Baofeng UV-5R Harmonics -30dB

[N4SRN]

I’m doing a Ham refresher class for a local CERT group who got their Tech licenses a decade ago but rarely use radios. I picked up a 4-pack of Baofeng UV-5R radios as demo units and door prizes. While these new production units have FCC stickers, the one I measured with my TinySA today had harmonics -30dB below 146.520 MHz. The FCC standard is -40dB.

In real-world use, is this a real concern on 2m/70cm? If anyone is close enough to hit a 2m/70cm repeater, will that cause problems? More importantly, will it cause issues with nearby police/fire comms?

Bret/N4SRN

 

[techman210]

Congratulations!

It looks like you got some good ones!

Of course, I’m just kidding. Which harmonic? If it was the third, it would fall in the UHF ham radio band.

Did you use any attenuation between the radio and the consumer grade spectrum analyzer? Because just like any other radio, if you hit it with too much power, strange things will happen in the front end.

The real danger of these radios in interfering with another services is if you plug them into an amplifier, and then the harmonics and spurious responses get high enough where they can create harmful interference.

 

[prcguy]

I’m doing a Ham refresher class for a local CERT group who got their Tech licenses a decade ago but rarely use radios. I picked up a 4-pack of Baofeng UV-5R radios as demo units and door prizes. While these new production units have FCC stickers, the one I measured with my TinySA today had harmonics -30dB below 146.520 MHz. The FCC standard is -40dB.

In real-world use, is this a real concern on 2m/70cm? If anyone is close enough to hit a 2m/70cm repeater, will that cause problems? More importantly, will it cause issues with nearby police/fire comms?

Bret/N4SRN

Your not measuring right or your overloading the Tiny SA. Add a good 20dB external attenuation and try again. A bad Baofeng might be 55dB down on the 2nd harmonic but not 30dB.

 

[N4SRN]

I had -30dB of hardware attenuation installed between the radio on Low Power and the Tiny SA - sorry I forgot to mention that! I also set the TinySA for -30dB gain.

When I say -30dB wrt the harmonics, I talking about the difference between the 146.520 MHz peak and the next highest harmonic rather than the absolute values.

While a few of us carry Ham HTs while in service, there’s rarely two of us on a shift carrying an HT, so they’re not much use. As some are not licensed and a few let their licenses lapse, I’ll be pushing for us to use cheap FRS radios. We’re usually all within a few hundred yards of one another when in service at events (elections, parades, etc.)

But if we can get the team to use their Tech license capabilities, all the better!

 

[kayn1n32008]

The issue I've seen with these cheap garbage radios isn't just on harmonics of the fundamental, it's that they generate garbage across the spectrum in addition to harmonics.

 

[N4SRN]

The issue I've seen with these cheap garbage radios isn't just on harmonics of the fundamental, it's that they generate garbage across the spectrum in addition to harmonics.

Yes, one can see that in a signal analyzer, but does this significantly interfere with radio communication using other "quality" radios?

I put a Diamond SRH7CA antenna on my TinySA and 30dB attentators on my UV-5R antenna, and saw no rise in the noise floor across 0-500 MHz nor any signals that popped up in the 144-148 MHz 2m band when I TX'd at 146.520 MHz or in the 420-450 MHz 70cm band when I TX'd at 435 MHz. One spurious emission just below the 1.25m band TX'ing on 146.520 MHz, so that could be in-band above that TX frequency.

I think "quality" radios have adequate sensitivity/rejection to address all but spot-on frequency interference from a UV-5R even if out-of-spec.

From a quick Amazon check, over 25k UV-R5s have been sold, so there's probably many more out there. Most owners probably try a few TXs, get no replies, and shelve the units, like most Tech Hams with their HTs.

 

[kayn1n32008]

Yes, one can see that in a signal analyzer, but does this significantly interfere with radio communication using other "quality" radios?

I put a Diamond SRH7CA antenna on my TinySA and 30dB attentators on my UV-5R antenna, and saw no rise in the noise floor across 0-500 MHz nor any signals that popped up in the 144-148 MHz 2m band when I TX'd at 146.520 MHz or in the 420-450 MHz 70cm band when I TX'd at 435 MHz. One spurious emission just below the 1.25m band TX'ing on 146.520 MHz, so that could be in-band above that TX frequency.

I think "quality" radios have adequate sensitivity/rejection to address all but spot-on frequency interference from a UV-5R even if out-of-spec.

From a quick Amazon check, over 25k UV-R5s have been sold, so there's probably many more out there. Most owners probably try a few TXs, get no replies, and shelve the units, like most Tech Hams with their HTs.

The problem isn't at the fundamental frequency, and users on the fundamental frequency, it's other users of the spectrum, that the spurs are radiating at. Some of the garbage Chinese radios radiate on unintended frequencies with more than enough power to be causing problems.

 

[AK9R]

Yes, one can see that in a signal analyzer, but does this significantly interfere with radio communication using other "quality" radios?

The people who wrote the rules for amateur radio apparently thought that spurious emissions were a potential problem for the entire radio spectrum, not just for other radios operating in the same radio service.

Whether a "dirty" Baofeng interferes with other radios is not the issue. The issue is that amateur radio operators are given tremendous freedom to experiment with various communications modes, to operate high-power transmitters, and build their own transmitters. In exchange for this freedom, amateur radio operators are given a set of technical standards that they are expected to meet. Among them are "don't transmit with radios that produce spurious emissions".

