5KC Audio

[WD8BIL]

Brian said:

For all practical purposes narrow band AM on the amateur radio bands (including the CB band) is suppose to be 5kcs.

Says who?? Part 97 doesn't specify!

[ka3zlr]

-Raises head above the crowd-

Are we Blocked.. [] Can we Talk Audio here..LOL...
Peeking from the Peanut Gallery.

[KF1Z]

Since it all got deleted... for whatever reason...

That was my point in the first place....

The post  seemed to say that some, (really quite a few ) are breaking "the rules" by exceeding 5khz bandwidth.

No bandwidth specifications are given in the FCC rules AS THEY  PERTAIN TO AMATEUR RADIO operation.

Someone's perception of what "good operating pratice" is, is just that... a perception.. a thought... a concieveable meaning...  not a rule.

If proven otherwise, then I will install filtering etc where needed....
Since my class-e rig's filters START to roll off the audio at 7.5khz...

[ka3zlr]

I had to modify this:

I couldn't have "Never" said it any better or as Eloquent Excellent...and Thank You

[WD8BIL]

Exactly.
Having a setup that does good audio out to 10Kc is like having a stereo with 200 watts per channel. Chances are you'll never use it but it insures good operation where you normally do. HEADROOM BABY!

[k4kyv]

Even the FCC hasn't gone along with a maximum of 2.5 kc/s of audio (5 kc/s total occupied bandwidth) in the past.  Under the infamous Docket 20777, the original regulation-by-bandwidth proposal, the proposed bandwidth limit was 3.5 kc/s. And that was to accommodate slopbucket, since AM would have been precluded if that proposal had passed.

Another time when they proposed to sneak in a specific bandwidth limitation, through the "plain language" proposal of the 1980's that would have rewritten the amateur rules into the same Q-A format as they have for the CB rules, the maximum proposed occupied bandwidth (that specifically accommodated AM that time), was 7 kc/s.

[KF1Z]

Yes,

Sort of  like having an RF deck or amp, CAPABLE of 1kw+ RF outpoot... peaks to 6kw...

It's just nice to have the headroom...  

Not that anyone here would ever use such a thing to it's full capabilities on the air .....  

[ka3zlr]

Headroom is the answer to this... in case of a Sneeze cough Laughter at a high note my voice has changed alot since the cancer I have a real High Pitched Laugh now That i never had my voice has changed considerably.

[David, K3TUE]

I have seen mention of transmitted bandwidth for amateur audio and other modes in the documents of other countries, in ITU, and in WARC information.  But I have never noted them in US documents pertaining to amateur radio.  Or have I missed them?

[ka3zlr]

You Don't have to leave Brian, everyone in here enjoys
nothing More than Discussing Audio stick around man Dig in  

This is where everyone in here Shines  

73

Jack.

[k4kyv]

Exactly.
Having a setup that does good audio out to 10Kc is like having a stereo with 200 watts per channel. Chances are you'll never use it but it insures good operation where you normally do. HEADROOM BABY!

To be more precise, it's not a matter of headroom, but of linear phase response within the desired bandwidth of the audio that is actually transmitted.  The UTC transformer company recommended in their old LS-series catalogue that audio iron have a flat frequency response at least one octave above and below the actual intended frequency range of the amplifier.

That means, if you wanted to transmit "communications quality" audio 300-3000~, you would need a flat response capability of at least 150-6000~. The nominal 50~ to 10,000~ response of a lot of the old broadcast iron was really optimum for more like 100~ to 5,000~ audio to modulate the carrier, which would be more typical of what AM broadcast stations throughout the 30's and 40's actually transmitted.

If the response of the amplifier is too restricted, the  result will be phase shift distortion, which can be a particularly bad problem on the low end due to waveform tilting.

Of course, AM broadcast audio has always been somewhat of a moot point, since the vast majority of receivers, then and now, aren't much better than telephone quality, particularly on the high end.  Many of the old sets that touted "hi-fi" audio, with good audio iron and speaker(s), and a push-pull final audio stage, severely restricted the high end due to a poor i.f. selectivity curve.

[W2ZE]

But I have never noted them in US documents pertaining to amateur radio.  Or have I missed them?

There are rules regarding occupied and necessary bandwidth in 47CFR 2.202. The reason most people don't see them is because they are not defined in Part 97, but in part 2. Parts 0,1, and 2 are general rules and regulations that pertain to all commision licensees. Hope this helps.

