The Butterfly filter doesn’t introduce phase shifts or impulse
response. It’s normalized for 170 Hz shift and for the most part,
the filter bandwith is set by the Universal M8000 firmware.
Every filter has differential phase shift and and group delay (impulse
response) characteristics.
Sometimes in the evenings I like to copy WLO broadcasting news and weather
using RTTY and SITOR mode B the frequency is 8.475.225 LSB. I decided to
use the K3's data mode and take advantage of the dual data filters.
I made this observation while using my Universal M-8000 Communications
Terminal
Here's are the actual Butterfly filter outputs using an Agilent DSOX3024
digital storage scope connected to the mark/space (or X/Y) outputs on the
M8000. The first image is the actual DSOX3024 screen shot with the K3 in
USB mode on 20 meters, copying RTTY 45/170. The second photo is the same
Here's are the actual Butterfly filter outputs using an Agilent DSOX3024
digital storage scope connected to the mark/space (or X/Y) outputs on the
M8000. The first image is the actual DSOX3024 screen shot with the K3 in
USB mode on 20 meters, copying RTTY 45/170. The second photo is the same
Looks like the FSK/DATA mode filter may be ringing - eyeballing the
filter envelope looks like it has some dips. A bit more bandwidth might
help - and the other time I've seen this is when there's a tuning error,
such that the two bandpass filters are not exactly centered on the
mark/space
The butterfly filters are tuned exactly to the tone frequency. When the
cross pattern is vertical, it's spot on 2125Hz, horizontal is exactly
2295Hz. I changed the DATA Mode to AFSK using a single filter and that
works the best. I found that the width control is optimized between 500 and
450
The next two photos shows the phase relationships as the tone transitions
from mark to space. The butterfly filter maintains a perfect out of phase
relationship using the AFSK, single filter, data mode. With the dual
filter, the phase relationship is sometimes in phase and then transistions
to
I found that the width control is optimized between 500 and 450 Hz.
Less than 450, the non-coherent phase shifts are introduced, as you
mentioned is caused by filter ringing.
What roofing filter are you using? If it is an Elecraft 5-pole filter
is the the offset properly set?
Are you using
My K3 defaults to FL3 which is the stock 2.7/5 filter. There is a 400 Hz
filter in FL2 but when it's selected, the phase distortion kicks in just a
little. You have to under the concept of the Butterfly filter. Both mark
and space filters are coherent filters and phase distortion in the
Nyquist in this context does not refer to the Nyquist criterion (i.e.
that the sample rate must be more than twice the highest signal
frequency). It just means a filter that has no inter-symbol
interference at a certain symbol rate (baud rate).
It turns out that if you start with completely
Alan Bloom wrote:
It might be possible to use separate Nyquist filters and detectors for
the two tones, treating each one as if it were a separate on/off-keyed
signal. If the transmitted signal is not filtered too heavily (i.e.
jumps quickly from one tone to the other) it seems like that
Al
Not at all, I'm sure you've helped more than just me! Thanks for the info.
73 Art
Alan Bloom wrote:
Nyquist in this context does not refer to the Nyquist criterion (i.e.
that the sample rate must be more than twice the highest signal
frequency). It just means a filter that has no
Using a excessively narrow filter on RTTY is a balancing act.
If the bandwidth is too narrow the tones tend to become smeared
- the transitions become less easy to detect (in other words,
the eye begins to close). However, narrowing the bandwidth
also reduces the amount of QRM/QRN making it
Re: using Nyquist filters for RTTY.
One complication I didn't mention is the fact that, because angle
modulation (FM, FSK, PM, PSK) is fundamentally non-linear, the
pre-detection and post-detection filters are fundamentally different.
