Mods for cheap FM dual band rig: Baofeng UV-3R
I’ve bought for less of 40eu this little handeld rtx.
It works quite well but needs some mods.
On 70cm all is ok, on 145 MHz the second harmonic is only 20dB down to the carrier…
This is due to large design of output Low Pass Filter to cover the whole band 136-174 MHz, but in my country we can only transmit on FM between 144.5 – 145.8 and the 2nd harmonic on 290MHz can’t be well filtered.
I’ve found on Yahoo Group of UV-3R a simple mod for drop down the second harmonic by adding a single 47pF capacitor.
Another useful mod is decrease the BF audio level, too high by default also at the lowest volume step.
Spectrum before the mod on 145 and 431 MHz (click to enlarge)
Spectrum after the mod on 145 and 431 MHz
As we can see the 2nd harmonic on 145MHz is lowered by about 20dB, reaching the more convenient level of 40dBc, on 70cm no significant change.
Power measured on 145 and 430 MHz
The volume reduction is obtained simply by placing a resistor of 56k above (in parallel) the existing 100k as feedback for audio power amp