Topband: Skimmer calibration

Jim Brown jim at audiosystemsgroup.com
Mon Aug 18 12:47:58 EDT 2014


On Mon,8/18/2014 4:53 AM, Tom W8JI wrote:
> A live comparison of S/N ratio or relative level over time is with 
> very few exceptions an excellent comparative test. It is much more 
> accurate than S meters or absolute levels without a comparison 
> reference. As such, the RBN is a great tool for evaluating systems. 

Yes. BUT -- my experience has been that I must average hundreds of data 
points to get meaningful data. The reasons are simple -- we must contend 
with QSB, and as Tom noted in another post, nulls in the patterns of 
antennas at both ends. A few years ago, I tried to compare two 160M 
antennas using JT65 and W6CQZ's JT65 RBN. On a good night, I would see 
reports from 3-4 stations east of the Mississippi. I alternated between 
the two antennas for hours, putting the reports in a spreadsheet, and 
studying the data. Modelling predicted differences of a few dB, and I 
never found that the data was good enough to confirm the models.  The 
antennas are passive arrays of fairly tall verticals of a quarter wave 
or less, so there are no vertical nulls in their pattern. I can clearly 
hear their directivity on RX, but their gain is what I was trying to 
confirm.

73, Jim K9YC




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