Re: Spurs and Harmonics - Definitions and Measurements
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Bruce, K4TQL
Small point...the FCC monitors would be testing received RF.? This may be via a remote monitoring
station or from a van parked down the street from your house.? This means that the full system,
including ATU and antenna will be present in signal analysis.? Most discussions fail to include
filtering effects of these components that are external to your transceiver (some designs are better
than others).? This lends credibility to having another ham who is some distance from your location
perform tests to see how pure your signal might be. ?
Testing in an anechoic chamber is the way equipment is tested for type approval or in case of
legal proceedings.?
Arv? K7HKL
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On Mon, Mar 11, 2019 at 7:44 AM BruceN < k4tql@...> wrote: I've seen many messages relating to the cures for spurs and harmonics for the V3, V4 and V5 units.? Right now there are nearly 1000 messages dealing with this topic.? But, I'm confused.? And, what exactly are the limits for emission of spurs and harmonics?? I've researched the FCC regs and it's like reading a foreign language to me.? But what I did glean is that the FCC tests in, basically, an anechoic (to RF) chamber and report the results, depending on frequency range, in microvolts.
What I see in the messages is that folks are reporting spur and harmonic levels in dB.? Now, db is a ratio so what are those db values compared to?? To the level of the primary signal?? Are they measuring spur and harmonic suppression?? Again, compared to what??
If spurs and harmonics readings are to be given as a particular level, they should be reported as dBm, not dB.? dBm is also a ratio but it is compared to a fixed level of 1 milliwatt.? The emitted power given in those units would be the same if measured on a transmitter running 10 watts as a transmitter running 100 watts.
However, if the readings are given in dB, it is representing suppression.? A -50 dB reading on a 10 watt transmitter will have an actual radiated power far less than a -50 dB reading on a 100 watt transmitter.? So, if we're measuring and reporting dB on the uBitx, maybe those reported levels are not so bad as folks think.? The radiated power level would be far less than other signals out there.? Easily seen on a scope with high gain but maybe not readable a mile away or even 3 feet away.
If you are measuring actual output power of the spurs and harmonics, report your readings in dBm.? And if that is the units being used, the uBitx might need some help.
So which is it?
My nickel (2 cents inflated).
Bruce, K4TQL
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