[Premium-Rx] Subject: Re: 100kHz converter outputs - more

[John Graham]

Hello Nigel,

Yes, you may well be right; that certainly makes more sense, and the adjustment procedure does call for obtaining notches at 3 specific frequencies in the input filter. Unfortunately my copy of the manual is missing p13 with the adjustment of the output filter, but the plot in Fig.4 does show a notch at 467kHz and about 40dB attenuation above that

thanks,

John G.



Message: 4
Date: Tue, 17 Aug 2010 05:44:06 EDT
From: GandalfG8 at aol.com
Subject: Re: [Premium-Rx] 100kHz converter outputs - more
To: premium-rx at mailman.qth.net
Message-ID: <d0d6f.10ae783e.399bb3e6 at aol.com>
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In a message dated 17/08/2010 10:01:37 GMT Daylight Time,  
john.graham02 at btinternet.com writes:

I could  understand a bit of headroom to avoid phase shifts at the edge of 
the  passband, but this seems like serious overkill - the RA1792 LPF really 
is flat  to 200kHz!
----------------------

Hi John
 
It may be necessary to consider the function of the input and  output 
filters in the RA1792 100KHz module slightly differently.
 
Although they obviously have to pass 455KHz and 100KHz, in the case of the  
input and output filters respectively, they also have the  very important 
function, quite possibly their pimary function, of  protecting the receiver 
from the 555KHz local oscillator signal generated on the  100KHz interface 
board.
 
If a relatively narrow LC 100KHz bandpass filter had been used  for the 
output filter, or a high pass filter with roll off very close to  100KHz, it 
would have been much more difficult to control the out of band  performance at 
over five times the design frequency.
 
regards
 
Nigel
GM8PZR