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Re: [RTTY] RTTY Filters: 250hz vs. 500hz

To: rtty@contesting.com
Subject: Re: [RTTY] RTTY Filters: 250hz vs. 500hz
From: Kai <k.siwiak@ieee.org>
Reply-to: k.siwiak@ieee.org
Date: Fri, 23 Aug 2013 14:59:53 -0400
List-post: <rtty@contesting.com">mailto:rtty@contesting.com>
Yes this is good practical advise. Remember also that whether you employ a 300, 500 Hz or even 2.8 kHz filter in the radio, the FINAL filtering is software-implemented in your RTTY demodulator software - and in some like MMTTY there is a dizzying array of software filter parameter choices. So, try to keep things linear till you get to that decoder. Play with RF-amp on or not, RF attenuation and AGC settings, that is, operate your radio, not just your automated logging program.
73
Kai, KE4PT

On 8/23/2013 2:48 PM, RLVZ@aol.com wrote:
Hi Guys,

After participating in dozens of RTTY contests and using  different radios,
my layman opinion is that "not all radios and crystal filters are created
equal".  Further, some hams are comfortable using real tight filters and
are not real concerned about decoding every  RTTY signal possible, whereas
other hams are more concerned about trying to copy every signal.  A couple  of
examples:

Difference in Radios/Filters: It seems like the  250hz filters on my old
FT-1000-MP were broader than the 250hz filter in my  K3.

Difference in Operators: Some great RTTY contesters have told me that
during RTTY  contests, they always run their K3 with 250hz roofing filter and a
DSP  setting of 350hz.  I've tried those exact filter settings on  dozens of
occassions on two different K3's whenever QRM gets  bad.  And I always go
back to a wider setting as soon as possible because  I'm unable to decode many
of the weaker signals whenever using the 250&  350hz filter settings.

Therefore, for the best possible reception, I believe  it's best to have
both a 250hz and a 400/500hz filter option and to be able to  switch between
them instantly, if possible.

Hope to work you in the SCC RTTY test this  weekend!

73,
Dick- K9OM




In a message dated 8/23/2013 11:45:02 A.M. Central Daylight Time,
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Today's Topics:

1. Re: 300hz or  500hz IF filter? (Jay WS7I)
2. S5xxEB stations in SCC RTTY  contest (Robert Bajuk)
3. Re: 300hz or 500hz IF filter?  (Kai)


----------------------------------------------------------------------

Message:  1
Date: Fri, 23 Aug 2013 08:19:50 -0700
From: Jay WS7I<ws7ik7tj@gmail.com>
To: rtty@contesting.com
Subject: Re: [RTTY]  300hz or 500hz IF filter?
Message-ID:<52177D96.6030502@gmail.com>
Content-Type: text/plain;  charset=ISO-8859-1; format=flowed

Joe-

You are just simply  wrong. And in any case the question was about
filters not the  signal.  Been using stacked 250 Hz filters for over 30
years on Icom,  Kenwood, Yaesu radio's.  They simply work in RTTY
contesting always  have and always will.  Theory, math, which I trust
Chen on far more  than I believe you may indicate something else but
experience tells me  narrow is better for contesting,  perhaps wider for
weak signals but  if they are that weak most won't hear them at all
during a contest which  is why DXing if different from Contesting.


On 8/23/2013 8:05 AM,  Joe Subich, W4TV wrote:
And most FSK signals are 370 Hz wide or  more


------------------------------

Message: 2
Date:  Fri, 23 Aug 2013 17:47:40 +0200
From: Robert Bajuk<rbajuk@gmail.com>
To: rtty@contesting.com
Subject: [RTTY] S5xxEB  stations in SCC RTTY contest
Message-ID:
<CACzNusnqoVRG21Aqow4BGJee_Z3Y0NT-zPvKT2AGx+kH8R+ZTg@mail.gmail.com>
Content-Type:  text/plain; charset=ISO-8859-1

Special callsigns S5xxEB have been  issued in order to promote the
greatest sporting
event in Slovenia this  year - EuroBasket 2013 (4. - 22. September 2013).

See more about the  event on the official webpage:
http://www.eurobasket2013.org

S5xxEB  stations active in SCC RTTY contest will sign RST + *2013* for  this
purpose.

