Yes I agree Stefan.
I just wanted a clear answer from someone like Andy regarding the theoretical difference between WSPR (with it's strong error correction) and QRSS at various speeds. In the limit very slow QRSS is bound to win but WSPR allows a lot of data to be fed back to the TX station immediately after just a 110sec burst.
Still to try ROS!
73s Roger G3XBM
Via my iPod Touch 4g 2.4GHz handheld.
Hello Roger,
OK about WSPR beeing about equal to QRSS-3 in sensitivity.
But if you just want to test how far you can get with your signal, why
don't you try QRSS-60? This must have an improvement of > 10 dB and
there are plenty of grabbers running arround your QTH. G4WGT, F1AFJ,
DK7FC, DF6NM, OE3GHB.... We all are monitoring the band sectors all the
time. Everybody can read the signals, meaningless if QRSS or DFCW or
slow hell... You can even have an offset of say 2 Hz or a drift of say
1 Hz/hour. The grabbers are running anyway, so you don't even have to
ask for listening stations if you want to do tests...
Isn't that even simpler and ideal for such tests?
73, Stefan/DK7FC
Am 24.08.2011 20:56, schrieb Roger Lapthorn:
Hi Marcelino
Thanks for this.
Yes I understand fully what is needed for LF/MF WSPR and have
implemented simple and low cost WSPR solutions using transverters for
both 136 and 500kHz with some excellent results on the latter band -
see my website
for details. On 136kHz WSPR my best DX is 148km with a VERY low ERP and
simple antenna.
This autumn I am improving the ERP on both bands and hope to better my
DX on WSPR considerably. I also confidently predict that the system
improvements will allow me to have my first CW QSO with G3KEV and
others on 136kHz. I have already worked him on 500kHz CW with 1mW ERP
thanks to his good ears and good system and antennas.
73s
Roger G3XBM
On 24 August 2011 19:36, Marcelino Garcia <[email protected]>
wrote:
Roger,
I fully agree with your statements, but I'm
afraid that with a minimalist home made CW transmitter, let's say just
a one transistor xtal oscillator, it's not possible to use WSPR, for
this mode a little more complex transmitter, may be SDR based, should
be used.
73,
Marcelino - LU7DSU
De:
Roger Lapthorn <[email protected]>
Para: [email protected]
Enviado: miércoles,
24 de agosto de 2011 15:18
Asunto: Re: LF: WSPR
or QRSS: which is better?
Mal
Thanks again for your comments, some of which are valid.
There are times when CW is useful and times when more efficient modes
like WSPR really win out.
As I have said countless times now, no other mode apart from WSPR that
I know of is able to give me almost instant feedback (via the internet
database) at a distance that (a) my signal is being received at all,
(b) how far it is getting, and (c) how strong it is. To be able to get
this information when using simple, low powered and home made equipment
is extremely useful. A small change in the PA output or antenna
efficiency is measurable.
It really comes down to what is the purpose of our experiments: being
able to make CW contacts is a perfectly reasonable aim - please carry
on. In my case it is to see just what is possible with minimalist
(hardware) equipment on the VLF, LF and MF bands. Yes, I am gaining
valuable dBs by the use of efficient coding systems and clever PC
software, but I see nothing wrong in that.
And finally, please do NOT call me an appliance operator: all my VLF-MF
equipment is home-made as is much of my HF and VHF gear. I am happy to
use modern technology to enhance my enjoyment of the hobby and to
exploit weak signal modes but I am equally happy to have a CW QSO on
any band when the opportunity arises.
73s
Roger G3XBM
On 24 August 2011 18:48, mal hamilton <[email protected]>
wrote:
Jim take NOTE
Impulsive noise generates a random output
that looks like a valid callsign so this is also inventing a signal
that you imagine to exist.
An immediate positive ID, don't depend on
it !!
An appliance communications operator is
easily hoodwinked.
Bletchley Park CW expert Radio Operators
managed to piece messages together and achieved the object., and no
doubt used imagination.
No expertise is need to send/receive wspr
and for that matter a lot of other appliance operator modes, know in
the services today as IDIOT PROOF comms black boxes.
For a commercial operator that needs to
shift thousands of messages worldwide then automated digital modes are
necessary and useful, but for a radio hobbyist its like using a sledge
hammer to crack the proverbial nut
g3kev
Original Message -----
Sent:
Wednesday, August 24, 2011 6:06 PM
Subject:
Re: LF: WSPR or QRSS: which is better?
I know what you're referring to. In cases of impulsive
noise, there is a finite probability of something eventually getting
through the decoder and being flagged as valid. The very nature of
heavy source coding, means that the resulting random output will look
like a valid callsign. However, WE then apply the next level of error
detection, by knowing the combination must be rubbish.
'jnt [and there is another example of source coding]
On 24 August 2011 17:47, Graham <[email protected]>
wrote:
>> and gives absolutely guaranteed error free
decoding, or nothing at all. <<
Are you sure ?
G..
Sent: Wednesday, August 24, 2011 5:12 PM
Subject: Re: LF: WSPR or QRSS: which is better?
WSPR works in a 1.46Hz signal bandwidth and because of
its very high level of error correction and soft-decision decoding,
means that it will work at a S/N of about 3dB in this bandwidth, and
sometimes a bit lower still (Normally, FSK with no correction at
all needs about 10 - 12dB S/N for near error-free performance)
QRSS has to show about 6 - 10dB in its signal bandwidth
to be able to discern fully what is sent, although a slightly lower S/N
may be useable when you 'know' what you should be receiving. (A form
of forward error correction is now in use here as well perhaps :-) So
lets say 5dB S/N is a working value..
So take 3dB in 1.46Hz as a starting point and derive the
bandwidth for QRSS needed to get 5dB S/N with the same signal. This
will have to be narrower to get a 2dB higher S/N and works out as
1.46 / 10^(2/10) = 0.92Hz
So QRSS used with a 0.9Hz bandwidth - which I think
means about a 2 - 3s dot period ought to be decoded at the same S/N as
a WSPR signal. Which is probably the info you wanted.
But now compare source coding efficiencies. WSPR fits
a callsign, locator and power level into a 110 second transmission -
and gives absolutely guaranteed error free decoding, or nothing at
all. About 12 characters in actuality, but that is being a bit unfair
as the coding forces certain callsign and locator formatting. So in
all probablility, more like 7 or 8 effective characters (I'm being a
bit empirical here)
Assuming standard QRSS - not DFCW - , which if like
standard Morse, then 5 characters takes about 50 dot symbols to send
(12WPM = 60 chars in 1 minute, = 1 char / second, or about 10 dot
periods / second. Dot speed = WPM / 1.2) If we have 2s dots, that
is 5 characters can be sent in the time for a WSPR transmission.
So as a quick estimate, WSPR wins by roughly 2dB in S/N
terms for a given dot period / noise bandwidth. And at similar S/N
values, WSPR is about 1.5 times faster
Andy
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbm
https://sites.google.com/site/sub9khz/
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