With linear modulation types (AM, on-off keying, QPSK, QAM),
Alan Bloom wrote:
The problem is that different RTTY transmitters use different amounts of
filtering. However I suspect that a Nyquist receive filter designed
to compensate a typical/average transmit filter probably would have
pretty good performance on most received signals. Does anyone
Good point. It seems like an adaptive equalizer should work so long as
propagation hasn't totally garbaged the signal. However, it would
greatly increase the complexity of the demodulator. But maybe not if
the equalizer assumes a simple model of the transmit filter and makes
the a priori
I must be confused by this filter discussion. Is not a Nyquist filter by
its very definition a digital filter? Not directly comparable to the
crystal filters in the K3 or any other rig.
I would have supposed a Nyquist filter is one that samples at least
twice per cycle at the highest observed
To all you filter aficionados,
first of all thank you very much for all your detailed answers to my original
question, which roofing filter ist best for RTTY operation of the K3. Lots of
very detailed and informative answers were given and even a general discussion
on this issue among
I think it is just the difference between books and the real world. I
run AFSK, and with the K3 setup you can make full use of the filters.
If I want to drill into a signal the 400hz works well. You leave a
little drop off on each side. If you get it too narrow, the signal
does not decode
between these three roofing filters.
73,
Ed - W0YK
-Original Message-
From: [EMAIL PROTECTED] [mailto:elecraft-
[EMAIL PROTECTED] On Behalf Of Axel Kaiser
Sent: Sunday, May 18, 2008 5:15 AM
To: Elecraft Reflector
Subject: [Elecraft] RTTY filter for K3
To all you filter
To try and answer this question completely, I generated a single Spectrogram
plot showing:
1) A typical dual peak RTTY filter response (expect the K3 looks like
this). It was from a Timewave DSP-559ZX. Receiver IF filter is about 350Hz.
MTTY looks the same.
2) A RTTY signal.
I haven't
The RTTY decoder in fldigi is very good - I use this source in DM780.
Knowing how it works I am sure that a very tight 200Hz or 250Hz filter would
be fine. In fact it would be interesting to compare the K3's RTTY decoding
with external software, I'll do this sometime...
Simon Brown, HB9DRV
-
From: Axel Kaiser [EMAIL PROTECTED]
To: Elecraft Reflector elecraft@mailman.qth.net
Sent: Sunday, May 18, 2008 4:14 AM
Subject: [Elecraft] RTTY filter for K3
To all you filter aficionados,
first of all thank you very much for all your detailed answers to my
original question, which roofing
Order a 400 cycle filter and be done with it. You won't miss a contact.
Ken
http://www.cashcowhunter.com
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-PAN which should take care of that
little detail.
73
Steve Ellington
[EMAIL PROTECTED]
- Original Message -
From: Axel Kaiser [EMAIL PROTECTED]
To: Elecraft Reflector elecraft@mailman.qth.net
Sent: Sunday, May 18, 2008 4:14 AM
Subject: [Elecraft] RTTY filter for K3
At 01:14 AM 18 05 2008, Axel Kaiser, DL3ZH wrote:
This I can confirm also with my current OMNI VI+ which does not
allow me to copy RTTY signals with a 250 Hz filter .
Lieber Axel,
I use the 250 Hz all the time with my Omni VI+. Great performance:
good copy and little interference.
: K3KO [EMAIL PROTECTED]
To: elecraft@mailman.qth.net
Sent: Sunday, May 18, 2008 10:12 AM
Subject: Re: [Elecraft] RTTY filter for K3
Please turn on the K3 dual peak RTTY filter and tell us what you see then.
Brian/K3KO
n4lq wrote:
Axel
I was the first to respond to your question. I told you
You can change the MARK freq in AFSK A mode to one of four values
ranging from 915 Hz to 2125 Hz by pressing PITCH and rotating the VFO A
knob which, of course, will change the center frequency accordingly.
73,
Ken K3IU
n4lq wrote:
To use the DTF, I changed to
: Sunday, May 18, 2008 2:43 PM
Subject: Re: [Elecraft] RTTY filter for K3
You can change the MARK freq in AFSK A mode to one of four values
ranging from 915 Hz to 2125 Hz by pressing PITCH and rotating the VFO A
knob which, of course, will change the center frequency accordingly.
