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Message-ID: <3.0.1.16.20020102112100.2e074bee@pb623250.kuleuven.be>
Date: Wed, 02 Jan 2002 11:21:00
To: rsgb_lf_group@blacksheep.org
From: "Rik Strobbe" <rik.strobbe@fys.kuleuven.ac.be>
Subject: Re: LF: 136
In-reply-to: <3C2B6EFB.BCBFB23@ns.sympatico.ca>
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Hello Mal and John,

Assuming a QRSS QSO takes 2 hours you can have the same QSO in abt. 38
minutes using DFCW and in abt 22 minutes using 7FSK, leaving the SNR
unchanged.
Or the other way arround : if you want to make a 'standard QSO' within 2
hours you have to limit the dotlength to abt. 14 seconds, while you could
use abt. 43 seconds dotlength in DFCW and abt. 77 seconds dotlength in 7FSK.
This means that DFCW is abt. 5dB superior to QRSS while 7FSK is abt. 7.5dB
superior to QRSS and abt. 2.5dB superior to DFCW.
So John is right when he states that you win more by changing from QRSS to
DFCW than changing from DFCW to 7FSK (5dB vs. 2.5dB), but I would't ignore
this last 2.5dB.
To give an idea : 2.5dB is increasing the height of your antenna by 33% or
increasing the TX power by 78%.
Regarding bandwidth : at slow speeds (1 min. dotlength) even 7FSK fits well
within 1Hz.


73, Rik  ON7YD


At 13:57 27/12/01 -0500, you wrote:
>Hi Mal saw you last night also M0BMU
>      About QRSS, DFCW es 7 freq .  I find qrss to be very effective.  I
>believe DFCW is even more effective than QRSS because you can send info much
>faster for the same signal to noise ratio.  This makes sense because although
>it takes same time to send a dot but the dashes are 3 times faster.  It does
>take up more spectrum space than QRSS but the greater  efficiency will either
>get the info across faster during condx of QSB or the transmitter can go
>double the dot length and get the info across in the same time as QRSS for 3
>db improvement in received SNR.
>     The &FSK however takes up 3 times more spectrum space es I dont see any
>benefit in speed/SNR improvement
>     Jim your signals were received again through most of the night
>
>73 De John VE1ZJ
>gii3kev wrote:
>
>> john currie wrote:
>>
>> > Hi all Saw nil from OM2TW,  but will look more carefully later.  M0BMU
>> > was in all night with  the 7 freq format. Seems to take a lot of space
>> > .  Why will it be better?
>>
>> That is what I would also like to know. 7 fsk with tone spacing takes up
>> about 14 times more spectrum and is not compatable with others modes on
>> close adjacent frequencies, do not see any advantage with dfcw either
>> except that it and 7fsk are more noticeable on screen but that does not
>> constitute a better signal over noise transmission type or any advantage
>> over QRS which takes the minimum bandwith of all the modes to achieve the
>> object on a very narrow band.
>> A few nights ago someone was testing a data transmission around 135.920
>> khz taking up 500 hz of bandwidth, what is coming next !!!!!!!!!
>> While experiments with different modes are to be encouraged 136 khz is not
>> a suitable band with only 2 khz available, the only suitable mode for this
>> band is CW, normal speed and QRS.
>> Try the HF and VHF bands or Satellites where there is and abundance of
>> spectrum available for mode experimentation.
>>
>> > G3KEV
>> >
>> > Valerio,  OM2TW  will be gone on vacation for few days .  Perhaps you
>> > can transmit on 135.922 until he is back.  Best time seems to be from
>> > 0300 to your sunrise
>> >    Let me know if you will be transmitting es I will look for you.
>> > 73 all es hny de john VE1ZJ
>
>
>