Topband: Skimmer calibration

[Tom W8JI]

Since no one likely knows the gain of a reference antenna within a dB or so, 
splitting hairs doesn't matter.

Ten dB would jump right out, while 3 dB might get lost in the QSB.

When I was comparing high dipoles to verticals on 160, I collected reports 
for about a year. It was thousands of reports.

I probably could have done it in a week or two with skimmer, but then I 
would have had to repeat it for seasonal changes. I'm sure a good test 
protocol using skimmer could be worked out.


----- Original Message ----- 
From: "Jim Brown" <jim at audiosystemsgroup.com>
To: <topband at contesting.com>
Sent: Monday, August 18, 2014 12:47 PM
Subject: Re: Topband: Skimmer calibration


> 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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