[TowerTalk] One DB

[David Gilbert]

Someone on the Towertalk reflector recently asked whether an additional 
one db of antenna gain was worth pursuing.  The answer, of course, was 
that it all depends upon how close you are to the noise level or QRM, 
but I thought it might be interesting to try to demonstrate that with a 
simple audio file.   So I recorded some noise from 80m, filtered out the 
really bad pops, and mixed in some CW at different levels.

For the purists, I'm not an audio expert and I won't guarantee any sort 
of precision in the result.  I simply used WinMorse to generate the CW, 
Total Recorder to record it at different levels (reference, minus 1 db, 
minus 2 db, and minus 3 db), and Goldwave to mix it.  The audio 
bandwidth of the 80m noise is arbitrary and changing it during playback 
will probably affect the overall readability, although in relative terms 
the demonstration should have some merit.  I also noticed some 
difference in effect (probably due to equalizer settings) between the 
various media players I tried so your mileage may vary.

I created two files, one where the CW pretty much stays above the noise 
and a second one where it almost dips below the noise.  The CW levels 
between the two files are about 1.7 db different (it just worked out 
that way) and the noise levels are about the same.  Unless I messed up 
you should be able to download them by right-clicking on the links below 
and saving the files to your hard disk.  They aren't contaminated with 
viruses, but if you don't trust me on that, don't download them.  Each 
file is about 280K in size because I was too ignorant to know how small 
I could make them without sacrificing quality, and too lazy to find out 
by trial and error.

http://www.mediamax.com/ab7e/Hosted/Signals_Comparison_A.mp3

http://www.mediamax.com/ab7e/Hosted/Signals_Comparison_B.mp3

My own personal conclusion is that one db can be noticeable but probably 
not a deal breaker, while two db can determine whether you make that DX 
contact or whether you're constantly asking for repeats during a 
contest.  And as one person stated it ... grab a db from the antenna, 
another from the feedline, and another from somewhere else and pretty 
soon it makes a big difference.  How much of that difference you want to 
spend a lot of money on is another matter ...  and is probably a 
function of how much of the time you operate near the QRN or QRM.

73,
Dave  AB7E


p.s.  MediaMax turns out to be a pretty cool site to store and share any 
legal file of any format.  They offer 25 megs of storage free, and 
upgrades from that aren't too expensive.  The site is excellently laid 
out and extremely easy to use.  Your files are normally protected and 
safe from anyone else, but anything you copy to your "Hosted" folder is 
available for download by anyone who knows the link.  You can even 
password protect individual "Hosted" files if you only want selected 
people to have access.  I'm not associated in any way with MediaMax, but 
I've looked around for sites like this for quite a while and haven't 
liked most of them.  This one seems to me to be an easy way for 
reflectees to transfer or share large files.