Re: LF: OPERA Question

[M0FMT <m0fmt@yahoo.co.uk>]

Hi again Graham

 

"....... Narrow IF filters are not desirable and reduce the performance of the demodulator , better simply use SSB filter.........."

 

Yes I found that out in use. I was using my both CW filters and the IF shift to crunch down to 200Hz results much inferior to just running the wide SSB filter 2.4kHz!

73 es GL Pete M0FMT IO91UX

From: Graham <g8fzk@g8fzk.fsnet.co.uk>
To: rsgb_lf_group@blacksheep.org
Sent: Tuesday, 10 July 2012, 16:56
Subject: Re: LF: OPERA Question

Yes  , with  one correction  , ( for  audio  drive)

The  carrier placement  routine, when  Tx is  selected  , scans  the Rx audio  band and selects  the  lowest s/n  spot  frequency in that  range

So  if you  are  using  a  transverter  (or on frequency  exciter  )  then the TX frequency  is  decided by the  audio  drive  frequency  inside the limits  (red-lines)  for  that  mode/speed

If  using  manual  frequency selection, then  a Tx  frequency  must  be selected, that  will  produce a  carrier/hetrodyne  that  falls  inside the audio pass  band  (red-lines)  defined  by convention as  'dial  set  usb frequency'

Changing  the  speed  also  requires a  change  of  frequency  to  place the carrier  inside the  correct  filter , automated  if  using  audio-drive.

Narrow  IF filters  are  not  desirable  and  reduce the  performance of the  demodulator  , better  simply  use  SSB  filter

NB :  The  pass  band  edges  are  quite  sharp  , so  ensure  you  are 'inside' and  not  'on the  line'  or  you  may  fail  to  decode  ....... also  tx / rx  frequency  alignment  may  place you  out  side ....  i

Keying  , recommended  that  the  TX be  held in 'tx'  , to  prevent  tx/rx change over  times  from  altering  the  keying  times .... not  100%  a problem , but  to  enable  decodes the  lower levels  , time +/-  and frequency  +/-  need  to  be as  close to the  generated values  as possible


GL ..73 -G..


--------------------------------------------------
From: "Albert" <westberg@xs4all.nl>
Sent: Tuesday, July 10, 2012 2:58 PM
To: <rsgb_lf_group@blacksheep.org>
Subject: Re: LF:  OPERA  Question

> Stefan,
>
> Download the Opera program. In the waterfall you will see two red lines, put the cursor on the lines and read the frequency (upper left window of the waterfall display)  Op4 differs from Op8 etc a frequency within this band is the input of the USB TX so 477kHz + (a frequency between the red lines). When using CAT control Opera will choose a not occupied freq. in the appropriate pass band.
>
> 73, Albert
>
>