Hi again Tom,
I found a real expert in this field: AE0M works in the hearing aid industry
and is well versed in the human hearing field. Tony told me that for
unrelated voice applications (such as telephones) there probably needs to be 2
or 3 dB difference to be able to say that one is louder than the other.
However, for a "trained ear", and that probably includes all of us, it is very
possible to distinguish strength differences betweens two tones in a noisy
environment with only a few tenths of a dB difference. I that means it really
does makes a difference between running 100W and 150W after all. Guess I'm
lucky no one took me up on that challange... hi
As you said, pitch and timing also play a big part in determining who gets
called, but I was wrong about the hearing sensitivity issue.
73, Al AD6E
In a message dated 8/12/98 5:23:47 PM EST, n4kg@juno.com writes:
<< Subj: Re: NAQP Power
From: n4kg@juno.com (T A RUSSELL)
To: AD6E@aol.com
Thanks for the note Al.
Yep, the two signals will still be 1.7 dB apart. I expect that
who you go back to will depend more on timing, pitch, and
whose call you can ferret out using your aural selectivity.
I remember hearing very weak stations calling that I just
could not get to because there were too many stronger
stations who called each time I finished a contest QSO
and I kept hoping that no one new would show so that I
could copy the weak guy so yes, you can hear quite a
ways down below the AGC limited signals. Definitely
not a case of "capturing" like with FM.
73, Tom N4KG
On Mon, 10 Aug 1998 02:19:29 EDT AD6E@aol.com writes:
>In a message dated 8/8/98 10:45:18 PM EST, owner-cq-contest-
>digest@contesting.com writes:
>
>> From: n4kg@juno.com (T A RUSSELL)
>> Subject: Re: [CQ-Contest] NAQP Power
>>
>> On Fri, 7 Aug 1998 11:03:12 EDT PaulKB8N@aol.com writes:
>> >
>>
>> >They say you can't hear the difference between 100W and 150W.
>> >Hogwash! It is
>> >not hearing that counts, since most operators use AGC. 150W will
>> >"capture"
>> >the AGC over 100W every time, no matter how loud you "feel".
>> >
>> >Paul, KB8N
>> >
>>
>> Paul is right-on about this. AGC keeps the audio output constant
>> by reducing receiver gain. The strongest signal dominates.
>>
>> The dB difference between 150 W and 100 W is exactly the same
>> as the dB difference between 1500 W and 1000 W, 1.76 dB.
>> (Power gain = LOG ( P2 / P1 ) in dB).
>>
>> de Tom N4KG (receiver design engineer in my other life)
>
>
>Hi Tom,
>
>I agree that the stronger signal will drive the AGC, however the "weaker"
>signal will still be only 1.7 dB below it. Thats assuming the AGC stays
>linear, of course. If it doesn't, then the two signals compress to the
point
>where there is no difference.
>
>The question I was trying to raise is "which station would you go back to?"
.
>. . . or can you really hear the difference in your ear? To turn the
>question around, how much power difference is needed to be
>significant? This
>isn't a matter of RX design, rather human hearing ability. Bell Labs did a
>study many years ago, and as I remember it they found that typical telephone
>users can't hear a volume difference of less than 3 dB. Of course
>thats voice
>based, not CW. I really don't know what my sensitivity is. Maybe its
>worth an experiment?
>
>I'm also a radio engineer. I've spent most of my years designing digital
>microwave links. I do the baseband and modem parts, not much of the
>microwave stuff.
>
>73, Al
>AD6E
>
>>
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