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Author Topic: Radio Spikes, Amps, ARB-704 Question  (Read 3237 times)
KF6OCI
Member

Posts: 104




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« on: July 29, 2011, 05:07:14 PM »

I keep hearing about transmitter spikes(TS-590, IC-7410,etc.) and the
danger to an amp, if you use one.

The Amplifer-to-Transceiver Interface  ARB-704 is for spikes from
the amp to the radio.

QUESTION: Will it also buffer, prevent, spikes from the radio to the amp???

   Thanks,

      Dan
« Last Edit: July 29, 2011, 05:15:39 PM by KF6OCI » Logged
N3JBH
Member

Posts: 2358




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« Reply #1 on: July 29, 2011, 05:40:04 PM »

I think the question you are asking is if the radio for example is set up to say transmit 50 watt's and when you key the radio it puts out a brief 100 watt signal (ALC overshoot???) Will the ARB cure this? I can not see how it could that problem is a condition in the radio. If you asking if the radio would send a voltage spike to the amp's key line? I doubt that be a huge concern either. Where the ARB is nice is where you have a havea high voltage keyed amp with  modern radio that is low voltage and current keying. say a new rig keying a heathkit SB-220 that has never had the keying modification performed. I have heard of guy's making a stand alone voltage device to add to there radios ALC line in a attempt to avoid the over shoot problem but i never really heard of one that worked as again i THINK the problem lie's deeper in the radios circuitry. Hopefully W8JI will come in and give his input on this as i know he is very knowledgeable about the whole topic.  
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AD5X
Member

Posts: 1428




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« Reply #2 on: July 29, 2011, 06:03:29 PM »

The ARB-704 only buffers the transceiver-to-amp keying interface.  Most current transceivers can handle an amp keying interface of maybe 16VDC open circuit, and a few hundred ma when keying the amplifier.  And most modern amplifiers have an amp key input that is compatible with this.  Older amplifiers had a much higher positive or negative open circuit keying voltage, or even an open circuit AC keying voltage.  The ARB-704 simply interfaces the low voltage/low current amp keying output of modern transceivers with higher DC or AC voltage amp-key inputs of older amplifiers.

The spiking problem is RF overshoot that exceeds the set-point of your transceiver for a few milliseconds while the transceiver's ALC circuit decides where it needs to be.  I.e., while you may have set your transceiver drive level at the recommended lower level to drive an amplifier, some transceivers over-shoot this level to full power or even higher.  As an example, my IC-706MKII overshoots to 140 watts for about 2ms regardless of where the radio output is set.  I.e., even if I set the output to 5-watts, that radio will output 140 watts for 2ms and then it will throttle back to the set level.  This can be pretty hard on some amplifiers.  Other radios are much better.  My IC-706MKIIG overshoots 7-10 watts over the set point regardless of power setting - but that's a lot better than going to 140 watts.  I currently also have an Elecraft K3 which has no overshoot.  I really don't know about other transceivers as I've only measured mine.  You can measure the overshoot of your radio if you have a good true peak-reading watt meter, or an oscilloscope that will let you capture the overshoot. 

Phil - AD5X
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KF6OCI
Member

Posts: 104




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« Reply #3 on: July 29, 2011, 06:14:09 PM »

Thanks.
 
There are several people no longer using the TS-590, such as some
on the Yahoo TS-590 Group, because of concerns for their amps.
Some have stories to tell about the danger.

I was about to get  a TS-590, started looking at the IC-7410, joined
their Group, and they just discovered the IC-7410 is spiking more
than the TS-590 on SSB, they have contacted Icom.

I was wondering if the ARB-704 would buffer it, guess not, oh well.

"Hopefully W8JI will come in and give his input ..."   I agree, I'd like to
know if it really is a danger to the amp.

