[BC] Scope for Mod Monitor...

[Mike McCarthy]

I will echo Robert's comment and add that a sweep magnified scope is an 
absolute necessity to properly see negative cut off as well as + peaks.  I 
set a TX one day by this method and the monitor's + peak's were low by 10% 
and "-" peaks low by a couple %.  With a standard scope, there looks to be 
cutoff when there is not.

MM

t 01:10 PM 7/19/2006 -0400, Robert Meuser wrote

>The FCC measure ALL modulation with a scope. This includes FM. Jeff W and 
>Willie have both offered valid ways to set positive mod using a scope 
>although negative peaks are all that really matters..
>
>R
>
>Burt I. Weiner wrote:
>
>>R,
>>
>>Yes, for negative peaks it's very easy to see carrier cutoff.  If you 
>>want to set your modulation for +120% or the maximum 125% positive peaks, 
>>a scope won't cut it.  Tone maybe yes, program, no.  The FCC looks for 
>>excessive (AM) negative peaks with a scope.
>>
>>Burt
>>
>>At 09:38 AM 7/19/2006, you wrote:
>>
>>>From: Robert Meuser <Robertm at broadcast.net>
>>>Subject: Re: [BC] Modulation Monitors...
>>>To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
>>>Message-ID: <44BDE0FD.1090303 at broadcast.net>
>>>Content-Type: text/plain; charset=ISO-8859-1; format=flowed
>>>
>>>Must disagree, Burt.
>>>
>>>The FCC uses a scope for both AM and FM modulation measurements. The
>>>original discussion was limited to AM operation where a scope is the
>>>best way to check modulation. I agree that positive modulation  is a
>>>little more difficult to observe but then I know of no station that
>>>observes the positive modulation rule.  Harold stated a while back on
>>>one of the lists that from his records no station has ever been cited
>>>for positive over mod.  I know of major stations in the top groups that
>>>will not accept equipment that does not do at least 145% positive mod. I
>>>have never accepted at TX that does less than 165% positive mod and have
>>>never run a TX at anything less than 150%. My antenna systems are
>>>contractually speced for 200% mod with continuous tone bursts.
>>>
>>>R
>>>
>>>
>>>Burt I. Weiner wrote:
>>>
>>> > Any station that does not have a properly working modulation monitor
>>> > for their transmitter/s is fooling themselves and whoever is
>>> > responsible should have their head examined.  If you think the
>>> > bargraphs on the front of the transmitter are going to tell you what's
>>> > happening, you're wrong.  A scope is fine to a point but it won't tell
>>> > you if you're modulating 115, 120 or 125 percent positive peaks under
>>> > dynamic program conditions.  You cannot resolve modulation close
>>> > enough with a scope under program conditions.
>>> >
>>> > Burt
>>
>>
>>Burt I. Weiner Associates
>>Broadcast Technical Services
>>Glendale, California  U.S.A.
>>biwa at earthlink.net
>>K6OQK
>>
>>_______________________________________________
>>
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>
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>
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