[AMRadio] Audio Limiter for AM HAM TX


Rob Atkinson ranchorobbo at gmail.com
Tue Aug 19 12:07:01 EDT 2014


There are basically two kinds of limiters.  One is the studio limiter
that has a slower attack and is not an AM broadcast type limiter.  The
classic version of that is the old UREI 1176.  In the Orban blue panel
line, the 422.  So you need to be sure to get a limiter that is
specifically described as a broadcast limiter, i.e. a modulation
limiter if you want the fast aggressive limiting that doesn't let any
high peaks get by.  I have not had experience with all of the old
limiters out there but assuming you can't afford anything pricey like
an Optimod, then the CRL line of PMC boxes are good.  PMC 300, 400 and
450.  PMC stands for Peak Modulation Controller.   These used to be
relatively inexpensive but the prices seem to be creeping up.   The
Optimod is actually a multi-band compressor and limiter in one box.
Inovonics had or has a limiter, the model 222.  Less often seen are
the Dorrough DAP310, and Gregg Labs and Texar limiters and BL
Modulimiter.

But a word of caution:  Vintage ham AM rigs were not designed to
handle compressed limited audio.   The mod. iron in your Desk KW may
be better off with a mic into the rig and the op keeping an eye on the
carrier with an oscilloscope.   You may have to modify the rig before
you start driving it with heavily limited audio.

73

Rob
K5UJ

On Tue, Aug 19, 2014 at 10:12 AM, pete zilliox <pete at zilliox.net> wrote:
> Forgive this query if it's been discussed many times before....I've looked
> on ebaY (yeah I know) for a cost effective simple inexpensive audio chain
> limiter to use with my Symetrix 528E voice processor that drives my EF
> Johnson Desk KW AM transmitter.  I want to protect the very old Johnson
> high level modulation transformer from over modulation.  I'm totally over
> whelmed with way too many options on ebaY.  I am only looking for a single
> channel limiting function in a reasonably priced box.  I currently use a
> Nady active (vacuum tube pre-amp) broadcast mic to the 528E followed by a
> Dorrough  Loudness meter in parallel to a line going to the W2IHY 600ohm/Hi
> Impedance variable level control feeding the Ranger exciter.
>  Recommendations for such an inline limiter, anyone?  Thanks Pete - K5PZ
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