It's a square wave, all the way up to 300MHz. It uses the 3rd and 5th harmonics to get to higher frequencies. For example, a 200MHz square wave is used for 200MHz, 600MHz and 1GHz. The power level for the 3rd harmonic is about 10dB lower than the fundamental, and the 5th harmonic is about 20dB down from the fundamental.
The newer nanoVNA V2 SAA-2N also has a squarewave output but since it's oscillator sweeps right up past 3GHz on the fundamental, the output is able to produce even sharper squarewaves right up into the UHF-VHF region. Measured on an old 0-500MHz analog spectrum analyser, the harmonics are very noticable across the whole frequency range. There are significant even-order harmonics too! With output set to 52MHz, 3,5,7,9 harmonics are = -9, -15, -21, -23dBm (relative to fundamental, fairly close to theoretical levels) Even order are also fairly strong x2,4,6,8,10 are = -33, -35, -37, -39, -41dBm (there are no even harmonics in perfect square waves). This is one reason why these VNAs perform very poorly as spectrum analyzers, and maybe why the range of return loss measurements is fairly limited. For it's intended purpose though, I'd argue that the performance/price ratio is still far better than a $100,000 instrument :-)
I was messing around with one of my NANO's and tried to use it as a very crude Spectrum Analyzer and was surprised that it worked as well as it did! The signals on your scope is limited to low BW, that's why you cant see what the signal really looks like above 20MHz. TNX 4 the upload! 73 N8AUM
At 927.500, my H4 outputs +1.26 dBm. At 450.000, it outputs +1.22dBm At 400.000, it outputs +1.18dBm. All in all across the bands tested, minimum output level was +1.14dBm. Pretty flat across the bands tested. Some noise on several signals tested, especially over 530 MHz. At 147.000, output changed slightly from wide to narrow, but not enough to cause concern. Harmonic generation shows a lot of ringing, which appears to be a normal function of using harmonics to generate a signal. I am just a little amazed at the output being so steady. My next test, will be with the NANO VNA-F. My favorite of the two, and far easier to update as well.
It's a square wave, all the way up to 300MHz. It uses the 3rd and 5th harmonics to get to higher frequencies. For example, a 200MHz square wave is used for 200MHz, 600MHz and 1GHz. The power level for the 3rd harmonic is about 10dB lower than the fundamental, and the 5th harmonic is about 20dB down from the fundamental.
The newer nanoVNA V2 SAA-2N also has a squarewave output but since it's oscillator sweeps right up past 3GHz on the fundamental, the output is able to produce even sharper squarewaves right up into the UHF-VHF region. Measured on an old 0-500MHz analog spectrum analyser, the harmonics are very noticable across the whole frequency range. There are significant even-order harmonics too!
With output set to 52MHz, 3,5,7,9 harmonics are = -9, -15, -21, -23dBm (relative to fundamental, fairly close to theoretical levels)
Even order are also fairly strong x2,4,6,8,10 are = -33, -35, -37, -39, -41dBm (there are no even harmonics in perfect square waves).
This is one reason why these VNAs perform very poorly as spectrum analyzers, and maybe why the range of return loss measurements is fairly limited.
For it's intended purpose though, I'd argue that the performance/price ratio is still far better than a $100,000 instrument :-)
I was messing around with one of my NANO's and tried to use it as a very crude Spectrum Analyzer and was surprised that it worked as well as it did! The signals on your scope is limited to low BW, that's why you cant see what the signal really looks like above 20MHz. TNX 4 the upload!
73 N8AUM
At 927.500, my H4 outputs +1.26 dBm.
At 450.000, it outputs +1.22dBm
At 400.000, it outputs +1.18dBm.
All in all across the bands tested, minimum output level was +1.14dBm.
Pretty flat across the bands tested.
Some noise on several signals tested, especially over 530 MHz.
At 147.000, output changed slightly from wide to narrow, but not enough to cause concern.
Harmonic generation shows a lot of ringing, which appears to be a normal function of using harmonics to generate a signal.
I am just a little amazed at the output being so steady.
My next test, will be with the NANO VNA-F.
My favorite of the two, and far easier to update as well.
what instrument did you measure with? if a power meter, it integrates all the harmonics so would stay constant.
Well, shouldn't the 50 Ohm pass-through terminator be rather located at the scope side of the cable, for proper termination of the cable?
9:25
Yep, I think I’d better put the load at far end of coax near the oscilloscope.
Can i connect the vna output to an oscilloscope to see the waveform?
yes: 7:00
You get what you pay for!