[AMRadio] RE: Bandwidth Proposal


Donald Chester 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 
transmitters!

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 
licence.

>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.

Don K4KYV

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