[Elecraft] P3SVGA

[Wayne Burdick]

"You're both right," he mused, studying his own schematic (and inexplicably referring to himself in the third person).

The KNB3 *is* downstream of the pick-off point for the P3. But in the presence of very strong signals and with the KNB3 set to a long gate time, some of the gating artifacts could in theory back-propagate to the pick-off point, affecting the P3. Normally this effect would be highly suppressed because of the low impedance of the driving stage (the mixer post-amp).

Wayne
N6KR


On Aug 17, 2014, at 11:54 PM, Jim Brown <jim at audiosystemsgroup.com> wrote:

> Joe,
> 
> I don't want to be confrontational and I greatly value your engineering mind, but I'm quite certain that the wide K3 NB DOES affect the P3 display. I work a lot of JT65 on 6M, and there are several strong signals (not of overload magnitude) near me. The NB DOES create artifacts that result in multiple decodes, and corresponding stuff that is quite visible in the P3 display, and that is not visible when the K3 NB is off.
> 
> 73, Jim K9YC
> 
> On Fri,8/15/2014 2:35 PM, Joe Subich, W4TV wrote:
>> 
>>> I often study the screen of my P3, which DOES show reduction of noise
>>> when the wider NB is active. 2-4 dB is typical for the types of noise
>>> for which it is effective.
>> 
>> 2 - 4 dB may be due to upsetting the impedance at the IF feed but given
>> the circuit topology it is not possible for the NB to provide effective
>> blanking to the P3 with the noise gate *after* the IF pick-off point.
>> 
>> 73,
>> 
>>   ... Joe, W4TV
>> 
>> 
>> On 2014-08-15 5:13 PM, Jim Brown wrote:
>>> On 8/15/2014 11:29 AM, Joe Subich, W4TV wrote:
>>>> Jim, that information is incorrect.  The K3 NB can not possibly have
>>>> any impact on the P3 or P3SVGA as the IF pick-off is at the output
>>>> of the first mixer - *before* any noise blanker gate.
>>> 
>>> Joe,
>>> 
>>> I've never studied the schematic or signal flow in the regard, but I
>>> often study the screen of my P3, which DOES show reduction of noise when
>>> the wider NB is active. 2-4 dB is typical for the types of noise for
>>> which it is effective.
>>> 
>>> I appreciate the alert to the existence of the P3 NB. I last updated
>>> firmware about six months ago, and it was not in that version. It does,
>>> indeed, work pretty well.
>>> 
>>> 73, Jim K9YC