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Date: Fri, 11 Dec 2009 14:18:29 +0100
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Thread-Topic: LF: "Gain" between qrss3 and qrss10?
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From: =?iso-8859-1?Q?Stefan_Sch=E4fer?= <schaefer@hst.tu-darmstadt.de>
To: <rsgb_lf_group@blacksheep.org>
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Subject: AW: LF: "Gain" between qrss3 and qrss10?
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Reply-To: rsgb_lf_group@blacksheep.org


Thanks Johan for the qualified answer!
With the receiver bandwidth, do you mean the bandwidth of e.g. the argo pr=
ogramm or of the real receiver, say the ic706?
I use a K2 with a bandwidth of 50Hz (not very sharp edges), which is relat=
ively norrow compared to the most standard CW filters in standard HF-TRXs.=
 Since I can=B4t reduce it even more and the others as well, it would be=
 no advantage to reduce the speed. So I think you mean the bandwidth of e.=
g. argo? Right?
Tnx!=20
Stefan/DK7FC =20

-----Urspr=FCngliche Nachricht-----
Von: owner-rsgb_lf_group@blacksheep.org [mailto:owner-rsgb_lf_group@blacks=
heep.org] Im Auftrag von Johan H. Bodin
Gesendet: Freitag, 11. Dezember 2009 13:55
An: rsgb_lf_group@blacksheep.org
Betreff: Re: LF: "Gain" between qrss3 and qrss10?

Hi Stefan,

> Or isn't it possible to give such a relation?

Yes, it is not only possible, it is in fact quite simple:
When the speed is reduced by a factor K, the information bandwidth is
also reduced by the same factor. This allows you to use a receiver
bandwidth which is K times narrower without missing any information. The
nice thing is that the noise power passing through this bandwidth is
also K times smaller - The S/N ratio has improved K times (or 10*log(K)
dB if you prefer). In other words, you can reduce the TX power by the
same factor K and still enjoy the same SNR (if RX BW is is also made K
timer narrower).

In visually received QRSS, the receiver bandwidth is equal to the RBW,
the "resolution bandwidth", which is approximately equal to the FFT bin
width (one pixel on Argo).

QRSS30 is 10dB more efficient than QRSS3, in theory at least.

73
Johan SM6LKM

----

Stefan Sch=E4fer wrote:
> Dear LF,=20
> Does anybody know about the "gain" between QRSS3 and QRSS10 or QRSS30?=
 I mean, if the noise in both cases is equal, how much can I reduce my tx=
 pwr when switching from qrss3 to qrss10? Or isn't it possible to give suc=
h a relation?
> And: Was there ever a TA QSO in QRSS3?
> I am new on the reflector, sri ;-)
>=20
> Stefan / DK7FC
>=20
>=20