Mike,W2ZE

[k4kyv]

There are rules regarding occupied and necessary bandwidth in 47CFR 2.202. The reason most people don't see them is because they are not defined in Part 97, but in part 2. Parts 0,1, and 2 are general rules and regulations that pertain to all commision licensees. Hope this helps.

For the full text (subpart C), go to:

http://edocket.access.gpo.gov/cfr_2002/octqtr/pdf/47cfr2.201.pdf

and

http://edocket.access.gpo.gov/cfr_2002/octqtr/pdf/47cfr2.202.pdf

Those rules appear to define the meanings of necessary and occupied bandwidth and various modes of emission, but don't give any specific limitations that would apply to a specific service, such as broadcasting and amateur.  I would think everyone would agree that there are differences in the bandwidth standards expected with those two services, but that is not to say that amateur radio voice transmissions necessarily have to be limited to "communications quality" or telephone quality audio.

[ka3zlr]

Hey Don I was reading this:

http://edocket.access.gpo.gov/cfr_2008/octqtr/pdf/47cfr2.202.pdf

an there's a statement about 0.5 percent of the total mean power..??

sup with that..

Jack.

[k4kyv]

As I interpret it, it means that the occupied bandwidth is defined as the bandwidth in which 99% of the total power emitted by the transmitter lies.  The remaining 1% of total mean power lies outside that bandwidth, with half (0.5%) lying above and half below the specified range.

[ka3zlr]

Cool Thanks Alot.

Jack.

[W1VD]

Just ask yourself this guys, why is the typical AM receiver bandwidth 6kc?

Holdover from the old days when transmitter and receiver 'dispatch' audio was in vogue? Modern receivers have bandwidths that are selected independent of mode.   
   

[ka3zlr]

Why there's such an effort in the Receiving Dept. the melding of the old with the new

The warmth and Fidelity of yesterday with today's components to bring it through .

The very best that can be had is now a possibility with a minimum of effort

Man it don't get any better than that.

Till we see what the future brings.

[KM1H]

Just ask yourself this guys, why is the typical AM receiver bandwidth 6kc?

I dont know of any "typical" set that did that except Collins A3/A4 who liked the space shuttle audio sound in their transmitters also.

Most were 8-10kc and even the high end SS HRO-500 had a 8kc position as did the true classic AM radio, the NC-300.

The ceramic filters many of us insert in 455kc IF's are 8-9kc and the cheap 4 pole Heath SB xtal version was 5kc on the nose but a nice 15kc at 50dB down giving a real nice sound on strong signals.

I particularly like the IF transformer only sound of the HRO-60 and NC-183D while some prefer the wider sound of the HRO-50, NC-183, SX-28/32, etc. or the in betweeen HRO-50-1, and early HQ's with the 3 stages of 455kc IF. The pre SP-600 Hammarlund Super Pros with the variable IF BW are nice also as the wider coupling for increased selectivity also pulls in the skirts. Not bad for only 3 stages of IF. And I know JN agrees about the performance of the NBS-1 when the going gets tough. Another surfaced at the Utica hamfest and followed a local friend home.

Carl

[Todd, KA1KAQ]

Just ask yourself this guys, why is the typical AM receiver bandwidth 6kc?

The pre SP-600 Hammarlund Super Pros with the variable IF BW are nice also as the wider coupling for increased selectivity also pulls in the skirts. Not bad for only 3 stages of IF.

Out to 16 kc, in fact. 465 IF frequency though, that's gotta be why they're so great sounding.  

Just a quick scan of a few receivers here(SP-10, 100, 200, NC-2-40D, SX-28A, etc etc) shows virtually all have rather broad capability. In fact, the restricted communications-quality audio only came into vogue in the 50s, mainly around the time of the arrival of SSB. Collins was all about comms, punching through and hearing under bad conditions which their gear did quite well at. Though you can easily plug a 8 or 9 kc mechanical filter into the 75A-4 and away you go. Some have even retrofit R-390A filters before the Curry filters were an option.

Along with the A-4, later rigs like the Mohawk, SX-115 and others clearly had primarily SSB in mind, not AM. Following on the restricted receiver approach came transceivers that dropped AM all together, starting with the Collins KWM and S-Line rigs. Basically they were building to what they felt the market wanted or would want. Eventually other manufacturers followed suit, and for years it was tough to buy a new transceiver that included AM.

