[UK-CONTEST] RTTY Bandwidth

[G4LMW]

David

Wow!, thanks for the in-depth response (which I had to read several times to 
absorb!)

I appreciate that there are many factors that affect bandwidth of any 
transmission. Also, with a good notch filter in the centre of my 400Hz 
passband, I can resolve overlapping signals fairly easily

However, my point was that with everything else being equal, 75 baud will 
occupy greater bandwidth than 45.45 baud.

Rob

----- Original Message ----- 
From: "David G3YYD" <g3yyd at btinternet.com>
To: <UK-Contest at contesting.com>
Sent: Monday, July 25, 2011 5:19 PM
Subject: [UK-CONTEST] RTTY Bandwidth


> Rob
>
> RTTY occupied bandwidth is like CW bandwidth depends how hard the keying
> is and how strong the signal is. With little to no filtering then the
> bandwidth will be measured in KHz for a strong signal. A strong signal
> with good TX filtering will occupy about 400Hz of bandwidth. Then it
> depends how good the RX filtering and performance is. In high activity
> RTTY contests I normally use RX bandwidth of 250Hz at -6dB with around
> 350Hz at -60dB.
>
> With a +/-200Hz TX signal bandwidth and a RX +/- 150Hz (about -30dB down
> side of filter then PC software filtering. I can copy the next signal
> QRM free at about 350Hz spacing between signal centre frequencies.
> Before you think I have got my maths wrong remember it is TX to RX that
> counts and not TX to TX adjacent TX clicks can overlap. Of course if you
> are using a FT897 with SSB filters you will have a problem, both in
> filtering and dynamic range of the RX.
>
> Some TX signals are a lot wider and therefore 350Hz spacing is not
> possible for all TX/RX pairings. Penalty points for transmitting wide
> signals would be an excellent idea and with SDR technology easy to
> provide proof. With today's very stable rigs and software RTTY could
> amend rules to a narrower shift, 85Hz?, has to be used. Or could go to
> Minimum Shift Keying (MSK) at baud rate/2, i.e just under 23Hz. Reducing
> the shift to 85Hz would reduce occupied bandwidth and adjacent channel
> spacing comes down by 85Hz.
>
> Incidentally the minimum occupied bandwidth for a RTTY FSK signal can be
> very small compared to current practice.  Minimum shift of baud rate/2
> Hz coupled with optimum TX filtering gives occupied bandwidth of shift
> plus baud rate in Hz. For 45.45 baud this is  22.73+45.45=68.2Hz say
> 70Hz. Allow a bit extra for signal spacing could have 10 run frequencies
> per KHz instead of less than 3 for the current practice. 75 Baud would
> occupy 102.5Hz with a bit extra say 8 per 10KHz.
>
> Of course it will never happen as it is always easier to preserve the
> status quo. In the "RadCom Letter" subject heading on the reflector much
> has been written about contesters pushing the technology envelope so may
> be that is what we should do. We want (need?) more run frequencies per
> KHz so why not change the RTTY shift to a much smaller one? Given the
> nature of contesting, it would have to be a rule rather than just a few
> changing to their contest disadvantage.
>
> 73 David G3YYD
>
> On 25/07/2011 14:14, G4LMW wrote:
>> It is worth mentioning that the main reason that PSK was introduced was 
>> to
>> help alleviate the overcrowding that was experienced with the RTTY ONLY
>> contests.
>>
>> Also, should there be a move to 75 baud, then each signal will occupy 
>> 370Hz
>> instead of 270Hz (happy to be corrected on my exact numbers).
>>
>> So, RTTY ONLY with 75 baud would be worse that ever!
>>
>> Regards
>> Rob, G4LMW
>>
>> ----- Original Message -----
>> From: "john reynolds"<g3rsd at btinternet.com>
>> To:<uk-contest at contesting.com>
>> Sent: Monday, July 25, 2011 2:57 PM
>> Subject: [UK-CONTEST] UK Contest data modes in CC
>>
>>
>>> I believe CC was intended to encourage and train operators in all modes 
>>> of
>>> on air communications used in contesting.
>>>
>>> Before the CC's I had never used Ry or PSK.
>>>
>>> Probably because of my age,it took me a long time to configure and use
>>> Data Modes and it was thanks to other local Amateurs that I am now
>>> comfortable with all modes.
>>>
>>> I do not think DATA should be dropped from these Contests, but it could 
>>> be
>>> modified!!
>>>
>>> May I suggest that on alternate Months RTTY only is used and it be left 
>>> to
>>> the individual to use whatever speed they wish to achieve maximum 
>>> points.
>>>
>>> The following Month PSK would be the mode and here again speed is left 
>>> to
>>> the individual.
>>>
>>> May I also point out that a close "Observer" who has suffered Contesting
>>> for Years considers that the "SHOUTING" mode should be dropped 
>>> ...........
>>> it is most unsociable  around the house!!
>>>
>>> John (JR)  G3RSD
>>> _______________________________________________
>>> UK-Contest mailing list
>>> UK-Contest at contesting.com
>>> http://lists.contesting.com/mailman/listinfo/uk-contest
>>>
>>
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