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Author Topic: HF Digital - Maximizing my tramsmitter output  (Read 1262 times)
KC9QQM
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Posts: 207




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« on: October 04, 2017, 08:54:02 AM »

I recently got a RigBlaster Advantage and have had a blast with it on JT and FT modes. I have the controls for the audio output on my laptop and on the RigBlaster set to about 50% but what is the best way for me to actually monitor my transmission to see if I am under or over modulating and getting the most bang for my watt as the case may be?

My rig is a Icom 706MKii but I have no other radios to using to listen while I transmit. Could my o-scope be used??

Thanks,

Jeff
KC9QQM
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KC4ZGP
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Posts: 1637




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« Reply #1 on: October 04, 2017, 09:13:58 AM »

Have a person send a snapshot of your water fall.

Ask them if you're overdriving. An overdriven condition looks like stripes on either side of
your signal.

Kraus
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N6YFM
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Posts: 502




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« Reply #2 on: October 04, 2017, 10:55:16 AM »

I recently got a RigBlaster Advantage and have had a blast with it on JT and FT modes. I have the controls for the audio output on my laptop and on the RigBlaster set to about 50% but what is the best way for me to actually monitor my transmission to see if I am under or over modulating and getting the most bang for my watt as the case may be?

My rig is a Icom 706MKii but I have no other radios to using to listen while I transmit. Could my o-scope be used??

Thanks,

Jeff
KC9QQM


#1:   ALC meter is your friend:  Turn up audio drive until you just start to see ALC movement, then back off a slight touch.
You are now driving the maximum amount of audio drive that does not result in ALC foldback, so it should be optimized
and yet clean.  [Note:  PSK31 is VERY sensitive to ANY ALC as it will distort your waveform (Phase shift keying), but JT modes
are very much NOT sensitive to  moderate ALC action, so some amount of indicated ALC on the meter will not harm
JT modes.  Either way, the best answer is to keep any ALC so low that it just barely shows at the meter beginning.]

#2:   Trust but verify:   You can use a station monitor, spectrum analyzer, second SDR receiver, etc, to study
what your transmission looks like.   A nearby friend can also relay this information to you.

Cheers,

Neal
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WA3SKN
Member

Posts: 6497




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« Reply #3 on: October 05, 2017, 05:22:26 AM »

DON'T overdrive the IC706 rig.  The finals are almost impossible to find.
Any signal that triggers the ALC is too high.  Digital likes you to stay in the linear portion of the curve.

-Mike.
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KC4ZGP
Member

Posts: 1637




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« Reply #4 on: October 05, 2017, 05:30:37 AM »


Ten-four to that Mike. Never overdrive. It's impolite.

Kraus
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K6BRN
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Posts: 456




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« Reply #5 on: October 05, 2017, 09:17:08 PM »

Quote
what is the best way for me to actually monitor my transmission to see if I am under or over modulating and getting the most bang for my watt as the case may be?

Quote
Could my o-scope be used??

YES.

An inline RF coupler that provides an attenuated sample of the transmitted RF to a BNC port that can be connected to an oscilloscope, with most of the signal still going to the antenna.  They are not too expensive and quite a few are available.  If you are looking to buy a decent one, go to the Wavenode site and look at their "RF Current Sensor" the CS-1 ($65) - its an inline RF coupler. 

The monitor output from a coupler is usually attenuated by 30-40 db relative to the input signal (-30db means that if you TX 100 watts, the actual signal at the monitor output port will be 100 mW) and can be fed directly into an oscilloscope.

Your oscilloscope should have 50-100 MHz bandwidth.  It will display your TX waveform exactly as it is and will reveal any GROSS distortions.  But subtle distortion is hard to see and can cause "splatter" that is not detectable from the 'scope's waveform display.

So... what is the BEST way to monitor your TX signal quality?  Probably a spectrum analyzer or good station monitor like the LP-700A.  Expect to spend a LOT for the best.

Best Regards,

Brian - K6BRN
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