Source for TX spectrum display?

Bill Turner

Where in the transmitter is the source for the spectrum display?  Is it the actual output on-the-air signal oris it taken from an earlier stage?  Running SSDR 1.11.12 with 6300.

James Whiteway

I imagine it's from the ADC and then the FPGA. There is a diagram somewhere showing the signal path in a 6000 Series radio. (Block diagram) There are some youtube videos I believe, as well from some of FRS's engineers explaining some of the proccessing that takes place too. James WD5GWY

Tim - W4TME

James, your answer is correct!  We have a winner! 

This is the 6700 block diagram, but it is the same principle in all of the 6000s.

Steve-N5AC

The transmit spectrum is never displayed directly in SmartSDR.  We discussed doing this early on, but decided against this, preferring rather to display it simply as received through the receive chain via coupling in the radio itself.  This generally works very well and gives you a good display without "cheating" and showing what we hope goes on the air from the transmitter using something before the PA.  So if there is a PA issue in your radio, you will be able to see this in the spectrum.  The only issue with this method is that at higher frequencies, there are some spurs that are visible in the receive spectrum that are not transmitted and to not appear on the air.  So it should be taken as representative, generally, with this exception.