to start with.  Then the ALC was dial back so it
behaved smoother.  After that not an issue.

Most of the generation of solid state DC to daylight radios have far to much
RF gain in the transmitter lineup.  On a TS-440SAT also a alc spiker a
carefully placed 7db pad really calmed it down and with no other changes
got me better audio reports at full power.  Before it was mostly ok when run
reduced power.  Now its possible to flat top but only with excessive mic gain.
Likely that will save the finals as hammering them is not a good thing.

Far to many radio have power spikes most to their point of clipping but if you
winding back to 35 or 70W that's still a problem.   A far better way would
be a power attenuator to both cut the power while letting the radio run near
max and also assure it a excellent SWR into the amp.

I've done the above with many of my 100-300W Solidstate amps especially
the MOSFET amps as they do not tolerate excess power at all.  By excess
I mean a 350W amp that needs 8W for full power and 20W will fry the the
devices.  The goal being even if the radio spikes its not exceeding the
safe {no damage} input power.  Rolling the power back is both risky from
a possible spiking case but also operator error [oops forget!]/.

Allison

Allison


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM3F on June 21, 2015, 11:13:00 PM
The OP did not reference the equipment he uses.
Some radio models indeed spike, some a little some not at all.
I run both Kenwood TS2000 and 480 models with peak reading watt meters to observe and tune with and repeatedly have tested for spiking at full power and dialed back to 10 watts and rarely see a spike I would ever be concerned about.
I do not see it on the AL80B peak reading wattmeter either.
For some combinations of equipment  the spike could be a mike PTT key up response from the mike.
It could be a detection of audio from the radio speaker that may not cut off fast enough.
I use a home made PTT hand mouse to get away from some of these possibilities plus the delay time  selection in the menus.
I have driven 2m and 70 cm Transverters that only require less than a half watt and never lost them to spiking and drive into SS vhf amps.
Everyone is entitled to their opinion but not insist everyone else is wrong.
I think I have proven over time that ALC use, spiking in not an issue and other attributes work fine for me as I use them.
.
The use of audio limiters and compression in the audio  chain keeps the audio level under control.
Those who claim distortion results and those who miss use that function in total are misguided.
You hear it every time you turn on a commercial AM, FM or TV station and don't complain of distortion.
You do not use mike gain to control amplifier power as a normal way for transmitting.
If power level is decided on and the amplifier is able to do double that, then get a smaller amplifier and run it at is was designed for.
.
In the output chain, ALC can be used to attain max usable clean power with it's absolute limiting ability.
You have a spiking issue don't blame it on the ALC function.
Fix you spiking or get a different radio.
.
I run the AM mode as well and put up a signal comparable to the best out there  most of the time with the same equipment.
On AM mode I still use a little ALC but run the AM power full on and adjust amplifier drive and peak tune the amp with the carrier control at 400 watts.
The advantage is in a KW the audio  chain has it's own ALC  and will attack the modulation peaks if you don't take away that ability by using the carrier control as the rf drive control.
This is all verified by observing the AM peaks on a peak reading wattmeter.
If you don't do it this way, the voice peak pull the power back. Also seen on a watt meter in it's average reading function.
I set amplifier drive to a 100 watts carrier and see 100 x 4 = 400 x about 90& modulation or 360 watts AM peaks as I would expect to see..

Understand what you have and understand how to use it.
Good luck.

 


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 22, 2015, 07:46:55 AM
AM usually relies on peak limiters to avoid over modulation. ALC would seem to be a very poor choice for AM?  I also doubt that all peak detecting watt meters are the same in their ability to accurately measure power spikes with fast rise times of short duration. A scope is still the best method, for all modes.

Mike noise and other audio anomalies should be handled by a decent AGC system.  The is that the rigs with these problems will exhibit overshoot on CW as well as SSB.  I keep a monitor scope inline; and occasionally verify that nothing in my transmitter chain has changed for the worse.  Just my opinion.

regards

Pete


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: SA4MDN on June 22, 2015, 12:45:39 PM
well I disconnected my alc line a few months ago after reading negatives about using it, it is now connected again as in my haste to get a contact last night I forgot to turn the power down on the rig and pumped 200w into a 811h, got halfway through saying my call sign when I noticed the meters on the amp and the led bars on the ldg 1000 pro 2 tuner going nuts, lucky for me everything has survived my blunder, but for me that's a plus for using alc, makes me feel a little safer now from my own stupidity sometimes.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM3F on June 22, 2015, 03:10:18 PM
If it means anything the designer of the AL80B says a scope is not useful for reliably  seeing fast spikes and a good peak reading meter will show it as a stored spike for long enough to display it on the meter after it passes so you can tell at least there was one.
I find that to be true for the most part.
A very fast rise time on a Scope screen may not be seen due to brightness limitation on many scopes.
It's not that the Scope can't detect it it can't always display it on screen..
I have the AL80B peak meter in the amplifier, the ATR20 tuner  Peak reading meter that is the same circuit and an older WM-1 computing meter. They all see the same thing when it happens.
Good luck.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1QJ on June 22, 2015, 03:23:05 PM
an analog peak reading meter is useless.  A digital peak meter such as the LP-100a or the Powermaster holds the highest peak reading for a few seconds so you can digitally see a read out of the high spike power amplitude.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM1H on June 22, 2015, 06:08:19 PM
Quote
If it means anything the designer of the AL80B says a scope is not useful for reliably  seeing fast spikes and a good peak reading meter will show it as a stored spike for long enough to display it on the meter after it passes so you can tell at least there was one.
I find that to be true for the most part.

