[BC] Mod Monitors...

[Burt I. Weiner]

   I think I may not have made my point very well.
   Yes,  it's  true  that  you  are  not  required  to  have a modulation
   monitor.   The  rule requiring that you have one was dropped some time
   ago but you are still  continuously responsible for compliance.
   Many  times I've used a scope to set up a station's modulation when no
   monitor  was  available  and  there  was  a  question about modulation
   levels.   Any  decent  oscilloscope will certainly tell you if you are
   cutting carrier.  The problem comes when you try and set your positive
   peaks  to the legal maximum of  125%.  If you have a scope with a peak
   reading  digital  display indication then you can probably come pretty
   close  depending  on  how  well  you  calibrate  for  a zero modulated
   carrier.
   What  I have done when it has been necessary to look at positive peaks
   with  a  scope  is  to  calibrate  +/- two major divisions for carrier
   without  any  modulation,  turn  the horizontal sweep off and move the
   remaining  vertical  trace  just next to the center vertical reference
   graticule on the screen.  Momentarily kill the input and make sure the
   spot  is right on the center horizontal reference line,  This gives me
   the  best  way  to  visually look at peak positive modulation using an
   oscilloscope.    Each  minor  mark  above  carrier  reference  is  20%
   modulation.   One  major division above carrier is 100% modulation and
   one minor division above that would be 120%.  The problem is, how well
   did you calibrate and how well can you resolve the trace.  How good is
   the  focus  and  astigmatism  of  the spot.  You may think this is nit
   picking  but  my  comments  personally come from desiring accuracy.  I
   highly   recommend  to  my  clients  that  they  maintain  a  properly
   calibrated modulation monitor.  It's good, responsible engineering.
   The  issue  may very well come home to roost if there is ever an issue
   with the FCC over your modulation levels.
   Burt
   At 11:30 AM 7/19/2006, you wrote:

     From: "Bailey, Scott&quo     Subject: RE: [BC] Speedometers on Cars.  Do we need them?...
     To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
     Message-ID:

     <50E0246CCF92B64BA1BA4EB56C09CBF005039C1C at bluepost.nes.nespower.nes
     > Content-Type: text/plain;        charset="us-ascii"
     Dennis,
         There  is  nothing  against  having  a  mod  monitor,  but  the
     commission
     doesn't  require it and a good scope I think is the best. I know of
     one
     station  that  the  commission  came  to inspect in this area.  The
     station
     has  no  mod monitor at the studio, nor transmitter site.  It was a
     500
     watt  AM.   They walked in the transmitter site, took a look at the
     bar
     graph  on  the  BE  transmitter, looked at the meter readings, then
     left. No
     question came up about a mod monitor.
     Scott
     When  I  bought my stations 11 years ago, neither the AM nor the FM
     had
     mod
     monitors.  Several  good  engineers and an FCC Field Inspector have
     been
     through  my  plant.  Nobody's  ever  indicated  that I need to have
     seperate
     mod
     monitors  in  place. The Optimod on the AM and the exciter on my FM
     have
     pretty-colored Bouncy Bars, so I use them.
     As  a  small-market owner/operator, the money comes directly out of
     my
     pocket,
     and  I've not spent it there. I have, however, spent the money on a
     new
     Nautel to replace an old RCA, and trenched and pvc'd about 400 feet
     of
     new
     coax  out  to  the tower. Not afraid to spend money when I have to,
     but
     can't
     waste it, either.
     Dennis Switzer
     KKTY AM/FM
     Douglas, WY
     ----- Original Message -----
     From: "Burt I. Weiner"
     Sent: Wednesday, July 19, 2006 12:15 AM
     Subject: [BC] Speedometers on Cars. Do we need them?...
     > I don't think we speedometers in our cars either.  I rely on my
     > carburetor to not make my car go to fast.
     >
     > Burt

   Burt I. Weiner Associates
   Broadcast Technical Services
   Glendale, California  U.S.A.
   biwa at earthlink.net
   K6OQK