73 Robert, S57AW
SCC Contest  Manager


------------------------------

Message: 3
Date:  Fri, 23 Aug 2013 11:58:54 -0400
From: Kai<k.siwiak@ieee.org>
To:  rtty@contesting.com
Subject: Re: [RTTY] 300hz or 500hz IF  filter?
Message-ID:<521786BE.2080503@ieee.org>
Content-Type:  text/plain; charset=ISO-8859-1; format=flowed

The RTTY elements are  either 22 ms (bits and start bit) or between 22 and
44 ms
(1 to 2 stop bit  lengths), usually 33 ms (1.5 bit lengths)..
I've never heard of a half bit  length tone (11 ms) sent in isolation.

That means the spectrum will be  dominated by the 1000/22 = 45.45 Hz
component,
and will have a fine  underlying structure of 1000/33= 30.3 Hz component.
99% of
the energy is  contained withing 250 Hz.

I agree with the K3 comment - that is one  cool radio.

-Kai KE4PT

On 8/23/2013 11:05 AM, Joe Subich, W4TV  wrote:
No, the half bit makes the baud rate effectively 90.9  (the shortest
element is now 11 ms) thus the calculation  is:
     (2 * 90.9) + (1.2 * 170) = 385.5 Hz.
  although the actual occupied bandwidth will be dependent on the
  information content (how often/how regularly transitions occur will
  effect the value of "K" in the previous formula).

  Alternatively, observe RTTY signals on-air.
And most FSK  signals are 370 Hz wide or more depending on the care
with which the  manufacturer has designed the FSK circuits.  The only
exception  are later versions of the K3 firmware which generate very
clean FSK  using DSP.

73,

    ... Joe,  W4TV


On 8/23/2013 8:15 AM, Kai wrote:
  Absolutely incorrect. Consult ITU-R SM.1138:  BW = 2M + 2DK;  D=shift/2;
M = Baud/2   K = 1.2 (typically)
  BWrtty=2M+2DK = Baud + shift*1.2 =249.5 Hz

If you  consider the effect of the 33 ms (1.5 bit) stop bit, that effect
  has a narrower spectrum which is contained entirely within the 249.5  Hz
BW of the 22 ms start and Baudot bits. The shortest element is  still 22
ms.
Alternatively, observe RTTY signals  on-air.

Kai,  KE4PT




On 8/22/2013  10:34 PM, Joe Subich, W4TV wrote:
On 8/22/2013  9:42 PM, Kai wrote:
The theoretical bandwidth of 170 Hz  shift 45.45 baud RTTY is just
under 250  Hz.
Absolutely incorrect as 250 Hz does not  account for the necessary
modulation sidebands or for the  discontinuity (additional bandwidth)
generated by the 1.5 bit  stop.  Due of the half bit, the necessary
bandwidth for  170 Hz shift RTTY approaches 170 + (2 * 90.9 * 1.2) or
  slightly over 370 Hz as the shortest element is now 11  ms.

73,

   ... Joe, W4TV


On  8/22/2013 9:42 PM, Kai wrote:
The theoretical bandwidth of  170 Hz shift 45.45 baud RTTY is just
under
250  Hz.
73
Kai,  KE4PT

On 8/22/2013 6:54 PM, Joe  Subich, W4TV wrote:
The -6 dB  bandwidth of the INRAD "300 Hz" filter is shown as 340  Hz
which is slightly less than the theoretical 370 Hz  required for 170
Hz
shift 45.45 baud  RTTY.

That said, performance  will be a trade off between improved
selectivity and  interference rejection - up to a point.  If the
  receiver can withstand AGC effects of close in interference, a  400
to 500 Hz filter will generally provide better  copy than a 300 Hz
filter.  Note: no amount of  selectivity is useful when signals
overlap or the  interfering signal includes distortion (spurious)
  products that overlap the desired  signal.

  73,

    ... Joe,  W4TV


  On 8/22/2013 5:38 PM, David VE3VID wrote:
Hello  everyoneI would like to outfit my FT-857D portable rig with
an
IF filter on its 455khz stage.  INRAD  sells a suitable 500hz unit.
They also have a  300hz unit.   I am leery about the 300hz  filter
being too  narrow.
Any opinions?
  73Davidhttp://www.ve3vid.webs.com/
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End  of RTTY Digest, Vol 128, Issue  23
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