To be honest it doesnt mean much at all considering.... The reality is that the right scope or the right digital display is required to get meaningful results.

Carl


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KB1GMX on June 22, 2015, 07:16:14 PM
I've always used a scope, done right its the best way.  It can be done wrong.

The procedure I use is first set the radio up on a load, and a Bird, tune up and drive it
with a 1khz tone to max power (SSB) then drop it to the desired power less than full. 
Use your ALC or whatever drive control and then use a keyer or 555timer to send
dashes repeatedly and sync the scope to the keyer. If the radio has spikes they will
be there.  A good radio keys like a CW rig, with reasonable risetime (also fall time)
and no overshoot.  Unreasonable rigs will have blips at the leading edge.  Those blips
are overshoot or, as called here, excess power spikes.    Its the ALC responding
too slowly, excessively, and often the overshoot has undershoot afterwards as well.

NOTE if the scope has memory (old storage tube scope, or modern digital) its much
easier to do.  But a repeated pattern of keying the transmitter with enough gap its
easily viewed on any old scope.  I've found a keying rate of 2-5 a second is enough
with a on time of maybe 100 to 300ms. 


Allison



Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: AD5X on June 23, 2015, 05:13:35 AM
You need a 'scope that can catch and hold the leading edge of the first dit (or dah) of a transmission only.  The leading edge of that first dit is where you can see the overshoot.  A repetitive keying pattern won't show this, as the radio's ALC takes over within 1-2 ms and holds the power level properly for about 5-seconds.  So except for the leading edge of the very first dit, you won't see any overshoot with a repeating pattern.

You can use single-sweep and trigger on the RF signal.  Or trigger on the amp-key output of the radio and offset the trigger or display to properly view the leading edge of the first dit of the signal (the amp-key output usually occurs 5-10ms or so prior to the signal, and the overshoot is maybe only 1-2us in duration).

Phil - AD5X


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: ZENKI on June 23, 2015, 05:53:47 AM
Shortly you will able to buy an excellent monitor scope for monitoring over driving and capturing keying transient problems.

http://www.telepostinc.com/LP-500.html

The LP500 will be Ideal for monitoring these problems.

ALC overshoot on Tetrode and Solid state amps cause tremendous  amount of IMD and keyclicks.  This is especially so if the  amplifier is a low  drive amplifier.
The Latest Radcom has a review of the  SPE1.3KFA, besides having  terrible IMD performance the amp was very sensitive too ALC  and over drive problems which would be a
real disaster for the ham bands.

The other problem on  many amps is the horrible EBS designs that dont work well. They contribute more to causing splatter and keying transients than even ALC incompatibility.
EBS on any amplifier is best disabled just like ALC. You can always use an  SWR  or over power Alarm too protect your amp. The Array Solutions power master and MeterBuilder meters offer these features.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM1H on June 23, 2015, 05:46:35 PM
Quote
AM usually relies on peak limiters to avoid over modulation. ALC would seem to be a very poor choice for AM?  I also doubt that all peak detecting watt meters are the same in their ability to accurately measure power spikes with fast rise times of short duration. A scope is still the best method, for all modes.

You can see the results of an ALC dominated AM signal on any rig with a panadaptor/bandscope; it aint pretty and it sounds bad also.
Most amps require about 20W tops for a 350-400W carrier. Properly setup you can watch the upward PEP swing on the meter since it is 4X the carrier power.

SDR rigs such as the Flex 5000 sound absolutely great on AM and you can fully tailor the audio.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM3F on June 23, 2015, 08:08:09 PM
I feel that ALC does not do anything to create modulation flat topping as I perceive some here are thinking.
It does reduce transmitter driver power therefore amplifier output.
This is not flat topping or amplifier induced limiting because it all happen from the amplifier input stage not the output.
I set amplifier for 400 watts max power tuning for a more linear amplifier operation knowing my setup will not top about 360 watts PEP so should never reach ALC feed back levels and still stay within a more linear part of the amplifier operation.
Peak limiting back in the audio chain also helps with any tendency to overdrive any part of the chain plus it's other benefits.
It works for me without any obvious side effects.
Could it be better? sure but at what cost?
This is Ham radio not some commercial venture, so we use what we have.
You can peel  this onion as much as you like. Reality is we have what we have to work with.
100 different radios, 50 different amplifiers and endless combinations with different results.
 
