[AMRadio] Use of an oscilloscope to monitor am audio

W5OMR/Geoff w5omr at satx.rr.com
Thu Apr 6 06:57:22 EDT 2006

-----Original Message-----

>From: W5OMR/Geoff 
>To each their own, I guess, but I personally prefer to monitor the envelope from a remote 'sense' antenna, that's fed into the front end of the o'scope. My sense antenna for my delta loop, is a 40m dipole. works great. 
>For 160, 75 and 40m, you'd need only a 20MHz scope.  
> doxemf at aol.com wrote:
>I found that the remote Ant method showed the actual radiated rf better than the internal link.
>  It suprised me that the my actual received signal showed slightly more output with a less than minimal SWR tuning. Tried all combinations of VKII final tuning and tuner manipulation (TenTec 1KW) but no matter what it showed a little more radiated output indicated by the external wire than proper tuning ended up with. Tuned up into a 50 OHM cantenna with low power and then went to the ant and dipped the SWR, then brought the drive up, dipped, dipped. Dipole was cut for 75 and the coax trimmed for the same. Might have been a fluke of my half flat top half zigzag ant but never quit figured out why this happened. Too late now. New QTH and no Ant yet.
>Bill KB3DKS/1 

My Dad was heard to say, many a time, that antennas seems to 'work 
better' (I believe he meant 'radiate better', or 'get out' better) 
witha  little SWR on 'em.

Personally, I've found that if I tune an antenna (and this is especially 
true of my bug-catcher) that I find that if I resonate the antenna just 
slightly -below- the operating frequency, the antenna seems to radiate 
slightly better, than if you were on the bottom side of the SWR dip. 

I can almost see the angles and vectors in my mind, all tangling 
together but I can't quite seperate it out enough to properly describe 
what I'm talking about.  But, on your mobile HF antenna, try this... say 
your desired frequency was 7.160Mc... tune your antenna for 7.155 for 
absolute minimum SWR and make a field-strength check at 7.160.  then 
re-resonate the antenna for 7.165, and see if the reading at 7.160 
hasn't dropped.  Why?  It's -only- 5kc!

It's like I can almost see it clearly in my mind, but it's just not 
quite clear enough to describe.  That happens a lot, to me.

73 = Best Regards,

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