AW: [linrad] RE: Linrad and the microwaves

[guenter.koellner@xxxxxxxxxxxxxxxx>]

Hello Arie and other,

no, shurely I do not look on the S-Meter on my radio. It always shows different values. All my systems are aligned in such a way that the S-Meter displays a around S1 for noise. Believe me that I have many experience on VHF DX, I own a licence for nearly 20 years, beeing active on VHF for nearly all the time. Having done a lot on 2m, 70cm, 23cm, EME on 70cm and now on 23cm, MS on 2m and 70cm, having had many top places in VHF contests and so on.

It was my impression when I say that on the moon the noise is different than on terrestrial. I had many tries to use my 25Hz filter on the FT847 for terrestrial contacts, but I never found it useful. Completly different, on the moon it is phantastic. Yes, it has to do with the lower noise temperature in the main lobe of the antenna. But it is not only the noise temperature, it is also the noise by itself. Maybe terrestrial noise is more variable, maybe its just higher, at the end, something makes the narrow filter unusable on terrestrial.

Try it by yourself. Use FFTDSP, because it is the only software that really displays S/N. (Linrad does as well, but since I don't have it working completly until now, I cannot tell you). Search for a real CW signal of unknown content - not a continous carrier sent by a beacon - of around S/N of 5 dB or so. Try to decode it with your narrow filter. It will be hard. Then go to the moon and look for a signal of the same S/N, having the same contrast on the FFT waterfall, and you will see that it is easy to copy, much easier than the same signal strength on the terrestrial path. Could it be that the practical noise on terrestrial pathes leads to more ringing in the filters? I don't know.

According to SSB on the moon: If your system is just ready to do CW (3m dish, 1.2kW), and you just can do CW, how can you then explain that you can do suddenly SSB? I did a QSO with G4CCH, and DL4MUP was besides me, and CCH's signal was so weak, but nicely readable. I do not have recordings, otherwise I would have shown you.

This is experience and feeling, maybe believings, not measurements.

73, Günter, DL4MEA


> -----Ursprüngliche Nachricht-----
> Von:	Arie Dogterom [SMTP:pa0ez@xxxxxxxxx]
> Gesendet am:	Montag, 27. Januar 2003 14:33
> An:	linrad@xxxxxxxxxxxxxxxxxxxxxx
> Betreff:	Re: [linrad] RE: Linrad and the microwaves
> 
> Strange story,
> But I suppose you will tell us that the noise level=antenna temperature, is
> lower when looking up to the moon, than when looking at the horiziont. In
> the latter case your antenna temperature will not be lower than 145 K ( half
> of the antenna aperture sees the 290 K earth) and in practice your stations
> noise temperature will be in the order of 290 K, implying an S-meter
> deviation of S2 in 2,5 kHz bandwidth. Elevating the antenna, the noise
> temperature will be much lower and your S-meter will deviate less. That
> probably gives you the indication of weaker copyable signals. But in both
> cases you deal with the same thermal noise, so still S/S+N determines your
> reception.
> 73
> Arie Dogterom, PA0EZ
> 
> 
> 
> -- Original Message -----
> From: Koellner Guenter <guenter.koellner@xxxxxxxxxxx>
> To: <linrad@xxxxxxxxxxxxxxxxxxxxxx>
> Sent: Monday, January 27, 2003 12:55 PM
> Subject: AW: [linrad] RE: Linrad and the microwaves
> 
> 
> > Hello Leif,
> >
> > I do not know which kind of noise it is, I just mean that noise on EME is
> quiter than on terrestrial. Maybe, or surely, it is more constant. Another
> comparison: I did SSB QSO on the moon with signal strengthes that never
> would have allowed a SSB QSO on terrestrial pathes. Just when I remeber my
> only 23cm SSB with G4CCH, that signal on terrestrial would not even have
> been noticed.
> >
> > 73, Günter
> >
> > > -----Ursprüngliche Nachricht-----
> > > Von: Leif Ċsbrink [SMTP:leif.asbrink@xxxxxxxxxxxxxxxxxx]
> > > Gesendet am: Montag, 27. Januar 2003 13:05
> > > An: linrad@xxxxxxxxxxxxxxxxxxxxxx
> > > Betreff: [linrad] RE: Linrad and the microwaves
> > >
> > > Hi Guenter and all,
> > >
> > > > My experience with DSP processing on terrestrial pathes is, just
> > > > in a few words, that I think that there is much more background
> > > > noise, which cannot be handled by those narrow filters. If you
> > > > want to use narrow filters, you must have low background noise,
> > > > and this is the case at EME. I got this experience with Spectran
> > > > as well as with the 25Hz filter of my FT847.
> > >
> > > Interesting.
> > >
> > > Do you mean the "background noise" is of QRN type so it is smeared
> > > out by a narrow filter? I thought microwaves provided a nice
> > > white noise floor without impulse noise. Is there something else?
> > >
> > > 73
> > >
> > > Leif  /  SM5BSZ
> >


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