fcc rule limiting transmitter output for class c AM

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stephend2
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fcc rule limiting transmitter output for class c AM

Post by stephend2 » Mon Jan 27, 2014 12:28 am

I've been told of a rule that limits the licensee of a class c station to using a transmitter capable of no more than 1kw carrier. I'm not finding this rule anywhere, some pointers would be helpful if this still exists. Owner has a lead on a 5kw transmitter for a really good deal but we need to know if it can legally be used on a class c station.

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Re: fcc rule limiting transmitter output for class c AM

Post by w9wi » Mon Jan 27, 2014 7:41 am

I believe you're talking about 73.1665 (http://edocket.access.gpo.gov/cfr_2012/ ... 3.1665.pdf), which prohibits the use of a transmitter rated for more than 1kw at an AM station whose authorized power is 1kw or less.
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stephend2
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Re: fcc rule limiting transmitter output for class c AM

Post by stephend2 » Mon Jan 27, 2014 8:13 am

That's it, thanks. I must have skirted all around that page in my searches.

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Re: fcc rule limiting transmitter output for class c AM

Post by w9wi » Mon Jan 27, 2014 9:44 am

It's not under the AM-specific rules. (even though there is no similar rule for FM or TV and 73.1665 specifically says so..) It's under "rules applicable to all broadcast stations". An awful lot of rules aren't where you might expect to find them.....
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Deep Thought
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Re: fcc rule limiting transmitter output for class c AM

Post by Deep Thought » Mon Jan 27, 2014 11:29 am

As a practical matter, I haven't seen that enforced in decades. In fact, a 650-watt class-B station I was working on this summer was issued a license despite the license application clearly stating that it had installed a 2.5 KW transmitter (there is some upgrade potential here). 5 KW on a 1 KW class-C where such an upgrade is not possible may be a push, though. You can always call and ask...you'd be surprised how helpful the Media Bureau staff is.
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Re: fcc rule limiting transmitter output for class c AM

Post by kcbooboo » Mon Jan 27, 2014 12:18 pm

And it seems that there's no such limitation on the auxiliary transmitter, so who's going to know if your 1kw main went down and all you had available was a 5kw backup, which you're now running on the air at 1kw.

I'm sure there are some efficiency considerations to think about when running a 5kw xmtr at 1kw.

Another one of those outdated rules that should have gone away or been applied equally to all broadcast services. Maybe this one can vanish during the AM Revitalization cleanup.

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Re: fcc rule limiting transmitter output for class c AM

Post by Deep Thought » Mon Jan 27, 2014 2:03 pm

This has nothing to do with "revitalization" and was not part of the docket. And a 5 KW backup for a class-C will raise some eyebrows if you are suspected of running over-power.

This same thing came up awhile ago when Nautel started selling 12 KW transmitters which are routinely installed at 10 KW stations. Technically they are illegal to use for the main, but as I said, I doubt this has ever come into play unless someone was doing something very stupid like running 5 KW on a class-C on the US mainland.
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stephend2
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Re: fcc rule limiting transmitter output for class c AM

Post by stephend2 » Thu Jan 30, 2014 8:23 pm

On solid state, would there be a noticeable efficiency difference between running at 5kw or 1kw ? I'm speaking specifically of a Harris Gates One here.

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Re: fcc rule limiting transmitter output for class c AM

Post by Deep Thought » Thu Jan 30, 2014 9:53 pm

Do you mean a Gates 5 vs a Gates 1?

The overhead on those is pretty similar since they do not have cooling fans and the control electronics is the same on both but the overall efficiency will be lower on a 5 running at 1 KW than a 1 at 1 KW. Here's what Harris has from the brochures:

Power Consumption:
ONE: At 1000 Watts carrier: 1428 Watts typical at 0% modulation, 2143 Watts typical at 100% sinewave modulation, 1607 Watts or less during typical programming.
TWO: At 2500 Watts carrier: 3846 Watts or less at 0% modulation, 5769 Watts or less at 100% sine wave modulation, 4807 Watts or less during typical programming.
FIVE: At 5000 Watts carrier: 7692 Watts or less at 0% modulation, 11,538 Watts or less at 100% sinewave modulation, 9615 Watts or less during typical programming.

This is from the Gates 5 tech manual. Maybe you can extrapolate something useful.
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Re: fcc rule limiting transmitter output for class c AM

Post by Shane » Sun Feb 02, 2014 4:29 pm

<silly comment mode on>

Would this rule be moot since it states the chart applies to a main transmitter that isn't working? (It says, "...stalled at an AM station...")

<silly comment mode off>
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