Anyone know what the bandwidth of a 50 baud RTTY signal might be?

garyr wrote:
Anyone know what the bandwidth of a 50 baud RTTY signal might be?

It depends on the shift, but at the 170 Hz standard it is about 300 Hz
and the amateur standard 45.45 baud at 170 hz is about 250 Hz.


--
Jim Pennino

Remove .spam.sux to reply.

The bandwidth will depend on what shift is being used. Some of the more
common shifts are 170,425, and 850 Hz.

The actual bandwidth needed to receive them will be slightly larger.
Something like 200 for the 170 Hz shift and 1200 for the 850 Hz shift. The
transmitted bandwidth will be larger yet.

It is similar to an FM signal, it theory it is infinite,but in practice it
can be much less.



"garyr" wrote in message
...
Anyone know what the bandwidth of a 50 baud RTTY signal might be?

"Ralph Mowery" ha scritto nel messaggio
m...
The bandwidth will depend on what shift is being used. Some of the more
common shifts are 170,425, and 850 Hz.

The actual bandwidth needed to receive them will be slightly larger.
Something like 200 for the 170 Hz shift and 1200 for the 850 Hz shift.
The transmitted bandwidth will be larger yet.

It is similar to an FM signal, it theory it is infinite,but in practice it
can be much less.



"garyr" wrote in message
...
Anyone know what the bandwidth of a 50 baud RTTY signal might be?




Consider also the group delay of receiving filter...
with narrow Butterworth or Chebyshev crystal filters, group delay is big,
distorting
RTTY , CW or other digital signals, and ultimate result is error in
decoding.

So bandwidth need to be more than necessary. A Gaussian filter is better for
group delay,
but is worse for steepness.

73, Piero.

On Sat, 12 Mar 2011, Piero Soldi wrote:

"Ralph Mowery" ha scritto nel messaggio
m...
The bandwidth will depend on what shift is being used. Some of the more
common shifts are 170,425, and 850 Hz.

The actual bandwidth needed to receive them will be slightly larger.
Something like 200 for the 170 Hz shift and 1200 for the 850 Hz shift.
The transmitted bandwidth will be larger yet.

It is similar to an FM signal, it theory it is infinite,but in practice it
can be much less.



"garyr" wrote in message
...
Anyone know what the bandwidth of a 50 baud RTTY signal might be?




Consider also the group delay of receiving filter...
with narrow Butterworth or Chebyshev crystal filters, group delay is big,
distorting
RTTY , CW or other digital signals, and ultimate result is error in
decoding.

So bandwidth need to be more than necessary. A Gaussian filter is better for
group delay,
but is worse for steepness.


I figured the original question was the bandwidth the signal took, rather
than the bandwidth of the receiver.

I didn't think anyone went for a receiver filter to match the RTTY signal.
Well maybe the hardcore RTTYers. But generally one used a reasonable
filter in the receiver, and counted on the audio filters in the
demodulator. There again, relative few decoded at the IF, but even then
the articles I've seen didn't go for any special narrow filters for RTTY.

Michael VE2BVW

Thanks for all your replies. I should have explained the reason for my
question. I've become interested in SID (Sudden Ionosphere Disturbance)
monitoring: http://www.aavso.org/solar-sids
This basically involves monitoring the signal strength of various VLF
stations that transmit a 50-baud RTTY signal. Knowing nothing about the
spectrum of these signals I build a receiver that has a bandwidth of about
200 Hz and it works reasonably well on one station that transmits on 21.4
KHz. I would like to use it to also monitor a signal on 25.2 KHz.
However, I happen to live about 50 miles from a 500 KW station
that transmits on 24.8 KHz and that signal swamps everything within 600 to
800 Hz. So I thought a narrow bandwidth might be better and was about to
start construction of one when I learned the nature of the transmissions so
I thought I had better get some information on the actual bandwidths
involved. Hence my query.

I would appreciate your comments regarding the design of my VLF rig: The
antenna is a shielded, tuned loop www.febo.com/time-frerq/wwvb/antenna. The
receiver is a direct-conversion type. I use a FST3125 quad FET bus switch as
a mixer with the LO derived from a DDS source. The mixer output is amplified
(60 dB) and fed to a 5-pole 120 Hz Butterworth LP which also provides about
27 dB of gain. The filter output is rectified and integrated (5.4 sec TC)
and is the input to the ADC on a microprocessor (on a separate board) that
collects and stores the data for later download to a PC. The construction is
a mixture of through-hole and surface-mount parts on a two-sided PC board.
Is it possible that I have a shielding problem when tuned near the nearby
station? Is it likely that I would have better results if my receiver was in
a shielded enclosure?

Thanks in advance for your coments and advice.
Gary Richardson, AA7VM


"garyr" wrote in message
...
Anyone know what the bandwidth of a 50 baud RTTY signal might be?

Il 12/03/2011 18.25, Michael Black ha scritto:
On Sat, 12 Mar 2011, Piero Soldi wrote:

"Ralph Mowery" ha scritto nel messaggio
m...
The bandwidth will depend on what shift is being used. Some of the more
common shifts are 170,425, and 850 Hz.

The actual bandwidth needed to receive them will be slightly larger.
Something like 200 for the 170 Hz shift and 1200 for the 850 Hz shift.
The transmitted bandwidth will be larger yet.

It is similar to an FM signal, it theory it is infinite,but in
practice it
can be much less.



"garyr" wrote in message
...
Anyone know what the bandwidth of a 50 baud RTTY signal might be?




Consider also the group delay of receiving filter...
with narrow Butterworth or Chebyshev crystal filters, group delay is big,
distorting
RTTY , CW or other digital signals, and ultimate result is error in
decoding.

So bandwidth need to be more than necessary. A Gaussian filter is
better for
group delay,
but is worse for steepness.


I figured the original question was the bandwidth the signal took,
rather than the bandwidth of the receiver.

I didn't think anyone went for a receiver filter to match the RTTY signal.
Well maybe the hardcore RTTYers. But generally one used a reasonable
filter in the receiver, and counted on the audio filters in the
demodulator. There again, relative few decoded at the IF, but even then
the articles I've seen didn't go for any special narrow filters for RTTY.

Michael VE2BVW

Hi Michael,
i was an hardcore RTTYer a lot of years ago... :-)

I've used Teletype Corp ( now IBM ) TG7, Kleinschmidt TT100,
Olivetti T2, Siemens ??? and after, first attempts of software
decoders.

Yes, normally you use a CW filter to receive RTTY, ie: 500/600 Hz BW for
170 Hz shift so the group delay is not problematic if rf tones are
centered in passband of filter ( stay away from edges ).

Cheers,
Piero I5SPO