>> Since very weak signals (which is what APF is all about) are well below
>> the level that AGC action starts, when trying to dig out such a weak
>> station, it may be wise to turn off AGC altogether (provided you have
>> set the AF limiter beforehand).
It might be wise to ask Wayne and Lyle to consider activating the AF
Limiter when APF is turned on just to prevent a problem it a strong
signal jumps on top of the weak one we're trying to copy. It is not
much of a stretch to think that a local might call that weak UA0 on
160 or 5R on 80 while we're running "all knobs to the right" trying
to dig it out of the noise.
Looking at W8OZA's AGC test data, it appears that the audio output
can vary more than 40 dB from a -140 dBm (MDS) signal to a -43 dBm
signal (S9 +30 dB) depending on the user's selection of AGC slope
and threshold. If one adds another 10 dB of APF gain, a sudden 40
to 50 dB audio "shot" can be quite dangerous depending on the initial
listening level.
In addition, given reports of damage to the speaker amplifier with
sudden noise bursts with AGC off, enabling AF LIM with APF *might*
prevent some potential amplifier damage.
73,
... Joe, W4TV
On 11/6/2010 9:20 PM, Don Wilhelm wrote:
> Mike,
>
> The AGC works at the IF level, not the audio level.
> What that means is if you crank the AF gain way up to listen to a very
> weak signal, AGC action is probably not even started because the signal
> level is at or near the level of the band noise - In other words, the
> receiver is operation at "full gain, all stops removed".
>
> Under those conditions, if a very strong signal suddenly comes into your
> passband, yes, it will be loud simply because the AF Gain is advanced.
> Yes, the AGC will respond to that new signal - just how much depends on
> how you have the AGC menu parameters set. If it does cause an AGC
> response, it will reduce the gain of the receiver, and you will no
> longer be able to copy the signal at or near the band noise floor.
>
> So perhaps what I am saying is that everyone might run their AGC
> parameters so that all stations, no matter what their relative strengths
> will have the same audio level - that would cure the condition you have
> stated - but I do not really believe that is a good solution - for one,
> it will make band noise the same audio level as the signals - result is
> "noisy K3", and we have been there before.
>
> Myself, I prefer to be able to determine the relative strength of
> various signals "by ear" rather than "by S-meter" - that means the
> strong signals will have greater audio levels than weaker stations -
> that is just the way it is.
>
> Since very weak signals (which is what APF is all about) are well below
> the level that AGC action starts, when trying to dig out such a weak
> station, it may be wise to turn off AGC altogether (provided you have
> set the AF limiter beforehand). With AGC off, the Audio limiter is
> active to protect you from ear-shattering events such as a strong signal
> suddenly coming on frequency.
>
> An additional benefit to copying very weak signals with AGC off is that
> a strong signal coming on within the passband will not de-sense the
> receiver (as it would with AGC on), so you may be able to use the
> "filter between the ears" to continue copying the weak signal.
>
> 73,
> Don W3FPR
>
> On 11/6/2010 7:46 PM, Mike wrote:
>> Thanks Tom.
>>
>> Well, I kinda thought it shouldn't blast my ears that hard. Audio *WASN'T*
>> up too
>> loud for the signal I was after. Maybe I don't understand what AGC does.
>> That's why I
>> asked the questions I did.
>>
>> On 11/6/2010 6:21 PM, Amateur Radio Operator N5GE wrote:
>>> On Sat, 06 Nov 2010 18:04:18 -0400, Mike<n...@nf4l.com> wrote:
>>>
>>> Sounds normal to me.
>>>
>>> Audio up too loud and APF on, then a strong signal transmits on the
>>> frequency
>>> you are listening to....
>>>
>>> What do you think it SHOULD have done? You didn't say.
>>>
>>> Tom
>>> Radio Amateur N5GE
>>>
>>>> On 11/4/2010 9:48 PM, Mike wrote:
>>>>> I'm playing with the new APF, and trying to get a REALLY weak QSO to pop.
>>>>> I have the
>>>>> volume cranked up pretty good, and a REALLY strong station throws in
>>>>> their call. I
>>>>> thought my speakers had blown. Glad I wasn't wearing cans.
>>>>>
>>>>> My CONFIG:AF is 18, AGC = F.
>>>>>
>>>>> Was I doing something wrong? Anybody else experience this? Do we need/can
>>>>> we have
>>>>> better audio limiting?
>>>>>
>>>>> 73, Mike NF4L
>>
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