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Modern radios

Discussion in 'Amplitude Modulation' started by N2DTS, Nov 21, 2019.

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  1. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Yep, ham radio audio is supposed to sound tinny, scratchy and distorted...

    ...just like the audio we hear from space shuttle voice comms, and the EAS alert warnings that destroy TV programs every time a little thunderstorm passes over. How nice!

    Ham radio is a hobby! It's for whatever purpose we want to make of it.
    W9FMC, K4EI and AG5CK like this.
  2. K5MIL

    K5MIL Ham Member QRZ Page

    No, not for whatever we want to make of it. You think it would be OK to transmit music on the ham bands?
    § 97.307 Emission standards.
    (a) No amateur station transmission shall occupy more bandwidth than necessary for the information rate and emission type being transmitted, in accordance with good amateur practice.

    (2) No non-phone emission shall exceed the bandwidth of a communications quality phone emission of the same modulation type. The total bandwidth of an independent sideband emission (having B as the first symbol), or a multiplexed image and phone emission, shall not exceed that of a communications quality A3E emission.

    Bill - K5MIL
    WA5VGO likes this.
  3. K4KYV

    K4KYV Premium Subscriber Volunteer Moderator QRZ Page

    Music has nothing to do with it. The rules expressly prohibit music. Nothing in the rules say that the purpose of amateur radio is specifically 'communication'. AR is not a personal communications service like CB and Land Mobile. AR is a technically oriented radio service, and its Bases and Purposes include experimentation and self-instruction in the radio art. Sound quality of voice transmission would fall into those categories.
    That leaves a lot of leeway, and doesn't specifically restrict amateur communication to space-shuttle audio. Aren't the articulation components of the human voice part of the 'information rate' being transmitted? The emission type AM is defined in Part 97 as A3E, not 6A3E. The FCC has deliberately omitted any specific numerical limits to transmitted bandwidth, allowing amateurs the maximum flexibility for experimentation, communication and self-instruction in the radio art. Riley Hollingsworth once re-stated that when he answered a question at an FCC Forum at the Dayton Hamvention a few years ago. Good amateur practice would suggest reasonably limiting transmitted bandwidth during congested band conditions, but when the band is lightly occupied as is often the case to-day, there is no reason not to transmit wider-band higher fidelity phone. Just as we use a narrower selectivity on our receivers on a congested band, but open up to wider selectivity when activity is light.

    So what does that have to do with AM? Isn't AM a phone emission? Furthermore, AM and independent sideband emissions are two different things.

    There is no justification to continue the tired old obsession with 'bandwidth' and 'spectrum conservation' of the past. The HF bands and 160m are no longer congested to the hilt with signals as they were a few years ago when during peak hours one had to search for a clear spot to transmit. Now, there are usually multiple swathes of unoccupied frequencies between QSOs, even on a QRN-free weekend. Despite the highly touted record number of licensees in the FCC data base, more than 700,000, activity in the HF and 160m bands has decidedly dwindled in recent years, while some of the phone bands have been expanded. The bands simply aren't as crowded as they were back in the 60s and 70s.

    The 'bandwidth' bus left the station several years ago.
    W9FMC, K4EI and WZ5Q like this.
  4. AG5CK

    AG5CK Premium Subscriber QRZ Page

    I agree, but it's a two way street.
  5. KB8VUL

    KB8VUL Ham Member QRZ Page

    So I got ask about repairs I do, on SMD equipment.
    So, since you may not be aware. I am a two way commercial tech.
    I repair radios weekly. Using hot air soldering equipment and preheat units to remove and replace any sort of parts including VLIC (very large integrated circuit) clips
    I don't do any BGA stuff as we don't have the machines to reball chips, which is a totally different thing.
    So yes, I do work on SMD boards. With the right gear it's not really complex. But as I said before. You can't do it with an iron that you would have used on a 1950's Collins.
    Mind you, most of the stuff I work on has a big M cast in the top of it and cost 3 to 5 grand. Would I put that level of effort into a Baofeng. Of course not.
    But to claim that this gear is simply not repairable is silly. A basic cheap hot air / iron rework station, with the same quality as a Baofeng, is $100-$200 on eBay. Another $150 will
    get you an infrared preheat unit and you can do 90% of all repairs on ANYTHING that is PC board based. Because, the irons at least are fairly low wattage and will NOT unsolder wires wrapped through terminal boards
    under the bottom panel in a 1950's Collins 32V. Yes, I have worked on those too. I have worked on countless radios. Two-way, ham, commercial broadcast. It's all the same stuff. A VCO / crystal / LC oscillator feeds out into an IF section and mixed with an IF frequency creating the desired RF frequency. The signal is then sent through amplification stages until it is of the desired level. Somewhere along the way audio that has come from a microphone and been amplified is run into either a modulation transformer (old school) or swings a DC voltage on a transistor controlling the amplitude of the RF signal. It's then shipped out a connector of some sort to an antenna. AM radio transmission. Full analog. The digital version is a bit more complex, and I will not bore you with it. FM of course, the audio goes into the VCO via a variactor diode which changes the frequency slightly as opposed to changing the amplitude. But it IS all the same.

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