Then a funny thing happened. The AM mode reappeared. I suspect it has zero to do with following some 'typical bandwidth' scheme and more to do with plain old marketing and demand. Business band requirements are totally different than those required for the amateur service, broadcast, etc.

But I'm preaching to the choir here. You've got pretty much all of the HiFi receivers in your stables, Carl, so you clearly understand the differences. 

[Pete, WA2CWA]

Along with the A-4, later rigs like the Mohawk, SX-115 and others clearly had primarily SSB in mind, not AM. Following on the restricted receiver approach came transceivers that dropped AM all together, starting with the Collins KWM and S-Line rigs. Basically they were building to what they felt the market wanted or would want. Eventually other manufacturers followed suit, and for years it was tough to buy a new transceiver that included AM.

Then a funny thing happened. The AM mode reappeared. I suspect it has zero to do with following some 'typical bandwidth' scheme and more to do with plain old marketing and demand. Business band requirements are totally different than those required for the amateur service, broadcast, etc.

True for most of the American manufacturers, and a few foreign ones, from the time Collins started the trend but Yaesu, never gave up the AM mode, nor did most of the Icoms. Kenwood  only dropped AM from their hybrids, TS-520, 530, 820, and 830 although the 830M (with AM capability) was sold in foreign markets and the TS-120, 130, and 180 solid-state rigs also lacked an AM mode.

[ka3zlr]

There's a "Yea Butts" there though...sure there was what they decreed as AM on their rice machines but ya might as well be channelized it's just wasn't good enough trying Appease the masses one would think, but Experimentation has led down a Better Trail and that is what this is about Experimentation where we have a license to do so this is a Good thread keep it going.

73

Peanut  

[k4kyv]

The early A4s had decent high frequency response, but restricted the low end with 0.01 mfd coupling caps.  Later on, they added a couple of 510 pf caps between plate and ground of a couple of the audio stages to further reduce the highs.  I think one of the reasons they restricted the lows is that the receiver has a hum problem, and limiting the low end makes it go away.  IMO, the problem is due to the fact that they use the chassis for the ground return for the tube filaments. They should have wired both sides of the filaments with real hookup wire back to the transformer, and grounded the midtap to chassis.  I had thought of rewiring mine, but gave up on the idea after looking at the  rats nest of wiring I would have to work through to make the mod.  It would be much easier to add a rectifier and filter and run all the filaments on  DC.

I removed the 510 pf caps, which improved the highs, and did what I could to get rid of the hum,  then bridged 0.1 mfd caps across the stock 0.01 mfd coupling caps (way too much trouble to remove and replace them without burning up other components and melting wire insulation with the soldering iron). That helped tremendously to get decent AM audio out of the A4.  But later, when I acquired the Sherwood sync detector, I run the audio through that to my outboard audio amp, and by-pass  the stock A4 audio altogether.  Just no comparison between the stock audio and what I have now, even considering the rough edge that the mechanical  filters add to the audio.

[ka3zlr]

Ok My turn Before I got all Involved with my Newer Spectrum Analyzer an my computer Spectrum analyzer and Processing Software etc etc...One analyzer has quit on me Bummer it was present from a former RCA employee  

Long story short I always Like My SX28 it ain't the best it ain't the worst it's Pre war it's older than Dirt but it looks the bestest when it's Lit up

That's my story an I'm keepen to it.



73 KA3ZLR.

[WD8BIL]

A lot of commercial two-way stuff it like that, they want 2.5kc max on each side just like NBFM. Normally its better to see it at 2.7kcs on each side and you still have enough headroom for the typical 6kc receiver passband filters. Goerge’s write-ups said 2.8kc on each side, but its right on the hairy edge and 3.0kcs would be the max. Some 6kc receiver filters may handle it and some won’t, it just depends.

We were talking about Amateur AM, Brian. Now your on commercial NBFM stuff.
In the context of the commercial stuff I'd hafta agree with ya. 5KC does hang out there a lot.

But your question :

Just ask yourself this guys, why is the typical AM receiver bandwidth 6kc?

Implied amateur AM receivers. With the list of THOSE receivers posted herein it seems 5KC isn't/wasn't "most" of the receivers. Heck, my all American 5 Packard Bell is 8 KC at least.