As to banning certain radios…

(Note I would post this on the N4NJJ site, but he’s got it locked down on a subscription basis.)

N4NJJ says (regarding inexpensive Chinese radios), “…these radios are not capable of pre-emphasis or de-emphasis…”, then N4JJ goes on to say that he’s been a ham for over a decade and until recently he didn’t know about emphasis. Finally, he goes on to declare that the claimed lack of emphasis in the Chinese radios is in large-part the reason why he is going to ban all users of these radios from his repeater.

Well, here’s what I have to say about that…

Without proper testing and presentation of the evidence, I think N4JJ is wrong to publicly claim a particular brand of radio does not employ industry standard emphasis, then use that unsubstantiated claim as basis in large-part to ban a whole class of operators using said radios from his repeater system.

I don’t own any of these cheap Chinese radios, nor do I have a schematic (yeah, as if you could trust the schematic).

But I do know this…

1. Emphasis (pre-emphasis in the Tx and de-emphasis in the Rx) is not a simple thing to test, especially in the receiver. You have to break the Tx-Rx link and look at the transmitter and receiver separately. You will need a spectral plot of the audio chain, ideally in real time. You will also need clean, stable audio and RF frequency-variable sources with some means of level adjustment and impedance matching.

When testing the receiver it is very important to inject a clean in-band carrier that brings the radio out of open-squelch and into the operating region, but far from full-quieting. Keep in-mind the AGC loop is working against you during this process. It is only at this operating point that you can properly observe the de-emphasis response in operation, and take data.

2. Since we’re talking about analog NBFM radios here, the pre-emphasis and de-emphasis would likely follow (at a minimum) the TIA/EIA-603 standard. This would require including a simple RC high-pass then RC low-pass filter. The total additional cost to the radio is negligible, as is the cost of designing the filter in. To not include even the simplest implementation of emphasis in the Chinese radios is quite unlikely, especially because of the problems it would cause with reduced link performance and distorted audio when used with industry-standard equipment. Note: In-practice, emphasis does employ a slightly more complex filter than the bare minimum required, this is to help suppress sub-audible tones. But again, the realization employs only passive RC components and is very simple and cheap to include.

3. Assuming you have a reliable and up to date schematic for the radio, simply looking at the circuit often will not reveal precisely where the emphasis takes place. In other words, if you’re looking for a simple RC filter, and don’t find it sticking out like a sore thumb where it should be on the schematic, don’t assume there is no emphasis included! Skilled analog engineers are masters at tailoring frequency response without adding components, or adding components where you would least expect. I can’t go into this subject in-depth here but just to give you a taste: If you need to add (e.g.) an nth-order high-pass slope to a stage, before adding new components you would first look to employ existing interstage input/output characteristics such as coupling components, impedance, gain distribution (which changes coupling capacitance through Miller effect), etc. So if you think something is missing and/or out of place on the schematic just by looking at it – don’t.

4. Today, it is possible that emphasis is built-in to the radio’s integrated circuit. This is especially the case with modern radio-on-chip components which internally implement the radio as a direct conversion quadrature detector and accompanying on-die DSP. These highly integrated solutions are typically more difficult to test than analog designs, and referring to the schematic (assuming it is correct) will not help you to identify how the emphasis is employed.

The anti-Baofeng guy is just being a real tool.

He claims that the Baofeng radios don’t have proper FM emphasis and de-emphasis — they do, it’s in the specs, the normal 6dB/octave pre-emphasis. He cannot explain the what and why FM transceivers have pre-emphasis and de-emphasis. I hear Baofengs all the time on my 2m system, and they sound fine, once the lids^h^h^h^h new hams turn off their roger beeps.

It’s especially silly to be acting all elitist when he’s not even running what “real repeater elitists” would call a “real repeater” — he’s got some antique Motorola junker made out of mobile radio parts (a GR-1225) on a Diamond antenna with some cheap foil-shielded feedline. Maybe this is why some radios sound like crap on his system.

The guy is acting the fool, saying he’s not an elitist while running an unpublished tone and required MDC tones for access to his toy repeater.

Bah.