[TenTec] OII V2.044A

[Rsoifer at aol.com]

Jerry,
 
Sounds reasonable to me.  I have no data on the effect of  fatigue.  I do 
know that in the good old days (1980s-1990s), when men   were men and EME was 
on CW, some of the best EME operators, like  VE7BQH, kept their rx 
bandwidths at 3 kHz or more, to minimize  ringing.  Others, like W5UN, kept theirs 
narrow.  Dave used a  QF-1A.  I used a QF-1.  Different ops, different 
strokes.
 
On another subject, I've found that the O II NB works best on 160 with a  
roofing filter of 6 kHz or more, regardless of where the DSP BW is set.   
Seems counter-intuitive, but there it is.  Tnx to k8IA for tipping me  off 
about it.
 
73 Ray W2RS
 
 
 
 
 
In a message dated 2/26/2011 9:16:59 P.M. GMT Standard Time,  
geraldj at weather.net writes:



On 2/26/2011 12:52 PM, Rsoifer at aol.com wrote:
>  Jerry, Lee, and others,
>
> It may be useful to draw a distinction  between digging weak signals out 
of
> the noise and improving the SNR on  stronger signals so they sound better.
> As we know, most of the  intelligence in (male) human speech is below 
about
> 2400   Hz.  The human ear is very good at disregarding higher 
frequencies,  so
>   passing the signal through a low-pass filter will make  it sound  better
> but, for most good operators, won't make much of  a difference in their
> ability  to dig it out of the  noise.

When the operator is fresh, yes. After several hours the  operator can 
become fatigued and then needs all the help the hardware can  give. But 
the brain extraction of weak signals from noise is sort of a  correlation 
process and if the noise bandwidth is too narrow, just like  correlation 
noise reduction in a DSP it works less well with narrow band  noise.

Same for CW. One year at FD at our club station the CW rig was a  TS-430 
owned by a ships sparks bought overseas with a factory narrow CW  filter. 
That radio didn't seem to have the option of selecting the filter  or not 
for CW and so it was always in the circuit. So I couldn't switch to  a 
wider filter and that filter rang enough on noise and was narrow enough  
the noise had a pitch to it, so copying CW I had a constant tone to  
discriminate against which wore me out in less than 4 hours of  operating.

In my FT-857D, I've found the audio DSP CW filters do  nothing to improve 
S/N of a CW signal below the noise level or to make it  easier for my 
brain processing to do it, but the Collins mechanical CW  filter does 
improve the S/N of a CW signal below the noise. The difference  between 
copying and not copying on long VHF paths.

73, Jerry,  K0CQ
>
> 73 Ray W2RS
>
>
> In a message dated  2/26/2011 6:16:09 P.M. GMT Standard Time,
> geraldj at weather.net  writes:
>
> That's  where I find my passive speaker filter  shines. It passes no audio
> section  noise and no IF noise, an few  DSP HF artifacts.
>
> A fundamental of  receiver design is  that selectivity works best as close
> to the antenna as  possible.  Unfortunately that ignores the noise
> contributions of all the   stages after that. The typical product detector
> is double sideband so  the  IF noise of the image is there along with the
> signal and the  RF noise that  passed through the filter plus the same
> sideband  noise much wider than the  filter that was up front. Receivers
>  would benefit from having a SSB filter  at the product detector, but  I
> know of only one design that way, called  the Hohentweil, a  2m
> transverter kit. Then they would benefit from making  the  audio output
> stage, often essentially a power op amp into an  active  low pass filter.
>
> In tube receivers a simple  capacitor from audio output  tube plate to
> ground combined with  the tube and the audio output  transformer to make a
> rudimentary  low pass filter. In the 75S-3B, it was  effective enough to
> make  using 2125/2975 tones for 850 shift RTTY (and for  all recorded
>  history, the standard tones for 850 shift RTTY due to an  AT&T  standard)
> difficult until the capacitor was removed from the   circuit.
>
> 73, Jerry, K0CQ
>
> On 2/26/2011 11:57  AM, kc9cdt at aol.com  wrote:
>> I think one of the reasons the  Drake R-4B, Hallicrafters SX-117  and
>> many others are beter  in a noisy condition is simply they do not  have
>> all the high  frequency respnse in the audio, or maybe it is the  tube
>>  amp??. I wish there was a HF cutoff on the OII, full EQ like Bob   Heil
>> recommended day one to TT way back may have   helped.
>>
>> Interestng...last nght, on 40 I was working a  really  nice guy in St
>> Kitt. There was quite a lot of QRN, He  was just above  the noise floor
>> I found that if I used the  old Hallicrafers SX-117 to  receive
>> him...copy was more  clear!!!!
>>
>> OMG, Maybe we  need to go back to the  older stuff (I have both) Unless
>> of course it  is contesting  at a high level...where you need lot of 
speed
>>
>> I   use the Collins S line&   KWM-2
>> Drake C line (all  Sherwood  mods)
>> Halli SX-117/HT-44
>> Halli  SX-115/HT-32B
>>
>>   Along with the OII of  course.....
>> 73,
>>   Lee
>>
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