[TowerTalk] Minimum Discernible Difference

[Jim Brown]

Hi Dave,

I didn't listen, but I did read, and I think both your methodoloy and 
conclusions make sense. One thing I WOULD change though is to work in the 
WAV format rather than MP3. 16 bit 8 kHz is enough. The compression to make 
MP3 files adds digital artifacts that could cloud the results. In essence, 
compression removes bits that the algorithm doesn't think are important, 
then, on playback, guesses at what bits were deleted and reinserts them. 
That happens each time you do something, so it happens when you record the 
initial files and play them to mix with each other, and it happens again 
when you save the resulting file and play it back to listen. 

FWIW -- I just finished a new 160M antenna that NEC predicts should be good 
for 3dBi at an elevation of 15 degrees. Initial comparisons of groundwave 
signals at several locations with the new antenna and the old one suggest 
that 2dB is more like it. The old one is an 86ft vertical with 100 ft of 
top loading over 70 radials.

It's an interesting antenna -- my SteppIR is on a 118 ft tower, with about 
4 ft of additional mast. NEC thinks the tower plus mast plus SteppIR is 
long enough to act as a reflector for a wire that slopes away from the 
tower at about 30 degrees or so. No connection to the tower, and it's held 
about 5 ft away from the tower at the top. I've added 4 elevated radials 
(ala N6LF) to both the tower and the feedpoint of the wire. The azimuth of 
the slope is about 80 degrees. And, of course, I've rigged a second version 
of this antenna on the other side of the tower to get gain toward VK and 
JA. It's a pretty broad pattern, +/- 55 degrees for 1dB down from the peak, 
and about 7dB F/B. 

I'd appreciate comparative reports between this antenna and the old one, 
especially within the main lobes, and especially with the voltmeter 
function in the K3. They're rigged so I can switch instantaneously.

73, Jim K9YC

On Mon, 23 Aug 2010 11:15:46 -0700, David Gilbert wrote:


>I've added a page to my web site covering some investigations into how 
>much difference in signal strength might be noticeable in weak signal 
>and/or contest conditions, with several audio files included as 
>illustration.  Please don't consider any of it to be authoritative since 
>I am not an audio professional, but maybe some of it will be useful to 
>someone.  If anyone has suggestions for different comparisons, please 
>let me know.

>http://www.ab7e.com/weak_signal/mdd.html

>73,
>Dave   AB7E


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