[G0HZU_JMR]

I've got various Noisecom (diode based) noise sources here and I think they all show a slight increase in noise level if I reduce the reverse voltage slightly. I use this feature as a fine tune when setting the noise source via a 1dB step attenuator. When I use these noise sources for a critical task I have to set the reverse voltage accurately using a decent DMM to get it set to 28.00V.

Getting back to the Mutek debate, I dug out a DSP based SINAD meter today and measured the Mutek mk1 FT290R on FM. This DSP based SINAD meter has an ultra sharp AF notch and it is just a few Hz wide. I've done various tests on it over the years using a noise source and a precision step attenuator to prove how accurate it is.

This test method means using a sig gen set to a 1kHz test tone with 3.5kHz deviation. I tried three sig gens and they all agreed very closely in the following test.

The spec for a stock mk1 FT290R in FM mode is 0.25uV PD for 12dB SINAD and my Mutek FT290R managed 0.145uV PD for 12dB SINAD in FM mode. So there is a definite improvement compared to the spec at least. Note that I didn't select any SINAD AF bandpass filter options in the SINAD meter and left the meter filtering to 'flat'.

When testing in SSB mode, I'm not sure when the AGC kicks in on the Mutek 290R but I think it is still some way off from the levels generated by my noise sources. I think any AGC or compression that kicks in with the noise source turned on will make the noise figure appear slightly worse when done with the method that I use.