Re: LF: Link budget calculation or estimation of dist for given power on WSPR

[Andy Talbot <andy.g4jnt@googlemail.com>]

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

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2010/1/10 Roger Lapthorn <rogerlapthorn@gmail.com>

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 <g3kevmal@talktalk.net>

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.

 

G3KEV

 

----- Original Message -----

From: Roger Lapthorn

To: rsgb_lf_group@blacksheep.org

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 <james.cowburn@virgin.net>

 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 james.cowburn@virgin.net

 

 

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G3XBM    GQRP 1678      ISWL G11088

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http://g3xbm-qrp.blogspot.com/
http://www.g3xbm.co.uk
http://www.youtube.com/user/G3XBM
G3XBM    GQRP 1678      ISWL G11088