Jeffrey, and all --
I think Roger solved the "problem" with his email to the Linrad
reflector, copied at the very bottom of this message.
He has found no significant difference in JT65 *decoding ability* with
Linrad and with a conventional receiver. What he does see is different
*S/N levels* reported by WSJT. This I can easily believe.
Unlike Linrad, WSJT makes no attempt at being a useful laboratory
instrument. It uses many quick-and-dirty approximations to get numbers
peripheral to its real task of facilitating weak-signal communication.
It has been a while since I thought about it, but I think the reported
S/N numbers could easily depend on the total bandwidth of the audio
signal being analyzed, and probably even on the bandpass shape.
There is still this to consider: with xpol antennas the Linrad receiver
should do better (on average) at JT65 decoding than any receiver
connected to either the H or V elements alone. If the received signal
is at 45 degrees, the polarization-matched Linrad advantage should be 3
dB. If this can't be observed, isn't it true that something else must
be wrong?
-- Joe, K1JT
Jeffrey Pawlan wrote:
I was correct that Roger is not able to use the WSE hardware without linrad.
It was a surprise to find that he is getting better IMD performance with the
FT1000MP than with the WSE receiver.
---------- Forwarded message ----------
Date: Wed, 18 Oct 2006 01:01:03 -0400
From: ROger Rehr <[EMAIL PROTECTED]>
To: Jeffrey Pawlan <[EMAIL PROTECTED]>
Subject: Re: Linrad and WSJT and EME
Hi, Jeffrey,
Thanks for the note!
You are correct, and it is #1 and #4. As it was stated:
---self-quote
I had the two systems [transverter/FT1000/WSJT and WSE/Linrad/WSJT] in
running in parallel, each feeding a soundcard and WSJT on a separate
computer.
---end self-quote
Translation of my original post as copied directly above from the first email:
System 1:
transverter to FT1000 to WSJT on computer #3
System 2:
WSE to Linrad on computer #1 to WSJT on computer #2
As regards the other two possibilities, it is not possible to do WSE
directly to WSJT as WSE puts out a 90 kHz wide signal [0-90 kHz]. You
need to convert the desired portion of this 'low IF' to audio to feed
into WSJT. That is [part of] what Linrad does. So #2 is not possible.
Feeding audio from a conventional receiver to Linrad not something that
would have a practical use for me. I can tell you that with WSJT
Linrad would not add value in this situation unless there were pulse
noise that only Linrad could remove. I don't usually have this problem
at my country location [and noise was not a problem at all this
weekend]. WIth CW you can get 'some' benefit from Linrad with input
from a conventional receiver by virtue of Linrad's nice narrow filters
and noise blanking, but only the noise blanking remains as a benefit
with WSJT.
The result really should not be extremely surprising, although it is
somewhat surprising and that is why I reported it. Also I reported it
because I was a bit disappointed. I had expected Linrad to enable
better decoding and provide better dB values, and it did not.
There are multiple differences between the two systems [conventional
and WSE/Linrad] that might explain the result. First of all, it is
difficult to pick the 'right' polarization angle on a weak wsjt signal
in a wide USB type passband with Linrad. Yes if you have lots of time
you can get it right. But in trying to quickly work QSOs in a contest
it is difficult. Linrad CANNOT automatically get the polarization
angle right most of the time on a WSJT signal because the passband is
wide, and there is most often a stronger unwanted signal in the
passband that WSJT is smart enough to ignore, but Linrad is not. It is
much easier to set polarization angle on the fly with just H and V
choices and a conventional receiver.
Secondly, an FT1000MP with addon roofing filter such as I have
installed is much less bothered by strong signal interference than WSE,
which by design has a wide input passband [2 MHz]. This is often a
MAJOR advantage of the conventional system at my location where the
noise floor of Linrad can be raised in the upper third of the 90 kHz
passband by 5-10 dB not by pulse noise, but by IMD.