73,
Ken K3IU
: Ken K3IU [EMAIL PROTECTED]
To: n4lq [EMAIL PROTECTED]
Cc: elecraft@mailman.qth.net
Sent: Sunday, May 18, 2008 2:43 PM
Subject: Re: [Elecraft] RTTY filter for K3
You can change the MARK freq in AFSK A mode to one of four values
ranging from 915 Hz to 2125 Hz by pressing PITCH and rotating the VFO
@mailman.qth.net
Sent: Sunday, May 18, 2008 3:37 PM
Subject: Re: [Elecraft] RTTY filter for K3
As far as I know, the reason for having the capability of changing the
Mark freq is for personal preference in what you like to listen to. The
Dual PB filter works at whatever frequency you select. I can
Yes but it won't change the center fq. to 1500Hz so it will be like DATA
A. I'm not sure what the purpose of changing the pitch is.
DATA A is a general purpose mode. It is SSB with some features that
could cause distortion (like the speech processor) disabled. It is data
mode agnostic: you
, 2008 3:37 PM
Subject: Re: [Elecraft] RTTY filter for K3
As far as I know, the reason for having the capability of changing the
Mark freq is for personal preference in what you like to listen to. The
Dual PB filter works at whatever frequency you select. I can think of no
reason why AFSK
, May 18, 2008 5:04 PM
Subject: Re: [Elecraft] RTTY filter for K3
OK... thanks Steve. I am familiar with MixW... have used it for years
and I see what you are talking about. But let me suggest the
following... Go to AFSK A mode and set the mark frequency to 1445. That
will give you a center
...I
suggested to Lyle that they change the default center fq. in AFSK to
1500 so it will match Data A then let the user change as desired.
The center frequency in AFSK will be between the two tones selected for
the tone pair. It really can;t be anything else.
DATA A is a general purpose
, W4TV
-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of n4lq
Sent: Sunday, May 18, 2008 8:42 AM
To: Axel Kaiser; Elecraft Reflector
Subject: Re: [Elecraft] RTTY filter for K3
Axel
I was the first to respond to your question. I told you
On Sun, 2008-05-18 at 19:27, Joe Subich, W4TV wrote:
...
Using a excessively narrow filter on RTTY is a balancing act.
If the bandwidth is too narrow the tones tend to become smeared
- the transitions become less easy to detect (in other words,
the eye begins to close). However,
J. Edward (Ed) Muns wrote:
I agree with Joe's summary. Note that the 250 Hz 8-pole filter is
really about 370 Hz at the -6 dB point. Any of the current 500,
400 or 250 Hz crystal filters will be fine for RTTY. With any of
them, the DSP can be narrowed to 300 Hz without rolling off the
Hi Axel,
full ack with Joe. I use the 400 Hz 8 Pole with a DSP of about 300-350
in dual tone. Perfect!
73!
Frank, DD7ZT
Joe Subich, W4TV schrieb:
After making extensive tests and plotting the selectivity curves
of the 200 Hz filter in my K3, I'm convinced that it is too
narrow for
Frank Lammel wrote:
Joe Subich, W4TV schrieb:
After making extensive tests and plotting the selectivity curves of
the 200 Hz filter in my K3, I'm convinced that it is too narrow for
reliable weak signal RTTY operation, particularly in conjunction with
dual-tone filter.The measured
16, 2008 3:40 AM
Para: [EMAIL PROTECTED]
Cc: elecraft@mailman.qth.net
Assunto: Re: [Elecraft] RTTY Filter for K3
Hi Axel,
full ack with Joe. I use the 400 Hz 8 Pole with a DSP of about 300-350
in dual tone. Perfect!
73!
