Testing the Harmonics of a Baofeng BF-F8HP

Written on August 31, 2018

I’ve heard that Baofeng HTs have poor harmonic suppression on several ham radio forums, so I decided to test it for myself with the Baofeng BF-F8HP I bought on Amazon. The BF-F8HP is a 2 meters and 70 centimeters HT with 1, 5, or 8 W output power. When a radio transmits, harmonic waves at multiples of the transmitted frequency are created, which must be suppressed before transmission.

In this test, I transmitted on about 150 MHz, so I looked for harmonics at N*150 MHz: 300, 450, 600, 750, and 900 MHz. I used a 30dB attenuator to protect the spectrum analyzer, an HP 8555A.

The Test Setup

To generate the spectral displays below, I keyed the transmitter without speaking into it. The spectrum is mostly just the FM carrier. All images use the top edge of the screen, 0 dB, as the reference for power relative to the fundamental, shown below.

The Fundamental

The second harmonic is roughly 54 dB down, which is pretty good.

2nd Harmonic

The third harmonic is at -44 dB, so that’s not the greatest.

3rd Harmonic

Fourth harmonic: -56 dB.

4th Harmonic

Fifth harmonic: also -56 dB.

5th Harmonic

Sixth harmonic: at or below the noise floor.

6th Harmonic

The mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency between 30-225 MHz must be at least 60 dB below the mean power of the fundamental. For a transmitter having a mean power of 25 W or less, the mean power of any spurious emission supplied to the antenna transmission line must not exceed 25 µW and must be at least 40 dB below the mean power of the fundamental emission, but need not be reduced below the power of 10 µW. A transmitter built before April 15, 1977, or first marketed before January 1, 1978, is exempt from this requirement.

FCC Part 97.307(e)

I’m not a lawyer, but here’s my reading of the law:

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# for transmitters 30-225 MHz
if meanPower <= 25 W:
    maxSpuriousEmissions = 40 dB
else:
    maxSpuriousEmissions = 60 dB

By this reading, my Baofeng passes the emission standards… barely. I’d love to have all harmonics 60 dB below the fundamental, which would mean it passes the emissions standards for sure.

As a bonus, here’s what the FM modulated waveform looks like in the frequency domain, more zoomed in. I’m saying “AHHHHH” into the microphone for this.

modulated zoomed modulated