Jan 30 2013

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:

Scanner-Forum

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:

UV-5R-VHF

VHF: 56 dBm Down

UV-5R-UHF

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.

8 comments on “Baofeng UV-5R Spectrum Analysis Revisited”

  2. 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.

  3. 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.

  4. A ham friend of mine claims you can do this: Tune one Chinese Cheapie Radio to 146 MHz, and radio #2 to 438 MHz (or 3X Radio #1 freq). You don’t just get EMI, you get full-on multi-band emission. Be sure volume on radio #2 is not up too high, or you will get huge feedback.

  5. Hi there
    I use this “property” of my UV-5R (and of any TX) to check my 23cm transverter under construction. The transverter conversion is 144 = 1296, so if I transmit in, let say 432, using the third harmonic would be 1296, but you be aware that it is 3 times the “base receiver” (Ts-2000) frequency, so one should check other frequencies, let say 1295, now the “base receiver” should be at 143Mhz, to be heard by the transverter the UV-5R should be tx at 431.667, but this frequency divided by 3 is 889Khz apart of that on the “base receiver”. This “property”; as I said before, is in this case welcome when you don’t have a Rf signal generator at hand……………

    Al
    CX land

Comments are closed.