[AMRadio] Audio Limiter for AM HAM TX


Rob Atkinson ranchorobbo at gmail.com
Tue Aug 19 17:48:59 EDT 2014


On Tue, Aug 19, 2014 at 12:39 PM, GRANT YOUNGMAN <nq5t at tx.rr.com> wrote:
> The current gold standard in the ham community appears to be the Inovonics 222.  The most advantageous thing about it is that the gyrator-based LPF can be modified to limit AM bandwidth to something under the NRSC limit for ham use (a bezillion resistors, but not too bad).
>

I think Inovonics will sell a modification kit and instructions on how
to change the cutoff frequency.

> The CRL PMC-series limiters are also very effective.  Example would be the PMC-450.
>
> Both of those boxes seem to go in the $400-450 range give or take, although you can probably find a CRL PMC box for less.
>

It pays to look around.  I once got a PMC400 at a hamfest for $20.
It just needed some cleanup and a couple of weeks running it.   I also
found a PMC450 on ebay for $250.

> Even a CBS Volumax/Audimax would work ok -- just make sure the Volumax is an AM limiter and not an FM version.  I would recommend the use of the Audimax leveler with the Volumax.  eBay prices on these seem ridiculous to me, though, given their age.  I used to use a set of these on a Globe King, and they worked fine.
>

I forgot about the CBS Labs gear.  Thanks for mentioning it.   They
show up on ebay also.

The problem with setting up a low pass filter in a limiter like the
Inovonics 222 is that your bandwidth is fixed at whatever cutoff you
choose.  If you prefer to vary it with conditions and bands, then it
is better to have the limiter running wide open, and select a
different cutoff elsewhere.
There are passive filter designs.  I simply cascade a pair of
equalizers, each with 15 dB boost/cut to get enough high frequency
attenuation.

Jay, I think we'd all love to try a 9000 or 9100 : )

73
Rob
K5UJ


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