We are obviously mainly engineers here!. A
question was asked, and has been responded too in some considerable depth and
detail and diverging opinions proffered. The questioner now knows a
little more than he did at the start, but without an explicit answer to the
question asked, other than “it depends”!
Of course if we were consultants we would
tell people what they already knew after asking them first and then charge them
for it!
Thanks for all the replies, and It looks
like I am going to need “considerably bigger buns”!
Thanks Andy and all
interested in the group for the information.
Surely there is nothing
like a practical experiment for proof of WSPR effectiveness against QRSS3 on
500KHz. I have been running that experiment since the 17th of
November 2009.
Results so far have been,
hundreds of WSPR reports from 7different stations and not one mention of the
QRSS3 content.
My MEPT runs a 100%
Transmit cycle, hence once I got a reliably detectable signal out I posted this
to the UK500KHz Group on the 28th of November 2009. :-
“Between the WSPR is QRSS Morse and some small
font Hell which looks best
on Spectran QRSS3 Mode. This means it's a continuous TX sequence. I
think at the bottom of the WSPR Window and with such low power it should
not cause any problems to any other stations. Please let me know if
there are any concerns.”
I have run MEPT’s on
continuous transmit tests at the bottom the WSPR slot on other low occupancy
bands without any problems too. I always use QRPp. After all who is going to
complain about the QRSS3 etc. content of the signal that has never been seen?
As I have mentioned before,
there has to be a challenge in there somewhere for the guys with big antennas.
There is a simple 2 letter ident in there in 2 QRSS3 modes as well as more
complex stuff and full Call Sign..
-----Original Message-----
From: owner-[email protected]
[mailto:owner-[email protected]]
On Behalf Of Andy Talbot
Sent: 10 January 2010 21:20
To: [email protected]
Subject: Re: LF: Link budget
calculation or estimation of dist for given power on WSPR
Making
comparisons between WSPR and QRSS should take into account the signalling rate,
and it is only fair to compare like with like.
A WSPR
transmission carries a callsign, a locator and a power level.
Approximately 12 characters worth of data, or in Morse
code terms around 2.4 words which it sends in 2 minutes - hence about
1.2 WPM. If 12WPM beans 100ms dots, then this rate corresponds to a
dot interval of 1 second. So for a fair comparison, you must
compare WSPR with 1s QRS - which I believe is faster than most ops actually
use. The version of Argo I have only goes down to 3s dots which
infers 5dB bandwidth improvement immediately.
So if, as I
recall someone saying here, WSPR and 3s QRSS give similar decoding capability,
then that immediately suggests WSPR is 5dB 'up' on QRSS, or QRSS takes
three times longer for the same message.
Its rather
more complicated in reality, as this simple ccomparison assumes the QRS
signal is copied with zero errors. As it involves fuzzy logic and human
interpretation, we can probably say it contributes the error correction
To compare
data modes in noise, its best to use a normalised data rate expressed in
Bits/second/Hz
See http://www.g4jnt.com/MartleSham.htm where
I come up with an empirically determined estimate that the WSJT modes, WSPR,
JT4, etc give about 6dB enhancement in S/N vs. decoding than CW - when
normalised for an equivalent signalling rate.
Andy
www.g4jnt.com
This email has been scanned for damaging side-effects by the health and safety
police, is guaranteed to contain no substances hazardous to health, but may
contribute to dissolving the nether and polar regions
2010/1/10
Roger Lapthorn <[email protected]>
Fair comment Mal, and one of these days
I'll try QRS and see how it performs.
It should be possible to get a pretty good idea of the theoretical range limit
for WSPR on 500kHz based on required S/N (which can be as low as -30dB for
WSPR), path loss calculations, ERP etc.. I shall be interested to see what
"the experts" say.
73s
Roger G3XBM
2010/1/10 mal hamilton <[email protected]>
Had u been on QRS CW he
probably would have copied u since he saw ur
trace. I often see traces that do not decode for some time but had the trace
been keyed it could have been identified.
I have been making this
point for some time, avoid guesswork and speculation and use normal CW or
QRS CW
Regardless of erp
transmitted the weakness is often at the RX end Little antenna Little signal
Big antenna Big signal and environment regarding noise.
RX loop antennas not
optimised towards ur
stn, these situations cannot be calculated just guessed and meaningless.
Get into QSO mode and see
how far u can get in real time.
----- Original Message
-----
Sent:
Sunday, January 10, 2010 7:02 PM
Subject:
Re: LF: Link budget calculation or estimation of dist for given power on WSPR
Certainly GM4SLV has a much lower noise
floor than most stations on 500kHz Jim. I think he estimated about 10dB lower,
so it may be easier for him to hear very weak signals than many others.
For what it's worth, my 1mW ERP has been received at -18dB S/N at 990kms range
in S.Germany (and at around -23dB a few times), so assuming another 10-12dB in
hand, that must be good for another skywave "hop" under favourable
conditions. I am still hopeful that TF3HZ might just spot me on a good night.
The magic 1000kms barrier is tantalisingly close. RN3AGC says he might just
have seen a "whisper" of a trace from me the other night and he is
2400kms away, but if it was me it was far too weak to decode.
It will be interesting to see what people say is possible based on the
propagation theory etc.
73s
Roger G3XBM
2010/1/10
James Cowburn <[email protected]>
Dear LF,
Has anyone any ideas or
suggestions on a resource for calculation of a link budget for WSPR over a set
distance?
As it seems I can get up
to GM4SLV reasonably consistently on my current antenna/power setting with a
SNR of around -22dB and the limit for WSPR is around -30dB then is there a
means for roughly estimating or indeed accurately calculating the Expected Max
Range (EMR) at that power setting and antenna configuration?
Clearly, there are
differences between separate Rx stations but if one knows the ratio between two
or more Rx stations then it should be possible to pro-rate or estimate at least
the signal strength at a given Rx based on its performance with other known
signals.
If I can do 916km with an
SNR of say -22dB then how much further would the remaining 8dB or so of
WSPR detection get me, assuming the other Rx has the same capability as GM4SLV
and if their capability is different, then is it fine to factor for the dB
difference over known paths/signals?
Thanks in advance for any
answers or pointers and best wishes to all for a great 2010
With
best regards
Jim
Dr.
James Cowburn G7NKS
E
[email protected]
--
http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/G3XBM
G3XBM GQRP 1678 ISWL G11088
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