Re: {Collins} Receiver test data, Sherwood

Thanks guys, this was interesting but time to 


Scott Kerr
TrackerSoft, LP
Tech Support 214-237-7001
Sent from my iPhone

> On Sep 30, 2016, at 8:07 PM, Francesco Ledda <frledda@xxxxxxx> wrote:
> In SDR receivers, most of the distortion happens in the filter portion on the receiver, and it is very dependent on the AGC performance, being the channel dynamic range small. Reason is that trade offs are made to limit the number of bits of the channel and truncation is the way to go to reduce computing time. Having designed SDR receivers, I know first hand how challenging  the task is. Many compromises need to be made for cost and processing power reasons.    I have some Collins military type SDR radios, and they sound wonderful....
> Frank
> Sent from my iPad
>>> On Sep 30, 2016, at 18:43, Robert Nickels <ranickel@xxxxxxxxxxx> wrote:
>>> On 9/30/2016 4:27 PM, Don Jackson wrote:
>>> properly digitized audio does not introduce discernible noise or distortion, aside from quantization noise (controlled by number of bits). Of course, frequency response (set by sampling frequency and filter) must also be designed for the desired specification.
>> I agree, Don, and to your last point, it's important to consider the whole system - including the part that comes between the DAC and our eardrums.  Specifically  the audio stage in the receiver and that pretty matching speaker, aka what Bob Heil has been referring to as the "two dollar speaker in a a tin box".   Of course he's referring to modern radios, not a vintage Jensen driven by the class A audio of a Collins receiver.   But part of the difference that people who are calibrated to the sound of a modern radio is hearing in a Collins shack is AF rather than RF. Bob gave a great talk and demonstration on receive audio quality at the recent vintage SSB get-together at Jonesborough TN and I'm sure he'll be talking more on this subject on HamNation and in future presentations.
>> Bob's advice is simple:   use a good quality powered monitor speaker positioned at ear-level and feed your line-out audio to it by way of an inexpensive mixer that has at least three channel EQ.   This provides the ability to optimize the midrange frequencies that are key to speech articulation.  The bass and treble typically are centered around 12kHz and 80Hz - both way out of the range we hear from our ham receivers.   But a fixed midrange adjustment is typically in the 2 to 2.5kHz range, and Bob says if you look around you can find mixers where the center frequency of the midrange control can be shifted to your preferences.     So this is another way to make our classic radios sound great, especially to some not-so-new ears.   Kind of a new twist on the old ham saying "if you can't hear 'em, you can't work 'em".
>> 73, Bob W9RAN
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