    Thanks
      Dan
« Last Edit: July 29, 2011, 06:26:07 PM by KF6OCI » Logged
K4TLJ
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Posts: 91


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« Reply #4 on: July 30, 2011, 07:08:41 AM »

I built the two db attenuator described in a recent QST article for a friend (N4JA) that had the overshoot problem driving an AL82 and an automatic antenna tuner with a TS2000. The attenuator solved the problem completely. He just sets the radio for 100 watts and leaves it there. The attenuator has a DPDT relay keyed by the radio which bypasses the attenuator resistors on receive.
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KF6OCI
Member

Posts: 104




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« Reply #5 on: July 30, 2011, 08:38:37 AM »


OK, is the "two db attenuator" something you can buy ready made
somewhere?

Can you tell me what month of QST was the article in?

 Thank You,

      Dan
« Last Edit: July 30, 2011, 08:56:18 AM by KF6OCI » Logged
AD5X
Member

Posts: 1428




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« Reply #6 on: July 30, 2011, 09:06:16 AM »

The 2dB attenuator is in the "Articles" section of my website at www.ad5x.com.

Phil - AD5X
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KF6OCI
Member

Posts: 104




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« Reply #7 on: July 30, 2011, 09:13:38 AM »

I just left the ARRL site, you can't download it, saw it was
Phil Salas AD5X, it rang a bell.

 Thank you very much.

     Dan
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K0BG
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Posts: 9863


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« Reply #8 on: July 30, 2011, 10:41:44 AM »

Except for one or two, all solid state radios have a leading key down spike. Some of them, like the 706, is near 150 watts. There is a case to be made, where the spike might cause a problem with an amplifier. Phil's solution certainly eases the pain so to speak, but does nothing for the spike itself. 

I don't remember where it is, but Tom, W9JI, does have information about this subject on his web site.
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NO2A
Member

Posts: 783




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« Reply #9 on: July 30, 2011, 07:43:28 PM »

Someone on here had said there`s a software mod for the TS-590s to prevent these power spikes. Apparently on newer production runs. Maybe someone can comment on this.
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KF6OCI
Member

Posts: 104




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« Reply #10 on: July 31, 2011, 08:41:43 AM »

From what I can gather a software mod was done
by kenwood, but contrary to reports saying it corrected
the problem, knowledgeable people who say they have
tested it, say it just reduced it some, and it still is at
too high a level.

I don't know, would like to know if a high level really
is such a problem for an amp.

Seems like if this was such a problem amps would be going
out all over the place, doesn't seem so.

I'm interested in the effect on the new Elecraft solid state
amp, KPA500.

   Dan
« Last Edit: July 31, 2011, 08:44:43 AM by KF6OCI » Logged
W8JI
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Posts: 9296


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« Reply #11 on: July 31, 2011, 09:53:24 AM »

http://www.w8ji.com/alc_exciter_power_overshoot.htm

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KF6OCI
Member

Posts: 104




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« Reply #12 on: July 31, 2011, 12:13:44 PM »



   Very Good, Thank You.

      Dan
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AA4HA
Member

Posts: 1434




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« Reply #13 on: July 31, 2011, 01:27:09 PM »

If you were using something like an external PTT key line you could create a small digital circuit that would delay the PTT to the amplifier by 20-50 mSec. If the amplifier has a built-in PTT key you may be able to make a component value change (bigger capacitor value) in the transmitter sense circuitry to build that 20-50 mSec delay into the amplifier.

I can see where the "instantaneous on" behavior of a solid state amplifier could result in "instantaneous magic smoke release". A tube amp would be much more forgiving and probably has an inverse curve on the transmitter power level rise.

If you were to delay the PTT action the one area where it might affect performance would be in a digital mode where you would need to delay your RTS/CTS response (if using a EIA-232, full handshaking interface) so data is not being sent during the "quiet period" while the amp comes up to speed. Different sorts of tricks would be needed if you "key on data" without handshaking.

Tisha Hayes, AA4HA
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W8JI
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Posts: 9296


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« Reply #14 on: July 31, 2011, 01:49:05 PM »

If he delays keying the amp, it can cause multiple other problems. :-(

The amp always should be on and ready  before RF appears.
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