Re: AW: LF: "Gain" between qrss3 and qrss10?

[Rik Strobbe <rik.strobbe@fys.kuleuven.be>]

Hello Stefan,

> If the "gain" or
> better said SNR between qrss30 and qrss3 is 10dB, so can I do a QSO to VK
> with 1W TX Power and an antenna efficiency of 1/1000 if I choose
> QRSS10000000000? That?s a litte jokingly formulated but you know what I
> mean. In other words, where are the limitations of this rule?
In theory: yes
In real world: no
There are practical limitations such as:
- assuming that a minimal QRSS QSO takes 15 minutes at QRS3 it will take
50 minutes at QRS10, 150 minutes at QRSS30 ... 600 minutes (= 10 hours)
at QRSS120 and 50000000000 minutes (almost 100 centuries), meaning that
your grand-grand-grand-grand-...-grand child will have to finish the QSO
;-)
- also the frequency stability of TX and RX and dopler effects in the
ionosphere will put a limit to the bandwidth and thus to the meaningful
dotlength

> In CW I think that rule cannot
> be valid because a dot in CW (say 20wpm) is much shorter than 0,3s but to
> my experience the ?gain? compared to qrss3 is not even 10dB. Furthermore
> a PC must be seen as a source of QRM, especially when connected to the
> antenna system (e.g. for switching a tx relay with the qrs-programm) and
> RX (even when using a insulating transformer for the AF), and so it
> always brings a ?negative gain?, even when one uses 10s of ferrite
> cores?   
Tests by DK8KW, W1TAG and others
have shown a 10 to 15dB difference between QRSS3 and regular CW. Such
tests are always a bit subjective (ie. compare a visual signal with a
auditive signal), but it more or less confirms the theory.

> And: I always thought of the
> energy "waste" when applying 1kW (before 6 yrs when I became
> qrv with a much worse antenna) to the antenna and pumping 999,9W into the
> earth. But when I need 10x the time in qrss30 to do the qso with 100W,
> the needed energy is the same (compared to 1kW in qrss3). So, qsos could
> be done much faster if choosing 10x the power and stay in qrss3. The
> additional advantage would be, if I try to do a TA QSO I could just stay
> in the region of 137.7 and those who are qrv in qrss3 and only watch the
> qrss3-sector would get a nice signal and thus more fascination for the
> LF-hobby (I often think about the LWLs watching my transmission when no
> one is answering my call ;-)). In sum, the needed energy (=money) is the
> same but the needed time would be 10x less.
You are
right: the energy is the same. But spreading this energy over a longer
time has certain advantages:
- the more power you run the highter currents you will have (losses in
coils) and the higher antenna voltage (arcing, corona)
- a low power TX is cheaper and easier to build
- once you reach the legal 1W ERP limit "going slower" is the
only way to improve SNR. Either the simple way (QRSS at longer dotlength)
or the more sophisticated way (implementing error correction, cfr.
WSPR)


> What is the maximum power that
> is applied to an antenna yet? What have you heard yet? I have applied 1kW
> in a bad antenna (=> abt 100mW ERP), so 10kW would be possible when
> considering to stay in the legal limit. 10kW would be possible since one
> doesn't need a ferrite core that has to keep the power (in Class E mode).
> In USA it would be even more easy due to the fact that the 110V of
> the mains could just be rectified. Then I would take some
>
> STW12NK90Z in parallel and a
>
> IXDD414 and try it with 15A antenna current ;-)
It should
be possible to run a TX directly of the mains (giving about 330V DC). But
for 10kW the PSU current would be 33A, requiring something like a
60000uF/450V elco, these large HV elco's cost a fortune (at QRL we
recenty had to replace a 4700uF/450V capacitor, it costed  over 200
Euro).
And for a Class-D / Class-E amp running of 330V a 900V power FET might be
a bit on the edge for a foolprove TX (but since you are spending a
fortune on elco's you can spend some more money on 1.5kV devices ;-)
).

I hope I did not spoil the fun.

73, Rik  ON7YD - OR7T