Frank, DD7ZT
Joe Subich, W4TV schrieb:
After making extensive tests
using the Mixw2
Best regards
Oms PY5EG
-Mensagem original-
De: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Em nome de Frank Lammel
Enviada em: Friday, May 16, 2008 3:40 AM
Para: [EMAIL PROTECTED]
Cc: elecraft@mailman.qth.net
Assunto: Re: [Elecraft] RTTY Filter for K3
Hi Axel,
full ack
: Friday, May 16, 2008 4:30 AM
To: elecraft@mailman.qth.net
Subject: Re: [Elecraft] RTTY Filter for K3
Frank Lammel wrote:
Joe Subich, W4TV schrieb:
After making extensive tests and plotting the selectivity
curves of
the 200 Hz filter in my K3, I'm convinced that it is too
narrow
One thing I don't see mentioned much - something that makes ALL the
difference in the world - is exactly *where* the bandwidth is measured on
the response curve.
Years ago I saw a lot of bandwidth measured at the -10 dB points (that was
probably before many K3 owners were born - I haven't seen
D'Eau Claire
Sent: Friday, May 16, 2008 7:40 PM
To: elecraft@mailman.qth.net
Subject: RE: [Elecraft] RTTY Filter for K3
One thing I don't see mentioned much - something that makes
ALL the difference in the world - is exactly *where* the
bandwidth is measured on the response curve.
Years
Subich, W4TV
Sent: Friday, May 16, 2008 12:28 AM
To: 'n4lq'; elecraft@mailman.qth.net
Subject: RE: [Elecraft] RTTY Filter for K3
I am watching RTTY right now and using the 200 Hz 5 pole
filter. The 170 HZ shift fits perfectly within the passband.
After making extensive tests and plotting
Hi K3-folks,
What would be the best RTTY roofing filter for the K3? Is the 400Hz 8-pole
filter too small and the 500Hz 5-pole filter the better choice?
Thanks in advance for your answers.
73 de
Axel, DL3ZH
_
Connect to the next
15, 2008 3:52 PM
Subject: [Elecraft] RTTY Filter for K3
Hi K3-folks,
What would be the best RTTY roofing filter for the K3? Is the 400Hz 8-pole
filter too small and the 500Hz 5-pole filter the better choice?
Thanks in advance for your answers.
73 de
Axel, DL3ZH
great!
73, John, W2GW
- Original Message -
From: Axel Kaiser [EMAIL PROTECTED]
To: Elecraft Reflector elecraft@mailman.qth.net
Sent: Thursday, May 15, 2008 3:52 PM
Subject: [Elecraft] RTTY Filter for K3
Hi K3-folks,
What would be the best RTTY roofing filter for the K3
Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of n4lq
Sent: Thursday, May 15, 2008 5:29 PM
To: Axel Kaiser; Elecraft Reflector
Subject: Re: [Elecraft] RTTY Filter for K3
Axel:
I am watching RTTY right now and using the 200 Hz 5 pole
filter. The 170 HZ
shift
On Mar 20, 2006, at 1:04 PM, k8rs wrote:
Now, I would like to know the
latest and best suggestions on the RTTY filter widths and which
frequency markers to insert on Spectrogram. Do you use two markers
170 Hz apart?
Depends on the software you are
I have enough BFO range as described in the manual and am able to reach
4912.97 on the low end. Unfortunately, while that is low enough for me
to center the RTTY filters on 1000Hz for one of the sidebands, it is not
for the other. On the bum sideband, the narrowest RTTY filters are
centered
Leigh,
Most if not all K2s will have a problem tuning for a 2200 Hz tone on both
sidebands, but 1000 Hz should be possible with some work on the BFO.
What you are asking to do is to have a BFO range of more than (IF center
frequency +/- 1000 Hz + filter width) - the center frequency is the real
Many thanks to Wolf - DL2WRJ for pointing out to me that I had not
aligned the reverse rtty filters, having done that
the problem is cured... Thanks Wolf !!! This list is a great resource.
73 de Tom K5VJZ
SN 4279
Lafayette, La.
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Elecraft mailing
Hi
Just did some playing with rtty and the K2.
I have a strange thing with the filter setup
I have set my filter for rtty in 1,5, 1, 0.5 and 0.25 kc. Using 1275/1440 tones.
I get the filter setting ok for all beside the 1 kc. When I use this filter I
notices a
jump of the center freq for about
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