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A Peak Limiter for a Super Senior Transmitter




 
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July 16, 2018, 02:45:34 AM *
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Author Topic: A Peak Limiter for a Super Senior Transmitter  (Read 869 times)
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W6TOM
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« on: April 01, 2018, 05:54:27 PM »

  I have the 80/40 meter K7DYY Super Senior transmitter, I get occasional over modulation lock outs which are annoying. I'm using a D-104 with the K7DYY audio board.

  Any suggestions for a peak limiter that I might use that has a reasonable price?
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N1BCG
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« Reply #1 on: April 01, 2018, 06:24:17 PM »

Funny you should mention this. I’m faced with the same scenario for a 160/80 Super Senior. I like the b’cast processors the best. The Inovonics 222 comes to mind, although some consumer compressor/limiters have respectable peak limiting capabilities.

In that category, the DBX 166XL “Peak Stop” circuit works remarkably well although it would be wise to follow it with a LPF due to its hard clipping characteristics. The Symmetrix 565 has more of a limiter than clipper in its final stage, for example, and can drive a transmitter directly.

There are several newer models that are quite usable as well and you should only need 0dBm for 100% modulation despite the jack being called a ‘Mic Input’.

BTW, are you experiencing ‘power creep’? I’ve seen more than one case of these transmitters with outputs increasing above the set value and causing a shutdown. This defeats the effort to reduce power for less than perfect load matching.
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W6TOM
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« Reply #2 on: April 01, 2018, 07:00:17 PM »

 "Power Creep" is very noticeable, the shack is in my unheated garage that can range from the high 40's in Winter to 90 in the Summer. I have set carrier power to 250 watts but it drifts around with temperature and also the power level and over modulation lock outs appear to interact, making the lockout issue more likely at higher power levels.
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N1BCG
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« Reply #3 on: April 01, 2018, 07:22:23 PM »

I wish Bruce would add an APC circuit to actively control power and compensate for component heating. That, and an LED to indicate -100% modulation and/or a limiter.
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KD6VXI
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« Reply #4 on: April 02, 2018, 10:39:16 AM »

Is it a negative or positive peak condition that causes this?

If negative, the flex circuit Steve published with a negative peak limiter in it would suffice.  I've built a variation of it and used it for years with different xmitters.  It does perform best DC coupled to the modulator.

If positive, any broadcast peak limiter.

Almost everyone I've spoken to on a dyy love it, and they all drift in carrier power.

--Shane
KD6VXI
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Steve - K4HX
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« Reply #5 on: April 02, 2018, 09:17:49 PM »

Look for a CRL PMC 300. It's a split band peak limiter with switchable preemphasis. They can be found for $100 or less these days. I've been using one since the late 1990s.
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w1vtp
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« Reply #6 on: April 02, 2018, 11:10:34 PM »

If you cannot find Steve's recommendation yet another consideration is a Samson S-Com Plus (be sure to look for the "Plus").

The attack time is very fast on the compressor. I don't recall the limiter response time is but it's a pretty fast unit.

I don't own this transmitter but I think the two limiting factors are 1) A comparator that looks at the output voltage and trips on assumed 1500 watts across 50 ohms and 2) Looks for a certain return [return loss] and trips if it is too high. I don't know if it's sophisticated enough to look at the forward vs return and trips if the return is higher than is allowed or just looks for a returned power [E / R].  

Phase rotation is of paramount importance if one is to run this unit at maximum power.  The VSWR  must be controlled and the PEP watts must be monitored accurately if one is to achieve maximum results.  Otherwise, do what everyone else does with these units and run the power down somewhere around 200 watts carrier. Try to manage the VSWR

I don't believe hitting the negative peak affects any trip points.
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Steve - K4HX
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« Reply #7 on: April 03, 2018, 07:05:33 PM »

More on the PMC 300 at the thread below.

http://amfone.net/Amforum/index.php?topic=35973.0
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W6TOM
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« Reply #8 on: April 03, 2018, 08:37:57 PM »

  I appreciate the advise, my main issue is over modulation lock outs but every once in awhile like last night I will get a SWR lockout, why I do not know.

   My antenna is a 130 foot ladder line fed dipole antenna using a Palstar BT-1500A tuner, I always adjust for best match and can get an almost perfect match any place on the phone band. Rechecking after the SWR lockout last night showed the match was fine.
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Patrick J. / KD5OEI
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« Reply #9 on: April 03, 2018, 09:45:09 PM »

"Power Creep" is very noticeable, the shack is in my unheated garage that can range from the high 40's in Winter to 90 in the Summer. I have set carrier power to 250 watts but it drifts around with temperature and also the power level and over modulation lock outs appear to interact, making the lockout issue more likely at higher power levels.

I thought that unit was sophisticated enough not to be affected by the temp range you mention.
Maybe rather than APC, which seems after the fact, a thermal sensitivity compensation would be closer to the root cause?
And then APC if trimming is needed? Just a thought.
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« Reply #10 on: April 04, 2018, 12:04:42 PM »

I have been using a Behringer Eurocom SPL3220 split band unit for some time now and and it works very well. It has both compression and limiting.

As far as SWR, sweep your antenna system as you may have an asymmetrical sideband response.

I.e., you may have low SWR at the center frequency, but the SWR may rise on the frequencies + and - on each side of the carrier.   


Phil - AC0OB
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w1vtp
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« Reply #11 on: April 05, 2018, 12:24:38 PM »

  I appreciate the advise, my main issue is over modulation lock outs but every once in awhile like last night I will get a SWR lockout, why I do not know.

   My antenna is a 130 foot ladder line fed dipole antenna using a Palstar BT-1500A tuner, I always adjust for best match and can get an almost perfect match any place on the phone band. Rechecking after the SWR lockout last night showed the match was fine.

All this thread is fine but to your specific situation, have you called Bruce and shared your problem with him?  He is pretty good about customer support including sending back the unit and diagnostics and repair / component upgrade. I think you have arrived at this point accepting your data that you are satisfying the PEP power & VSWR requirements.

I recommend you call Bruce,  GL, Al
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