Contrast this with GMRS where licensees are required to buy commercially-produced FCC-certified transmitters, are limited to 50 watts, and can only use analog FM (with limited exceptions).

We might question why amateur radio has these technical standards, but I, personally, don't spend a lot of time thinking about whether or not violating these standards might cause a problem...the rules are still the rules. In other words, we might be able to justify bending the rules for technical reasons, but, administratively, we still have to follow the rules.

For amateur radio transmitters operating between 30 and 225 MHz, the spurious emissions must be at least 60 dB below the fundamental. If that transmitter has a mean power of 25 watts or less, the spurious emissions must not exceed 25 µW (yes, that's microwatts) and must be at least 40 dB below the fundamental.

I can't tell you which radio I was testing in the attached screen capture, but the trace is typical of cheap, Chinese radios from 5-6 years ago. Note that the second and third harmonics are 46 dB down from the fundamental. That's great! But, the second and third harmonics are still greater than -16 dBm (25 µW), so they exceed the limits imposed by the rules. (Before someone asks, a 40 dB attenuator was used on the spectrum analyzer input.)

 

[AB5ID]

For amateur radio transmitters operating between 30 and 225 MHz, the spurious emissions must be at least 60 dB below the fundamental. If that transmitter has a mean power of 25 watts or less, the spurious emissions must not exceed 25 µW (yes, that's microwatts) and must be at least 40 dB below the fundamental.

Thanks for the great explanation. Just to check if I am understanding correctly. For a typical 5 watt handheld, any spurs need to be -53 dBc or better?

 

[AK9R]

For a typical 5 watt handheld, any spurs need to be -53 dBc or better?

At least 40 dB below the fundamental (-40 dBc) and less than 25 µW.

 

[kayn1n32008]

The people who wrote the rules for amateur radio apparently thought that spurious emissions were a potential problem for the entire radio spectrum, not just for other radios operating in the same radio service.

Whether a "dirty" Baofeng interferes with other radios is not the issue. The issue is that amateur radio operators are given tremendous freedom to experiment with various communications modes, to operate high-power transmitters, and build their own transmitters. In exchange for this freedom, amateur radio operators are given a set of technical standards that they are expected to meet. Among them are "don't transmit with radios that produce spurious emissions".

Contrast this with GMRS where licensees are required to buy commercially-produced FCC-certified transmitters, are limited to 50 watts, and can only use analog FM (with limited exceptions).

We might question why amateur radio has these technical standards, but I, personally, don't spend a lot of time thinking about whether or not violating these standards might cause a problem...the rules are still the rules. In other words, we might be able to justify bending the rules for technical reasons, but, administratively, we still have to follow the rules.

For amateur radio transmitters operating between 30 and 225 MHz, the spurious emissions must be at least 60 dB below the fundamental. If that transmitter has a mean power of 25 watts or less, the spurious emissions must not exceed 25 µW (yes, that's microwatts) and must be at least 40 dB below the fundamental.

I can't tell you which radio I was testing in the attached screen capture, but the trace is typical of cheap, Chinese radios from 5-6 years ago. Note that the second and third harmonics are 46 dB down from the fundamental. That's great! But, the second and third harmonics are still greater than -16 dBm (25 µW), so they exceed the limits imposed by the rules. (Before someone asks, a 40 dB attenuator was used on the spectrum analyzer input.)

View attachment 169311

Sadly, I've had many a conversation on here, and elsewhere, where hams simple don't give a flying **** about those rules and requirements for harmonic/spurious suppression, because it's a $20 POS that 'works great'. There is a reason there should be a price barrier to entry to this hobby

 

[prcguy]

The people who wrote the rules for amateur radio apparently thought that spurious emissions were a potential problem for the entire radio spectrum, not just for other radios operating in the same radio service.

Whether a "dirty" Baofeng interferes with other radios is not the issue. The issue is that amateur radio operators are given tremendous freedom to experiment with various communications modes, to operate high-power transmitters, and build their own transmitters. In exchange for this freedom, amateur radio operators are given a set of technical standards that they are expected to meet. Among them are "don't transmit with radios that produce spurious emissions".

Contrast this with GMRS where licensees are required to buy commercially-produced FCC-certified transmitters, are limited to 50 watts, and can only use analog FM (with limited exceptions).

We might question why amateur radio has these technical standards, but I, personally, don't spend a lot of time thinking about whether or not violating these standards might cause a problem...the rules are still the rules. In other words, we might be able to justify bending the rules for technical reasons, but, administratively, we still have to follow the rules.

For amateur radio transmitters operating between 30 and 225 MHz, the spurious emissions must be at least 60 dB below the fundamental. If that transmitter has a mean power of 25 watts or less, the spurious emissions must not exceed 25 µW (yes, that's microwatts) and must be at least 40 dB below the fundamental.

I can't tell you which radio I was testing in the attached screen capture, but the trace is typical of cheap, Chinese radios from 5-6 years ago. Note that the second and third harmonics are 46 dB down from the fundamental. That's great! But, the second and third harmonics are still greater than -16 dBm (25 µW), so they exceed the limits imposed by the rules. (Before someone asks, a 40 dB attenuator was used on the spectrum analyzer input.)

View attachment 169311

25uW is -16dBm so it appears the radio under test is out of spec by 6.62dB even though the 2nd harmonic is -46.61dBc.