Monday, November 28, 2011

Baofeng UV-3R: Second Harmonic Issue

December's QST has a Technical Correspondence (Boafeng UV-3R 2M/70cm Handheld Transceiver) article about the second harmonic issue in the Baofeng UV-3R. Bob Allison, WB1GCM (ARRL Lab Test Engineer), used an HP-8563E spectrum analyzer to determine if the radio meets the standards of FCC Part 97 for spurious transmissions. Bob finds that the radio (two units tested) failed to meet the standards and that "to legally transmit with these radios in the 2 m band, you would have to add a second harmonic low-pass filter at the antenna jack."

First, if you don't understand the basics of a spurious transmission on the harmonic, Steve (K9DCI) provides a good analogy on the of UV-3R Yahoo Group discussion on this topic:
"Spurious signals are more like driving with a 10 foot long beam sticking out the side of the car. As long as you drive on desert roads, you can relax because you "probably" won't whack any hitchhikers in the back of the head."
Some time ago, I had noted the spurious emission problem and posted a link to the mod to fix it on my UV-3R page. And I had thought the issue might have been fixed in newly manufactured radios, since the UV-3R had gotten FCC Type 90 Acceptance. For a major information dump on the topic, I would start with this UV-3R Yahoo Group post - also from Steve (K9DCI). Grant, ZL2BK, documents the magnitude of the problem at various frequencies. Basically, the filtering is better as frequency increases.

It is the issue that will not die on the UV-3R Yahoo Group:
As you can see in the above links, it does not appear that the issue was resolved in the Mark II. Some speculate that it is a quality control issue, but I am more inclined to think it is a limitation built into the design/components of the UV-3R. G4TUP suggests that Vero Telecom (and the various resellers) do not care as they designed the radio for the commercial market and, at the higher frequencies, it works within the standards. To keep the waters muddied, Bob (GM4CID) reports that Vero Telecom claims to have fixed the issue. And Andy (G0FTD) found that hisYaesu VX7R is worse than an unmodded UV-3R.

Here is the link to the low-pass filter mod that shows you how to add a 0805 size 33pF capacitor to reduce the emissions on the second harmonic.

Oh, and because I am apparently a sadist, here is a follow-up link where the same mod was performed and the results were less successful.


  1. WOW! Is this my 15 minutes of fame?

    73, Steve, K9DCI

    1. Yes, you have been immortalized in the UV-3R hall of fame!