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Author Topic: Inital Power Spike IC-7300  (Read 4692 times)
VR2AX
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Posts: 799




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« Reply #15 on: May 22, 2017, 03:58:58 AM »

I wonder how Icom achieve the 50 watt limit in your Japanese version. I'm no expert on power spikes but it looks like a design issue combined maybe a marginal choice of amp for your driver.

Why did the suggest a bigger power supply?
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AC2RY
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Posts: 203




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« Reply #16 on: May 22, 2017, 05:13:47 AM »

The RMA-305 will drive to full output with 10 watts input. What is your power output on the 7300 set at and limiting the maximum power to 10 watts is a bit harsh for the ALC on a 100 watt radio.

The radio is the 50W model. Depending on the band, I drive the amp with anything between 7% and 15%. Anything more than that will cause the amp to trigger the safe mode.

One suggestion I read in this thread, but have not tried yet, is to set some TX delay. I wonder if that may make some difference.

Luca

For SSB I suggest to play with mic gain and compression settings - reduce gain and increase compression. Microphone equalizer setting also may help - reduce bass down. Also you may think about placing microphone further away from the mouth. Generally you should barely see ALC indicator moving when you speaking, or not at all. Of cause your power supply should provide 20 amps without significant sag (below 0.5 volts).

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KI7DUX
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Posts: 28




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« Reply #17 on: May 22, 2017, 05:19:19 PM »

Why did the suggest a bigger power supply?

Your guess it as good as mine. But I think it is more related to not having a clue, not knowing how to fix the issue, but still not wanting to replace the radio. Or they are aware of the flow in the design, but rather than admit it they rather blame some other random part of the system.

The power supply is rated for 40 Ampere and it is dedicated just to the amp, the radio has its own. I really doubt that the power supply is really the issue.

Luca
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AC6CV
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Posts: 296




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« Reply #18 on: May 22, 2017, 07:10:48 PM »

I've used a 7300 with an Acom 1500 (since last Sept) through many contests, and haven't noticed any spikes that would affect the amp. I had two hot switch faults that I remedied by changing the TX Delay from 10 to 15ms. I drive the amp with 60-70% power from the 7300 (1,300W CW; 1,500W Peak SSB), and #2 compression on SSB...no problem. I also use two Heil dynamic mics, with audio gain control at 65-70%. If I use VOX, the VOX gain has to be around 90% for proper activation.

73, Bob K7JQ
I agree. Many amateurs are unaware of the delay or don't use it for what ever reason and have problems. Icom has an adjustable delay. Kenwood, if I recall, just has a 20ms on or off delay. I set my 7300 and 7600 delay at 20 ms and have never had any problems.
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WA1RNE
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Posts: 986




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« Reply #19 on: May 24, 2017, 09:21:18 AM »

Quote
have this problem too. On SSB, occasionally, my amp goes in fault mode on keying down the PTT.

I prepared a video to show the overshoot measured with an Ameritron AWM-30B, that is supposed to show peak readings. The overshoot was clearly visible.

 Have you monitored just the IC7300 driving a dummy load with the same wattmeter at 10 watts, 15 watts and 100 watts?


 Here's a couple of observations and suggestions:

 - the RM Italy manual states the amplifier requires 45 amperes maximum at 13 vdc as opposed to 40 amperes.

-  the schematic shows the amp uses a peak power detector at the input and is supposed to automatically insert an attenuator pad at the input if you exceed 10 watts. If you exceed 15 watts the amp goes into protection mode and shuts down. So not including tolerances, you have a 10-15 watt window to work within before the amp shuts down.

 If no output overshoot is noticed after running the above peak power tests on just the 7300, the wattmeter may not be fast enough to see it.  An 8-10 dB pad at the input of the amplifier might be what you need at that point.

  ...WA1RNE

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KI7DUX
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Posts: 28




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« Reply #20 on: May 24, 2017, 06:17:06 PM »

Have you monitored just the IC7300 driving a dummy load with the same wattmeter at 10 watts, 15 watts and 100 watts?

Yes that is more or less what I did, apart the fact that the radio is the 50W version.

Here is the video: https://youtu.be/tBtiEeWFuvU

One thing that I completely forgot is that in the video the overshooting only happens with compression engaged. Is this expected?

Luca

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WA1RNE
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Posts: 986




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« Reply #21 on: May 26, 2017, 07:20:25 AM »


 Sorry, I meant 50 watts not 100, forgot you have the Japanese version of the radio.


 There is really only one way to get to the bottom of this:  you need to monitor the transmitter output at the dummy load with a digital storage oscilloscope.

 This will allow you to positively confirm output overshoot and will also provide some verification of the wattmeter dynamics.

 ...WA1RNE
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W3RSW
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Posts: 527




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« Reply #22 on: May 26, 2017, 05:57:10 PM »

My LP1-100A seems to latch on the biggest pep spike or signal it sees and holds on to that until the transmission drops to zero and next signal starts.  Grin. I run into this action mostly on AM where there's a constant carrier with varying overriding sidebands yielding PEP.

As others have mentioned The scope's the ticket for the last word, even an old Navy OS8 with the signal tied directly to the CRT plates via well endowed rear panel connectors. Shows everything when the shack lights are dim for that old green trace.  Don't blink.  Grin
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Rick, W3RSW
VK3BL
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« Reply #23 on: June 03, 2017, 03:54:22 AM »

The IC-7300 does indeed have a power spike, although it is only minor in my experience.  Any amp suitable for use with 100 watts drive should be fine.

Worse case scenario, build a 50 Watt 3dB attenuator and run that in line with your amplifier.  Most SS radios produce their cleanest signals around the 70% drive mark anyway.
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J.D. Mitchell - VK3BL / XU7AGA - http://vk3bl.wordpress.com
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