Example Of Spurious Emissions

A recent discussion on the Amateur Radio subreddit addresses the spectral purity of one reader’s Quansheng TG-UV2 HT.

This HT was connected to a IFR Systems AN920 Spectrum Analyzer (view full size image.)

Each one of the bars you see on the graph represents a spurious emission that the radio is transmitting. I wish I had thought to take a photo of a compliant radio. I did not think to do that. Perhaps KD8TWG has a photo of a compliant radio to post? We tested quite a few radios that were compliant without any appreciable spurs.

The bar on the far left of the screen represents the desired emission on the fundamental frequency. I believe we tested at 146.55 MHz? Each one of the other bars represents a spurious emission on another frequency. The higher the bar, the stronger the emission. A good radio should only see the single bar on the left side at the fundamental, and no other bars. As all the other emissions are suppressed by the filters.

I purchased one radio Quansheng and tested one radio Quansheng. (we tested a large variety of radios and brands on Sunday) Certainly not a comprehensive test of Quansheng! It’s probably not appropriate to condemn the entire brand over one test. I would encourage everyone to test their radios and post the results. Please make sure the frequency range of the Spectrum Analyzer is at least past the 3rd harmonic (440 MHz). Ideally it should scan up around 1200 MHz (1.2 GHz). I’ve seen some people try to “cheat” the test by only scanning for spurs 10 MHz around the fundamental. Also make sure we can see the noise floor in the test.

Some have commented about testing with the OEM antenna attached. Part 97 clearly states this is not acceptable. You have to connect directly to the Spectrum Analyzer.[1]

The results of this test led the owner of the radio to conclude that it was not compliant with Part 97 and, therefore, not legal to use for Amateur Radio.

Part 97 Subpart D Section 97.307(e) states: “The mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency between 30-225 MHz must be at least 60 dB below the mean power of the fundamental. For a transmitter having a mean power of 25 W or less, the mean power of any spurious emission supplied to the antenna transmission line must not exceed 25 µW and must be at least 40 dB below the mean power of the fundamental emission, but need not be reduced below the power of 10 uW.”[2]

Regardless of whether or not the conclusions in this case are correct, as licensed Amateur Radio operators we are individually responsible for ensuring that our equipment complies with the spectral purity requirements of Part 97.

Is your radio in compliance?

Footnotes

[1] “Experience with Quansheng: not legal for Amateur Radio”, Reddit, accessed November 15 2016, https://www.reddit.com/r/amateurradio/comments/5d2q2o/experience_with_quansheng_not_legal_for_amateur/da1cbqv/.

[2] “Part 97 - Rules of the Amateur Radio Service”, ARRL The national association for Amateur Radio, accessed November 15 2016, http://www.arrl.org/part-97-text.