So if my math is right, if you are on HF running a $10 dollar 50 mW xmitter you are required to filter the harmonics down to single microwatts. But if you're running a $7,000 dollar 1,500 watt commercial linear the FCC says you can legally radiate stronger harmonics than the total transmitter output of the ham with the $10 dollar 50 mW xmitter.
Good demo of using SA to find transmitters with inadequate filtering. Adding filters is not a problem at all and is not that expensive. Also, 14 MHz harmonic would be called the 2nd harmonic. You had referred to it at times as both the first harmonic and the 2nd harmonic. Confusing! It is the "first harmonic" but it is not called that, it is called 2nd harmonic, then 3rd etc... Based on 2x freq, 3x freq etc... New comers will be confused by this for sure.
Again a good demonstration of measurement of RF output with the harmonics in a qrp Tx on the SA. As it turns out the 3 pole pi (Chebychev's..!?) filter is not sufficient. The same low pass filter is being used in the Rx mode too, I think. In that case the insertion loss, this 3 pole filter might introduce may be measured. Obviously a 5 pole filter would introduce more attenuation to the incoming signal on Rx mode. So, the 3 pole configuration is a compromise. The magnitude of the the spurious signals after the TX (TRX) has been hooked up to a good antenna system shall be measured at a distance; the TRX must be in a good metallic enclosure assuring a proper screening.
As the law gives not a penny on the antenna characteristics it still will be illegal to use the transmitter, even if the antenna (magically?) would filter out the harmonics. BUT: Bear in mind, most antennas that are in resonance at 7MHz will also be at least half-decent in transmitting/receiving on 14 MHz or on 21 MHz or on 28 MHz as it will be multiple of the basic wave-length on these frequencies!, so how could it filter out the 2nd harmonic? Quarter-Lambda will become Lambda-halfes, Lambda-halfes would become lambda-length which all could also be used for transmission, for example.
@@Slartibartfas042 I think you have misunderstood the suggestion I made at the end. I, initially accepted the need of additional filtering at the output. And it can be and is always accomplished in transmitters without any doubt. When the populated board without screen is hooked up to the SA there's a chance that it maybe picking up stray signals that escaped filtering. And finally a good resonant antenna is a series tuned circuit with high Q that certainly offers an impedance match for maximum power transfer.
note that what that law says means the TOTAL spurious emission must be 43dB below your fundamental. i.e. the total power minus the fundamental must be 43dB down. Practically, however, that spurious emission is dominated heavily by the second harmonic in your case because the third one was like some 20+ dB below the second,
Harmonics are easy to suppress as they increase in frequency from the main signal, and the power is easily cleared up with better board designs, less loading on the output network.
I am bit confused here. Isn't the HP 8591 displaying voltage in dBm, not power? Wouldn't the difference of 20.7 dBm between fundamental and 2nd harmonic at 50 ohms be equivalent to a 41.4 dB below the fundamental's power? So isn't it within a hair of meeting Part 97.307?
So if my math is right, if you are on HF running a $10 dollar 50 mW xmitter you are required to filter the harmonics down to single microwatts. But if you're running a $7,000 dollar 1,500 watt commercial linear the FCC says you can legally radiate stronger harmonics than the total transmitter output of the ham with the $10 dollar 50 mW xmitter.
Believe it or not, 7 MHz is officially considered to be the 'first harmonic' of 7 MHz. Fourteen MHz is the 2nd.
Good demo of using SA to find transmitters with inadequate filtering. Adding filters is not a problem at all and is not that expensive. Also, 14 MHz harmonic would be called the 2nd harmonic. You had referred to it at times as both the first harmonic and the 2nd harmonic. Confusing! It is the "first harmonic" but it is not called that, it is called 2nd harmonic, then 3rd etc... Based on 2x freq, 3x freq etc... New comers will be confused by this for sure.
Against the rules, there are no laws.
The Pi Network does also impedance matching
Again a good demonstration of measurement of RF output with the harmonics in a qrp Tx on the SA.
As it turns out the 3 pole pi (Chebychev's..!?) filter is not sufficient.
The same low pass filter is being used in the Rx mode too, I think. In that case the insertion loss, this 3 pole filter might introduce may be measured. Obviously a 5 pole filter would introduce more attenuation to the incoming signal on Rx mode.
So, the 3 pole configuration is a compromise.
The magnitude of the the spurious signals after the TX (TRX) has been hooked up to a good antenna system shall be measured at a distance; the TRX must be in a good metallic enclosure assuring a proper screening.
As the law gives not a penny on the antenna characteristics it still will be illegal to use the transmitter, even if the antenna (magically?) would filter out the harmonics. BUT: Bear in mind, most antennas that are in resonance at 7MHz will also be at least half-decent in transmitting/receiving on 14 MHz or on 21 MHz or on 28 MHz as it will be multiple of the basic wave-length on these frequencies!, so how could it filter out the 2nd harmonic? Quarter-Lambda will become Lambda-halfes, Lambda-halfes would become lambda-length which all could also be used for transmission, for example.
@@Slartibartfas042 I think you have misunderstood the suggestion I made at the end.
I, initially accepted the need of additional filtering at the output.
And it can be and is always accomplished in transmitters without any doubt.
When the populated board without screen is hooked up to the SA there's a chance that it maybe picking up stray signals that escaped filtering.
And finally a good resonant antenna is a series tuned circuit with high Q that certainly offers an impedance match for maximum power transfer.
I just purchased one of these kits. Did it come with the schematic and parts list, or do you know where I can get them? Thanks
note that what that law says means the TOTAL spurious emission must be 43dB below your fundamental. i.e. the total power minus the fundamental must be 43dB down. Practically, however, that spurious emission is dominated heavily by the second harmonic in your case because the third one was like some 20+ dB below the second,
I missed the TOTAL part, you are right. the new regulations are very demanding from the past ones
So,,, how does that compute? Another 23 db? I'm new, if you hadn't figured that out.
@@jdmccorful the spec is 43dB for the harmonic. I measured 20dB for my radio. so I need another 23
Harmonics are easy to suppress as they increase in frequency from the main signal, and the power is easily cleared up with better board designs, less loading on the output network.
People must also be aware that FCC rules, are not laws.
Splatter is simply poor operating.
Pi filter and proper circuit loading.
An Idea...build a filter display attenuation at sa...nice video
I am bit confused here. Isn't the HP 8591 displaying voltage in dBm, not power? Wouldn't the difference of 20.7 dBm between fundamental and 2nd harmonic at 50 ohms be equivalent to a 41.4 dB below the fundamental's power? So isn't it within a hair of meeting Part 97.307?
dBm is power. dBm is dB milli-watts
@@IMSAIGuy Ah, so it is.....
so if I was to check a Baofeng for harmonics, spurious I would set center to say 146.52 and the span to say 30mhz???
the harmonics will be 293.04 439.56
I got a pixie kit and didnt knew this was so bad filtered...
fcc wont enforce; drown the bay in electrosmog 73
3rd Harmonic on Baofang transmitting at 146MHz is almost as strong as the fundamental!! SO much for good engineering practice! :)