MONITORING YOUR MODULATION

I’ve been doing a bit of AM operating of late.  This vintage mode if fun to operate and sounds great when the band conditions aren’t too noisy.  I’ve also been repairing and tinkering with some old transmitters as mentioned in other posts.  One of the highest pursuits of the AM op is to achieve great audio.  Many will go to great lengths to buy studio rack gear with pre-amps, compressors, limiters, and EQ.  Top off all this hamsexy rack gear with a big old boom mic!

The other part of the equation is to properly adjust the audio modulation.  It’s not as simple as watching the ALC meter like on SSB (although it does help).  A first step is to look at the RF waveform on an oscilloscope.  You want to verify that the wave isn’t flat topping.  A modulation monitor can be used to view the modulation percentage.  Combine these two together and you get the AMM-SD1 by Radio Engineering Associates.  This slick device connects into the feedline and runs in software on the computer.  It’s pretty much real-time display shows the RF waveform and the negative and positive modulation percentage peaks.

Seemed like this might be a worthwhile investment for the shack…like I even need an excuse to by cool shack gear!  So far it’s confirmed that my AM audio is clean with positive peaks over 120% and negative peaks right at 100%.  Right about where it needs to be.  I’ve also used it to detect that the Ranger II I’m working on is in need of further inspection.  The positive peaks only hit about 40% before the stopping point when negative peaks hit 100%.  I never would have found that without the monitor unless trying to make a contact and some OM tells me my signal is crap.

This monitor has already proven to be an asset to my radio operation.  I just wanted to share it with my followers and encourage people to give AM a try if you like a little more than UR 59 OM, QRZ.  There are frequent AM operating events throughout the year, so there’s no excuse not to lay down some carrier and chat it up.

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Categories: Activities, Amateur Radio, Projects, Uncategorized | Tags: , , , , , , | Leave a comment

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