How best to set RTTY drive level

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  • Updated 4 years ago

Running a 6300 with SmartSDR.  My amplifier needs about 40 watts of drive for RTTY. There seem to be two ways to set drive to this level and I wonder which is best.  1. Set DAX TX drive high and back off the TX power, or 2. Set TX power to max and back off DAX TX drive. Either method works, but is one preferable? Or does it matter? My main concern is IMD and distortion.  Thanks.

73, Bill W6WRT


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Bill Turner

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Posted 4 years ago

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Joseph Duerbusch

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Good question Bill.  I set DAX TX to drive high, just a little below full, and then I set the RF Power to drive the amp.  I set mine to abut 25 Watts to get 600 watts out of the Amp (TT Centurion).  I would run it more if I had a HIGH Power amp like you. hi hi

btw, is this the solid state amp you just bought??

Joe K0BX
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Joseph Duerbusch

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Fine Bill.  I think a lot of us really want to know how the SPE 2K-FA amplifier works for use in a RTTY contest.  I am thinking about replacing my old amp for a solid state one.

Joe K0BX
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Bill Turner

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Frankly, I  am a little disappointed in the 2K-FA for RTTY contesting. I worked the Ukraine RTTY contest this weekend and in terms of power and duty cycle it did not perform quite as well as advertised. At 1500 watts it faulted in about two seconds. At 1200 watts it faulted after about of minute of CQing. Only when I kept the output to about 800 watts or less did it operate continuously. This amp has a lot of headroom  - it's rated at 2.4 kW PEP - but cooling is the  problem. For an amp this expensive and not limited by headroom, the designers should have done a better job of cooling. Of course, that's easy for me to say. :-)

This was used when I got it and in all fairness I have not yet cleaned out the air filter or blown out dust from inside, so that may improve things a bit. We'll see.

This is off topic for this group so anyone interested can email me in a few days and I will be glad to continue the conversation on the 2K-FA.

73, Bill W6WRT     dezrat@outlook.com


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Sergey, R5AU

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Bill, I am working well with my 2k- fa, as mentioned into the manual , however for DIGI I keep power at MAX but reducing the level for 1,3k output and run continuously without issues and setup ALC with zero by reducing the driver level.
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Bill Turner

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I think I have been a little too critical of my 2K-FA. After talking to Bob at Expert Linears about the power issue, he believes the amp has a problem, most likely a burned resistor in the combiner. He says it should put out 1200 watts RTTY continuously with no problem. I am going to send it in for repair and we'll see.

73, Bill W6WRT


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Sergey, R5AU

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Bill, you should control  ALC also (zero level) and do not forget Flex6000 HW manual article  7.13,  2K-FA producing up to -12v, divider should be in use.
 You know i am appreciate to keep full power for Amp with full voltage on transistors  - better linear characteristics and higher level of the ALC threshold what also under control with Epxert protection circuit on board
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Tim - W4TME, Customer Experience Manager

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Bill - either method will work fine for best IMD.

I personally leave the power level at the max (100) and adjust the DAX TX gain to a lower value until I achieve the output power level appropriate for the digital mode being used.
(Edited)