|[AMRadio] RE: Bandwidth Proposal|
k4kyv at hotmail.com
Mon Aug 16 00:25:20 EDT 2004
One problem I see is that the FCC has a habit of twisting rulemaking
requests to fit its own agenda as the actual rules are formulated, and
sometimes the end result has little resemblence to the original proposal.
Those who were around in the mid 70's will recall a similar plan was
proposed once before, under the infamous Docket 20777. Under that proposal,
AM would have been outlawed on 160-15m by imposing a maximum 3.5 kHz
bandwidth limit on all amateur frequencies below 28.5 mHz. Yet according to
the FCC, the purpose of that proposal was DEREGULATION!!! AM would have
been deregulated out of existence. Thanks largely to a strong response by
the AM community, the proposal was eventually scrapped.
In this petition ARRL requests that the FCC once again consider defining
subbands by bandwidth instead of emission mode, with an exceptional 9 kHz
limit for DSB AM. Nevertheless, it would be very easy for the Commission to
write a rule similar to what ARRL has proposed, but omit the DSB AM
exception. Or to place an expiration date on it, as they did with the 1 kw
power limit grandfather clause.
Remember, the AM power fiasco was the result of an original idea that
sounded simple enough: measure amateur power as rf output instead of dc
input. The actual changes in legal power were "collateral damage" that went
far beyond the alleged intent of the rulemaking proceeding. Incredible as it
sounds, the FCC's rationale for reducing AM power was that the FCC thought
its field inspectors were somehow unable to measure the power levels of SSB
If and when the petition is given an RM- number, it is imperative that the
the heaviest response come from the AM community.
Even if adopted as proposed, it would impose NEW RESTRICTIONS on AM
operation. To-day, we have no specific legal bandwidth limits, other than
the clause that operation be kept within the bounds of good engineering and
amateur practice. If, for example, a group of locals wanted to experiment
with super hi-fi AM (or SSB for that matter) on 160m during the daytime when
the band is essentially dead, there would be no legal problem with
transmitting a 30-kHz bandwidth or wider signal as long as no-one else was
being interfered with. Once a legal definition is in the rule book, it is up
to whoever is in charge of FCC policy at the time to determine how the rule
will be enforced.
9 kHz would be about the minimum practical bandwith for AM if a legal limit
is adopted. That would allow each sideband to be 4.5 kHz wide, meaning that
the highest audio frequency would be 4500~. It is very difficult to build a
high pass filter with extremely sharp cutoff at, say 3000 Hz. Filters tend
to have a more gradual cutoff, plus no transmitter is distortion-free. In
order to accomode a full frequency response up to to 3000 or 3500~, a total
legal bandwidth of at least 9 kHz would be necessary in the case of
practical amateur radio transmitters.
Although this has not been a major issue in recent years, if the no-code
proposal eventually passes and results in an influx of newcomers, I'm afraid
there will be renewed bandwidth pressure on the AM mode. That is one of the
reasons I have remained opposed to eliminating the code test for the HF
>From what I have read on the website so far, it looks like the ARRL proposal
would result in a very complex subband structure, involving combinations of
mode bandwidths and licence class.
It would be a lot simpler to do away with government imposed subbands
altogether as they recently did in Canada, and let amateurs work out our own
band plans as we have already done on 160m.
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