6500 Transmit Anomaly

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  • Updated 4 years ago
I was operating JT-65 on 15M today. Had the RF Power slider set to 25 and was getting 22 watts indicated on my LP-100A watt meter.

Went to lunch for two hours and left the rig on. When I got back I worked a station on JT-65 (still on 15M) and indicated power output on my LP-100A was only 0.5 watt. I did not change any of the sliders... All five JT-65 transmissions for this contact indicated 0.5 watts, but the PA temp (as indicated by DDUtil) went up much faster than it does when I'm actually outputting 25 watts. In fact, it went up as if I had power output set to 100 watts even though the external wattmeter was still showing only 0.5 watts of actual output.

After this happened, I switched bands and then came back to 15M and with the same SmartSDR settings indicated power output was back to ~22 watts on JT-65.

Anyone seen this? This this a known issue? I have not been able to reproduce it.

One other thing I've noticed on transmit is SWR indicated on SmartSDR's transmit panel. It seems to indicate an SWR lower than it actually is. On 20M, my SWR is 1.3:1 (as indicated on my LP-100A), but SmartSDR displays it as 1:1. On 15M, it's 1.54:1 (LP-100A), yet SSDR displays it as 1.2:1. I have the internal ATU in bypass mode and no external tuner in the line.
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Jerry Gardner

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Posted 5 years ago

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George Molnar, KF2T, Elmer

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Can't speak to the power issue, but the SWR readings being different probably comes from the fact that you're measuring at two locations on the feeder - where the rig samples vs where your external bridge does. Unless you're looking at a perfect termination and line, some variation is expected and normal.
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Jerry Gardner

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Hmmm. I wouldn't expect the 3 feet of RG-214 between the 6500 and LP-100A's sampler to make that much of a difference.
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John W9KXQ

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Jerry,
In a conversation with Dudley from Flexradio recently, he advised me that it was better on the RF amp part of the Flex (I have the 6500 ) if you just reduce the drive level (DAX) and leave the RF power control alone.  Since that conversation, when I use the digital modes, I have followed his instructions without any RF Power problems.

John
W9KXQ
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jim WB5AAA

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so Jerry   where do u set the RF power  in smartSDR ?
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Jerry Gardner

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For JT-65 I've been setting power by setting the RF Power slider in SmartSDR to 25 and the TX Gain slider in the DAX control panel to 40. This gives about 22 watts output as measured on my LP-100A watt meter. This method puts the "peak" bar in the SmartSDR Level indicator at just a hair below 0 dB.

I've also tried the method John suggests above: leaving the SmartSDR RF Power slider at 100 and adjusting the power output using the TX Gain slider in the DAX control panel. The problem with this method is that the TX Gain slider is very non-linear in this mode. Power doesn't even start to drop below 100 watts until I pull the TX Gain slider down to around 17, and then everything between 0 watts and 100 watts is compressed between 0 and 17 on the slider and is very sensitive to any movement.
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Jerry Gardner

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Here's another transmit-related thing I just noticed: when clicking on the Tune button the rig slowly ramps up to something close to what Tune Power is set to, taking about 1-1/2 seconds to get to full output. My LP-100A meter increments like a counter.

Is this normal behavior for the Tune function?
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Tom--W4FAS

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Tom Tucker

I have experienced this same delay in ramping up to the set for transmit power. It does not matter if the set power is 25w, 50w, or 100w. The first transmission of  the day takes the longest to ramp up(about 10 seconds). I have never got anything but very good signal reports. I have never had a station indicate I started out weak but than got stronger. If I make back to back transmissions there is no delay. If I have several minutes between transmissions then delay or ramp up starts to creep back in.

I experience the delay no matter which method I use to set the power. The ammeter on my power supply and the rf output meter on my external antenna tuner both indicate a ramp up is occurring. I put the external ant. tuner in line just to see what it's rf output meter would show. Both the external ant. tuner and the flex-6500 ant. tuner are in the bypass mode. 

Any recommendations? 

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Jerry Gardner

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I have further noted that the gradual ramp-up when hitting the Tune button only happens once, the very first time I do it. Doing it again causes the power to instantly go to the level set in the Transmit tab of the main Settings menu.