Calibration of 100 Watt PA Generates Gain Values that are Very...

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Calibration of 100 Watt PA Generates Gain Values that are Very...


Calibration of 100 Watt PA Generates Gain Values that are Very Different than the Original Gain Test Provided by FlexRadio -Or-RF Output Becomes Uncharacteristically High For No Apparent Reason

  System Dependencies
  Minimum PowerSDR Version:     1.6.0  
  Applicable Hardware:     SDR-1000 

Content provided by: Tim, W4TME

Problem Description:
There is an important relationship between the output of the sound card and the RF power output. The proper output gain from the sound card is necessary for operating the SDR-1000 with the 100 watt Power Amp (PA).

It is good amateur radio practice to monitor your RF output when operating. If you notice that for some unknown reason (no changes made to the system) the RF output power is not what you expect it (especially too high of power), then you need to find out what the cause is. One step in this process would be to re-calibrate the PA Calibration test.

When you receive your Flex-Radio SDR-1000 that has the 100 watt P.A. installed, you received the results from the PA Gain Test performed as part of the QC process. These results indicate the gain value in dB for each band. It is recommended that once you have your SDR-1000 setup in your shack, that you perform the PA Calibration test your self by transmitting into a dummy load.

The results you receive from your PA Calibration test results should be very close to the results received with your radio or from previous PA Calibration tests where the radio was known to work correctly. The values should you receive should be about ± 6 dB from the ones listed in the Flex-Radio Gain Test. The average value is about 48.0 dB.

If the values are not within specification, then you must find out what is causing the problem so that you possibly do not damage the 100 Watt PA.

Possible Cause of the Problem:
The primary cause of this problem is that the sound card levels are not set correctly. There are some applications that when run on you computer will change the gain values of the sound card without your knowledge. Too much audio gain can overdrive the PA beyond the point of linearity. Too little gain will result in lower than expected RF output.

Problem Resolution:
If you are using the highly recommended M-Audio Delta 44 or PreSonus FireBox sound cards, then make sure that the audio output and input gain values are properly for the sound card’s inputs and outputs.

Refer to the Delta 44 Quick Start Guide for the correct settings for the Delta 44. Use the profile feature in the M-Audio Delta Control Panel to save these setting specifically for the Delta 44 so that can be quickly restored if they are accidentally changed manually or by another application.

Refer to the FireBox Quick Start Guide for the correct settings for the FireBox.

If you are using an unsupported sound card, please refer to the section labeled Automatic Amplifier Gain Calibration in the SDR-1000 Operating Manual for the sound card calibration procedures.


This KB article may reference additional files that are available on the FlexRadio Systems web site Downloads page. Please use the URL(s) below to download the referenced materials.

An Adobe Acrobat Reader may be required to open the file. You can download Adobe Acrobat from here.

KB Source Document(s):

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Last Modified:Monday, August 4, 2008
Last Modified By: Administrator
Type: FIX
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