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,
rtty-request@contesting.com writes:
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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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