Good luck.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: N3DT on June 24, 2015, 11:40:30 AM
I've got a TS2000 and AL80B with an LP100A wattmeter. I haven't looked at my signal on the scope yet (lazy) but I get lots of unsolicited compliments on my audio. I tune the AL80B to about 750-850W (depending on the band) on FM and drive it with about 70-75W from the TS2000. I do run up the mike compression a bit and I haven't tried playing with the ALC yet although it's hooked up but I've got the ALC set turned all the way to 10. I haven't seen any over shoot from the TS2000 even when running 10W into the LP100A. It seems to be a good combination, even with the HH mike. I can't complain and I only gave $900 for the AL80B.

I do notice the AL80B watt meter doesn't always agree with the LP100A but it's probably within 10-15%.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 24, 2015, 12:30:43 PM
Audio quality doesn't mean a thing. Nothing. You can be running the amp  into severe gain compression on peaks, and still have great audio reports, while you're buck shooting crap across most of the band. Lord forbid one uses ALC to ensure constant flat topping.  Instead of IMD bursts every few seconds on peaks, we are treated to a constant barrage of ALC induced products. ALC is not speech processing, nor an effective limiter.  It is designed to capture  random syllabic peaks.

Pete


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM4AH on June 24, 2015, 01:10:03 PM
Audio quality is subjective. I like somebody to sound as close as possible to the way they would in person, not the way they have God sounding in the Ten Commandments.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM3F on June 24, 2015, 06:28:33 PM
Some can manufacture various scenarios all day long to justify there positions.
If my equipment was shot gunning anyone, I would have been told about it looong ago.
I have heard others doing it but was no use to tell them with the attitudes they display.
Ever hear the response 'it must be your receiver' or get a new radio!
I say yep!    It's you trash my receiver is hearing.
Good luck.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 25, 2015, 09:26:27 AM
I haven't looked at my signal on the scope yet (lazy) but I get lots of unsolicited compliments on my audio.

That statement shows the problem with your position. You could be running near Class C, and still receive good audio reports. Truth is, unless you test and monitor, you will never know how garbage the other guy is hearing is actual IMD products from your transmitter, or RX overload on his end.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: AF6LJ on June 25, 2015, 10:40:02 AM
I don't know about other rigs, but I do not like the Yaesu reliance on ALC.

My ICOM IC-706MKII put out a 140-watt 2-ms spike regardless of the transceiver's power setting.  I.e., even at the normal 100-watt power level, there would be the 140-watt spike.  And if I set the transceiver to minimum power (about 5-watts), there would still be a 140 watt spike.  After the spike, the transceiver's ALC would control the output to the power set-point during the transmission period.  Once you had about 5-seconds of transmission inactivity, you'd get another 140-watt spike.  My IC-706MKIIG was a little better.  It would spike to 110 watts regardless of the power setting.

All easy to see on a good peak-reading power meter (I have an Array Solutions Powermaster) and/or a good oscilloscope (like my Tektronix TDS-2022B).

Phil - AD5X

I have two Icoms an IC-745 and an IC-756 The 745 doesn't generate the spikes it is a very well behaved radio. The IC-756 (non pro) generates 150W+ spikes and I wouldn't run it on a modern amplifier, not even on a bet. As for using the ALC connector on the back of my SB-220 I don't see any use for it here in this shack.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: WA7PRC on June 25, 2015, 10:45:05 AM
I haven't looked at my signal on the scope yet (lazy) but I get lots of unsolicited compliments on my audio.
Distortion has to be almost gawdawful before someone can tell by ear. However, it doesn't take much nonlinearity before your signal is as wide as the broad side of a barn. Odd-order distortion products are usually the most prevalent. Listening OFF FREQUENCY will give an idea of how bad a station is flat-topping.

A spectrum analyzer is the tool to use to get a definitive look at how wide a signal is. However, most SAs are not cheap and not the most convenient tool. The next-best is an oscilloscope. They're easy to use and can be inexpensive. I prefer a lab scope because they almost always have triggered sweep that blanks the display until a signal is present.

vy 73 es gl.
Bryan WA7PRC


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: N3DT on June 25, 2015, 10:54:41 AM
I have listened to my signal on another RX right here in the shack and it sounds fine, even tuning around. I'm certain I'd hear splatter with an S9+20 signal if it were there. I've also looked at my signal on my Moto spectrum analyzer and it looks fine thank you very much.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: W1BR on June 25, 2015, 05:35:51 PM
Transmitter IMD measurements require something a bit more substantial than the all-in-one two-way service boxes.


