Ok Roger, Thank you! I will take a deep look into your website, I just read about your 137 khz transverter and found it a very interesting project. I would like to have enough time to start building some equipment for LF, I'm just starting with reception on 137 khz band, we don't have yet the 500 khz band here in Argentina, hope we could get it soon. 73, Marcelino - LU7DSU
De: Roger Lapthorn <[email protected]>
Para: [email protected]
Enviado: miércoles, 24 de agosto de 2011 15:56
Asunto: Re: LF: WSPR or QRSS: which is better?
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/g3xbmhttps://sites.google.com/site/sub9khz/
-- http://g3xbm-qrp.blogspot.com/http://www.g3xbm.co.uk
http://www.youtube.com/user/g3xbmhttps://sites.google.com/site/sub9khz/
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