Baofeng UV-5R Spectrum Analysis Revisited
A few days ago I noticed some incoming traffic from a Dutch scanner forum. I could read there without registering, which made life easy. The link provided there was about the Baofeng UV-B5 review, but I also noticed something else interesting in the thread.
One of the forum members did some measurements on the UV-5R, stating that the radio was totally crap due to excessive spurious emissions and harmonics. He added a screen shot of his Rigol spectrum analyzer, probably the same model I own. This was what he came up with:
If this were correct, the Baofeng UV-5R would be the most horrible design ever. But wait, we did this already a long time ago, and the UV-5R wasn’t too bad at all. All of his bothered me enough to pick up a few of my own UV-5R’s and repeat the measurements. I tried the oldest one I have (BFB231), and a more recent one (BFB239). Results didn’t differ in any way, so I just picked one. These were the results:
VHF: 56 dBm Down
UHF: 54 dBm Down
So, what’s happening here?
I considered a few possibilities:
1) his UV-5R was a dud,
2) he made errors while measuring.
The answer is likely #2. The only way I could replicate his results was by reducing external attenuation to such a low level that the linearity of the spectrum analyzer was compromised.
Higher order harmonics
I’m pretty sure his faulty results were caused by a well-known factor: distortion due to higher order harmonics. When the input signal level you feed into a spectrum analyzer is (too) high, spurious images of the input signal harmonics are generated due to the non-linearity of the mixer conversion. It’s kinda like LSD to a junk; you start seeing things which aren’t there.
Bottom line: it’s easy to make any HT look bad by not understanding the test equipment you’re working with.
Nice explaining about the measurement error / technology. Thnks.
The explanation was most excellent. As a ham that never got close enough to touch a analyzer it was most appreciated. I did see something that I have questions about. Please remember that I know nothing about analyzers. I did notice that his indicated Center Frequency of 350.000, whereas yours showed Marker 869.0000 and 289.936085. Whats the difference? How did you get yours to be on 869.00 when the highest it will go is 500.-/+. I have one with BFB251 and enjoy it. Just go to change out the antenna.
It’s not about hoe high the HT goes in frequency, but the strength of signals the radio emits outside the frequency range. In my second example the UV-5R was transmitting on 434.50 (the first peak at the left), the second peak shows what is left of the signal at the second harmonic frequency (869MHz).
To prevent interference, these secondary (and third, if present) harmonics should be as low as possible. In an ideal situation, these should be no secondary peak at all. See here for more info on harmonics.
I performed the measurement on the UV-5R with the result above. Used a 40 dB attenuator, so that results in about -3 dBm to the spectrum analyzer. The UHF spectrum on high power looked fine, as did the VHF spectrum on low power. So I would go for option 1 instead of 2: my UV-5R was a dud.
Noted! Pleased to meet you BTW.