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: KM1H on June 25, 2015, 05:49:37 PM
Quote
Some can manufacture various scenarios all day long to justify there positions.

Yep and some do the ostrich thing and deny everything.

Quote
If my equipment was shot gunning anyone, I would have been told about it looong ago.
I have heard others doing it but was no use to tell them with the attitudes they display.
Ever hear the response 'it must be your receiver' or get a new radio!
I say yep!    It's you trash my receiver is hearing.
Good luck.

Do you have the equipment to evaluate your own signal?  If not you have no idea what is going out. Expecting someone to tell you on the air just doesnt happen these day of a PC world, same if you had BO....



Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: N0SP on June 25, 2015, 08:15:10 PM
    VERY few transceivers have fast enough ALC output to prevent overshoot and the resultant buckshot and dirty amplifier output.  The best and easiest method to absolutely limit the output of your exciter is to place an external negative voltage on the ALC terminal of your transceiver.  Use a 9v battery, wired through a 10 or 20-turn pot and place the adjustable -voltage on the ALC pin.  Key the transmitter in CW or TUNE position with the power control on the radio set to maximum, then adjust the pot until the power reduces to the level you want.  Then NO MATTER what you do with the audio or power control of your radio, it will never exceed the desired value.
    Another method used very successfully with many radios with RF processors (RF PROCESSORS only!, not "compressors") is to engage the RF processor and turn the processor level down to the desired output while whistling/yelling in to the mic.  I know this method works with many Yaesu radios. (generally not Kenwood, since they mostly use audio "compressors")  Hint: Turn down the processor's compression level (separate from the main front panel processor control) to a very low compression value to make it sound natural, not muddy/contestie.  This control is usually a seldom-used setting that is in the back of the radio or a more "hidden" menu. Set it to maybe 8 to 10db max.  The front panel processor control is the one you set while screaming at the mic.   This method works well with FT-102, 1000D, and later radios.  I have not tried it on others with RF processing.  These true RF processors pre-limit output without waiting for the radio's internal ALC to do the work.
   Others have suggested using audio limiting, but this is much trickier to do effectively unless you have some good equipment to monitor and carefully control the audio level in to the radio, many hams don't have the necessary tools to do this.
   All this being said, there are a few radios out there with a problem sending out a high power "spike" at key-up.  Make sure you don't have one of these radios, most that do have this issue have fixes for it available from creative users who have published them on the web. 
  I have never relied on ALC to tame an amplifier, but have heard hundreds of signals on the air with awful signals from people who do.  Meters will not tell you this problem is happening, only a properly connected scope with someone observing who is capable of interpreting the readings.
73,
Dennis
N0SP


Title: RE: Why are there recommendations both for/against use of ALC with amps?
Post by: G3RZP on June 26, 2015, 12:52:12 AM
 
Quote
The best and easiest method to absolutely limit the output of your exciter is to place an external negative voltage on the ALC terminal of your transceiver.  Use a 9v battery, wired through a 10 or 20-turn pot and place the adjustable -voltage on the ALC pin.  Key the transmitter in CW or TUNE position with the power control on the radio set to maximum, then adjust the pot until the power reduces to the level you want.

Sadly, even that isn't foolproof. I found this with the FT102: the stage to which ALC is connected is also a receiver IF stage, and so has AGC. This means time constants are such that the externally applied voltage isn't there all the time in receive and the transition time is slow because of multiple time constants, allowing a power spike. The Yaesu method for not using the processor is to always drive to full power and have ALC control things - so some bright sparks wishing to reduce output power recommend reducing the loading, which of course, means splatter. Using the FT102 without the processor is a somewhat disastrous process as a result.

Quote
Another method used very successfully with many radios with RF processors (RF PROCESSORS only!, not "compressors") is to engage the RF processor and turn the processor level down to the desired output while whistling/yelling in to the mic.  I know this method works with many Yaesu radios.


It's an improvement, certainly, but doesn't always help on CW, where the drive control is sometimes implemented in a similar system to using the external ALC and it still spikes.

For CW testing, I use my pulse generator and relay switch on the key line and use the VOX with minimum delay: the oscilloscope then really shows the power spike on the first dit, especially if one triggers the scope from the pulse generator.

Quote
Others have suggested using audio limiting, but this is much trickier to do effectively unless you have some good equipment to monitor and carefully control the audio level in to the radio, many hams don't have the necessary tools to do this.

Very true.
Quote
I have never relied on ALC to tame an amplifier, but have heard hundreds of signals on the air with awful signals from people who do.  Meters will not tell you this problem is happening, only a properly connected scope with someone observing who is capable of interpreting the readings.

Also very true!