I KNOW these two items are important. There is also the [speculative]
possibility that something in the way Linrad outputs the audio after
its processing makes the signal less suited to the analysis that WSJT
does. I haven't analyzed the quality of the audio output of Linrad and
compared it to the conventional receiver. It would not be surprising
to me if this was the case. Linrad was made for human reception, not
computer decoding. Is the WSJT observation a case of unintended
consequences of the algorithms used in Linrad?
Finally, please note that I specifically said [self-quote again ;) ]:
-----I got equal decoding on the two systems-----
What I saw was a difference in the dB readings, not a difference in
decoding ability. That was absolutely clear in my post and means that
I did not see a practical difference in the ability to make QSO's
between the two systems.
HOpe that helps.
I must go to bed now. It is one am and I must be upat 6 for work ;(
Roger Rehr wrote:
> Hi, Joe,
>
> I had informally 'thought' I noticed this over past couple of years but
> didn't 'look for it' in any systematic way. This year, I didn't write
> down numbers, but planned before the contest to consciously note if this
> was in fact the case: that the LT2S Mk II and the FT1000MP outdid the
> WSE boxes with WSJT.
>
> This past weekend when I looked for this effect systematically, I
> noticed that the conventional system did do better in that the dB
> numbers were pretty consistently 2-4 dB better [less negative] with the
> conventional system than with Linrad. But the two systems performed
> equivalently in terms of decoding the signal.
>
> It might be that this was due to not setting the polarization angle as
> well with Linrad as I did by just selecting H or V with the FT1000 setup.
>
> Again, for me it was a difference in the 'dB' indication, not a major
> difference in decoding. In the past I had thought that the Linrad chain
> did an inferior job of decoding. But when I specifically looked for
> that, it didn't pan out. I had with each system one or two instances
> where it missed the decode while the other one picked it up. But there
> was no systematic difference in this regard by my informal study.
>
> I hope that helps. It is what I remember now, and what I see that I
> typed in my email to the list when things were fresher in my mind, so I
> think it is a true reflection of what I noticed.
>
> Have a great week, and
>
>
> 73,
>
> W3SZ
> Roger Rehr
> http://www.nitehawk.com/w3sz
>
>
> Quoting Joe Taylor <[EMAIL PROTECTED]>:
>
>> Ermanno, Roger, and all --
>>
>> One thing about your recent posts concerning Linrad and WSJT surprises
>> me. You both say that Linrad helps you to find JT65 signals, but the
>> signals seem to be decoded better when received by a conventional
>> receiver.
>>
>> I have certainly not noticed this effect, but my on-the-air experience
>> with Linrad is still minimal. I have not done any explicit side-by-side
>> comparisons. However, I have a hard time trying to understand what the
>> origin of such an effect could be. I think it's important to find out,
>> and I would welcome any additional information, reports of further
>> measurements, detailed documentation, etc.
>>
>> -- Joe, K1JT
>>
>> PS to Ermanno: I will send you my parameter files soon. Very busy over
>> the past several days, hihi.
>>
>> #############################################################
>> This message is sent to you because you are subscribed to
>> the mailing list <linrad@antennspecialisten.se>.
>> To unsubscribe, E-mail to: <[EMAIL PROTECTED]>
>> To switch to the DIGEST mode, E-mail to
>> <[EMAIL PROTECTED]>
>> To switch to the INDEX mode, E-mail to
>> <[EMAIL PROTECTED]>
>> Send administrative queries to <[EMAIL PROTECTED]>
>>
>
>
> Roger Rehr
> W3SZ
> http://www.nitehawk.com/w3sz
>
#############################################################
This message is sent to you because you are subscribed to
the mailing list <linrad@antennspecialisten.se>.
To unsubscribe, E-mail to: <[EMAIL PROTECTED]>
To switch to the DIGEST mode, E-mail to <[EMAIL PROTECTED]>
To switch to the INDEX mode, E-mail to <[EMAIL PROTECTED]>
Send administrative queries to <[EMAIL PROTECTED]>
