The APF feature of the K3.

[Geoffrey Mackenzie-Kennedy]

Hi Vic,

Do you know if any plot of the frequency response K3's APF exists, or any
similar data about its bandwidth at different levels of attenuation, and is
its response "peaky"?

I might have told you that as part of the ongoing development of my MkII
H-Mode receiver, I have for some time been considering various additions to
its audio circuitry - one of which is some form of APF.  The use of DSP is
not an option for this receiver, because any ADC that I can afford would
most likely ruin the 110db+  in-passband dynamic range of this receiver. Nor
is any form of Q-Multiplier

It has struck me though that an Audio Bandpass filter, whose bandwidth at
the 1db points is say a few Hz without a "peaky" response, might possibly be
a useful device to use as an APF rather than a filter whose response is
"peaky" -  when digging out signals in the noise floor. This is speculation
because I have not yet had the time to build and evaluate the performance of
an AF bandpass filter for this application.

73,

Geoff
GM4ESD

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[Barry N1EU]

see http://n1eu.com/K3/K3_apf.htm

Geoffrey Mackenzie-Kennedy wrote

Do you know if any plot of the frequency response K3's APF exists, or any
similar data about its bandwidth at different levels of attenuation, and is
its response "peaky"?

[Bill W4ZV]

APF was discussed extensively in August 2009 (check the archives) including a simulation of the exact FT-1000D APF analog circuit which I found and sent to Al W6LX.  Here's Al's simulation which was the model for the K3's DSP implementation of APF:

http://sites.google.com/site/ft1000apf/w6lxanalysisoftheapfcircuitintheft-1000

If you search online, you can find the FT-1000D Service Manual which has the analog APF circuit (less the front panel control pot VR8901-2 which is 1k ohms).  You must use the original resistor values, not those later changed in a Yaesu service bulletin (to address complaints of peakiness...which in fact is what makes it work).  Connoisseurs of APF that bought later "improved" FT-1000Ds quickly discovered its APF was not as effective as the original and reverted to the original "peaky" design:

http://lists.contesting.com/_topband/2000-03/msg00027.html

73,  Bill

[Bob K6UJ]

Barry,

Excellent plot, thanks !
This really shows why we need to tune slowly !

Bob
K6UJ




On Feb 4, 2011, at 4:12 AM, Barry N1EU wrote:

>
> see http://n1eu.com/K3/K3_apf.htm
>
>
> Geoffrey Mackenzie-Kennedy wrote:
>>
>> Do you know if any plot of the frequency response K3's APF exists, or any
>> similar data about its bandwidth at different levels of attenuation, and
>> is
>> its response "peaky"?
>>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/The-APF-feature-of-the-K3-tp5990251p5992342.html
> Sent from the [K3] mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> This list hosted by: http://www.qsl.net
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