[AMRadio] New Topic - moniitoring modulation help please

Brett Gazdzinski b.gaz at comcast.net
Thu Nov 14 18:17:29 EST 2013

The cheap and easy way to do it is to hook a scope to an IF point in the receiver.
The r390 works really good for that.
If you get the signal into the receiver right, you can look at YOUR modulation on TX, and other peoples modulation on RX. The R390a was very good at doing that, both levels being very close.

I have that, plus a mod monitor (old ham fest buy), and the sdr-iq runs, if I over modulate, the spectrum display goes wide.

The sdr-iq also allows me to make sure my vfo has not drifted, even though its got a digital readout, its easier to look at the sdr display, that shows me where I am in relation to other signals.

The sdr-iq will run on almost any computer, and is not expensive.
it also makes for a good receiver.

You can also do tests like inject tone into the transmitter and adjust things for the lowest IMD and harmonics.
Easy to see on the sdr.

  ----- Original Message ----- 
  From: Bry Carling 
  To: amradio at mailman.qth.net ; Brett Gazdzinski 
  Sent: Thursday, November 14, 2013 7:20 AM
  Subject: New Topic - moniitoring modulation help please

  Brett's remarks were very positive and helpful... thank you!

  I have a question for the seasoned AM ops here. 

  Some of us (like me) need a little help.  I have read a lot of articles on how one goes about proper moniitoring of our AM signals, but I have never understood how to properly couple an RF sample into my oscilloscope and determine the %mod. etc. 
  I have also never felt comfortable trusting the mod meter designs I have seen. Most seem to involve some magic comparator that I am supposed to trust - like, "when this little light comes on you are at 85% mod and the other opne tells you you are hitting 100%." 
  How can I be confident?

  Those of you who have actually DONE this and are confident with your method and equipment please enlighten the rest of us with something simple enough and reliable enough to motivate us to either build or buy the necessary equipment to check our modulation. 

  Anyone needing help - I have available one extra frequency meter with digital readout to several places if anyone needs it.  It's a nice clean Haltronix - good to 600 MHz very cheap to anyone in this group, or I am open to trades,,,

  Please elucidate fully or point us to web sites that will demystify the AM monitoring process in easily uinderstood terms.  No deep calculus or excessive formulas if possible (grin!)

  I would not mind buying a commercial signal monitoring meter for my station if it was reasonably priced. 

  I think the real question some of us have is "How clean is my signal?"

  I could be running 200% modulation and stays within a 6 kHz bandwidth  if the signal is clean andI would be happy with that. I am thinking of my DX60B (or FT857D) + TenTec 422 setup that will soon be pumping some tall ship signals into the sky.

  73 - Bry AF4K


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