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uBITX v5 TX IMD measurements #ubitx #two-tone #v5

Doug Hall
 

All,

I just finished measuring the two-tone TX IMD on my v5 uBITX. These are 3rd order products, and I measured relative to either tone. Since the ARRL states their measurements relative to PEP I have included that as well, for those who sleep better at night secure in the belief that their radio is clean :-)

This is at 10W PEP using 700 and 1900 Hz tones. My radio puts out 10W from 80 through 20 meters, and falls off to 5W on 10M:

80m -25.5 dBc (-31.5 dB PEP)
60m -22.5 dBc (-28.5 dB PEP)
40m -22.0 dBc (-28.0 dB PEP)
20m -24.5 dBc (-30.5 dB PEP)
17m -21.0 dBc (-27.0 dB PEP)
12m -25.5 dBc (-31.5 dB PEP)
10m -22.0 dBc (-28.0 dB PEP)

As my flight instructor used to say after one of my landings, "I've seen worse, but I've seen a lot better." This is probably not atypical of IRF510s.

Now I'm going to hook up the 'scope and look at the CW waveform.

73,
Doug K4DSP

Ashhar Farhan
 

Interesting,
Now a days, the TX IMD is the most critical parameter on SSB mode. Consider the best on class IMD (called Splatter by the old timers), it is about -35 dbc. Thus, this is what you will hear on the opposite side band. On the other hand, claiming a -60 db opposite side band suppression is useless : you are subsitituting the other sideband with splatter. 
Now, consider a receiver trying to receive an S 5 level signal adjacent to an S9+10 db signal. However good your receiver is, the splatter of the loud signal is going to ruin your reception.
Much appreciate the measurements. What is your measurement setup?

73, f

On Sun 4 Aug, 2019, 5:04 AM Doug Hall, <k4dsp.doug@...> wrote:
All,

I just finished measuring the two-tone TX IMD on my v5 uBITX. These are 3rd order products, and I measured relative to either tone. Since the ARRL states their measurements relative to PEP I have included that as well, for those who sleep better at night secure in the belief that their radio is clean :-)

This is at 10W PEP using 700 and 1900 Hz tones. My radio puts out 10W from 80 through 20 meters, and falls off to 5W on 10M:

80m -25.5 dBc (-31.5 dB PEP)
60m -22.5 dBc (-28.5 dB PEP)
40m -22.0 dBc (-28.0 dB PEP)
20m -24.5 dBc (-30.5 dB PEP)
17m -21.0 dBc (-27.0 dB PEP)
12m -25.5 dBc (-31.5 dB PEP)
10m -22.0 dBc (-28.0 dB PEP)

As my flight instructor used to say after one of my landings, "I've seen worse, but I've seen a lot better." This is probably not atypical of IRF510s.

Now I'm going to hook up the 'scope and look at the CW waveform.

73,
Doug K4DSP

Doug Hall
 

On Sat, Aug 3, 2019 at 08:34 PM, Ashhar Farhan wrote:
Much appreciate the measurements. What is your measurement setup?
 
I used my laptop and the Audacity application to generate the 700/1900 Hz two-tone signal. This was fed from the laptop audio output through a variable attenuator with a 10-turn pot.  This feeds the mic jack and prevents overdriving the uBITX mic amplifier. The uBITX RF output goes to a dummy load with a 60 dB attenuator output. The attenuated output goes to a Rigol DSA-815 spectrum analyzer, and that is used for the IMD measurements.

The uBITX has been a very enjoyable project.

73,
Doug K4DSP

Gordon Gibby
 

Thank you so much for making those measurements!   Better than I would’ve expected and your power output data is also very interesting, I’ll have to save up for a version five.  




On Aug 4, 2019, at 00:00, Doug Hall <k4dsp.doug@...> wrote:

On Sat, Aug 3, 2019 at 08:34 PM, Ashhar Farhan wrote:
Much appreciate the measurements. What is your measurement setup?
 
I used my laptop and the Audacity application to generate the 700/1900 Hz two-tone signal. This was fed from the laptop audio output through a variable attenuator with a 10-turn pot.  This feeds the mic jack and prevents overdriving the uBITX mic amplifier. The uBITX RF output goes to a dummy load with a 60 dB attenuator output. The attenuated output goes to a Rigol DSA-815 spectrum analyzer, and that is used for the IMD measurements.

The uBITX has been a very enjoyable project.

73,
Doug K4DSP