|[AMRadio] AMRadio Digest, Vol 119, Issue 55|
k4kyv at charter.net
Mon Dec 16 17:12:53 EST 2013
>>On Monday, December 16, 2013 1:04 PM, W. Harris <nbcblue at hotmail.com>
I keep hearing people talk about broadcast quality in regards to ham radio
AM transmissions. Why should anyone strive for such quality when the object
is to communicate using no more band width than necessary?
Bill - K5MIL
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That sounds like SSB propaganda from the 1950s.
If the only purpose of amateur radio is to communicate, using no more
bandwidth than necessary, then why even run phone at all? CW and PSK run a
LOT less bandwidth than AM or SSB, and we can still communicate 100% using
those super-narrow modes.
Good operating practice suggests having the capability of adjusting one's
transmitted bandwidth according to conditions, just as we have variable
selectivity on our receivers. There is nothing wrong with transmitting full
bandwidth broadcast quality AM provided the band is not congested and there
is plenty of space to go around. Under congested band conditions,
considerate operators will limit their bandwidth to avoid mutual
interference with adjacent channel QSOs.
And, remember, we hear two different kinds of "wide" signals. Most of the
splatter and buck-shotting that causes harmful interference results from
spurious sideband products, and this can occur equally with a transmitter
running space shuttle quality audio as with broadcast quality. Sideband
products from a clean signal running audio with full frequency range are
less obnoxious and less destructive than spurious sideband products
resulting from audio distortion, flat-topping and overmodulation. It is easy
enough to limit upper frequency response under congested band conditions,
and the appropriate upper mid-range boost can make up for the lack of
extreme highs when the frequency response is limited.
In my own station, for years I have had the option of a sharp cut-off,
brick-wall, low pass audio filter combined with suitable "presence rise",
and I often receive reports of "broadcast quality" even when using the
filter to cut off everything above 3400 cps. Under less crowded band
conditions, I normally switch to a more gradual cut-off low pass filter
that begins to roll off around 5,000 cps. I see little point in transmitting
audio out to 10 kc/s or more, since few if any receivers would have their
selectivity set wide enough to receive it.
Although a couple of AM operators who frequent 75m seem to take pride in the
broadness of their signals and have generated more than a little ill feeling
against AM, I am still utterly amazed when the band is sparsely populated
and there may be wide swathes of unused frequencies to both sides of an
existing AM QSO, and someone will start up less than 5 kc/s away from the
carrier frequency and then proceed to complain about the interference.
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