What I was saying your second paragraph. A string signal darkens the
waterfall and suppresses weak signals. IF filtering eliminates this.
If the signal is a few KHz away and [uficiently strong that IF filtering
doesn't then that is the close-in performance of your rig, but that is a
different issue. DSP at the AF doesn't help this, unless it is your
soundcard that is overloaded, which is less likely as that usually shows
up as distortion ("harmonics" of the signal that go away if you reduce
gain).
Leigh/WA5ZNU
On Wed, 7 Mar 2007 2:14 pm, Andrew O'Brien wrote:
> I agee with Danny and don't quite "get" what Leigh is saying.
>
> Dave's question is an interesting one because with my 3-week old DSP
> capable rig I, have been experimenting with the issue Dave raised. I
> have the ability to go down to 50 Hz IF-DSP filtering , but to be
> honest I find the digital bands to be so sparsely populated that I have
> not needed to use th filtering tha much. I'm waiting for a big contest
> to test this further.
>
> With regard to what Leigh is saying, I have been anxious to find out if
> my variable AGC and/or DSP filtering offer any significant improvement
> over the infamous "strong PSK signal 'desenses' other signals in
> waterfall" issue. With my admittedly little playing around, I have not
> found the AGC settings to make that much difference. I just noticed a
> strong PSK31 signal way out at the 1700 Hz mark on my waterfall. When
> he transmits my Multipsk waterfall darkens considerably. Turning a
> fitter on , in this case 1000Hz, eliminates the strong signal at 1700
> and the waterfall at the lower end returns to normal. I still have
> not figured out how to best "center" on the remaining waterfall with
> software commands to center on 1000 or 1500 Hz, since these commands
> center you to parts of the band that you may have filtered out. Still
> need to find time to practice more. I guess I need filter o! ut the
> strong signals, shift the remainder of the waterfall so that it is
> centered on 1000 Hz an then use "align" or "center" macros. Sounds
> like work though.
>
> Dave, I think 500 Hz should be all you need for all but the most
> unusual situations.
>
> On 3/7/07, Danny Douglas <[EMAIL PROTECTED]> wrote:
>
>> I have a hard time visualizing the need for a narrow filter, for such
>> narrow
>>
>> modes. You can sit, in PSK for instance, slap up against another PSK
>> signal
>> and still copy much weaker signals. Thats the whole purpose of the
>> narrow
>> band digital modes to start with. I use WinWarbler (now) to do my
>> digital
>> transmission in both PSK and RTTY, and when I want to do something like
>> Olivia or MFSK etc. I go to MixW. I particularly like WinWarbler
>> because it
>> has the wide band copy ability in PSK. I.E it will automatically copy
>> (and
>> show all the channels) in a 2 or 3 KC bandwidth - at the same time.
>> Using a
>> narrow filter in there would completely negate that fantistic
>> capability.
>>
>> I have never had to use my narrow filters in order to copy a digital
>> signal, and yes I have played with them to see what difference it made.
>> Todays rigs, with their dsp filtering just seem to bypass any need at
>> all
>> for additional filters for digital operation, though I do see the need
>> for
>> CW filters, and have 250 and 270 cy fliters in my two rigs because I
>> use my
>> ears, and not the computer to detect and read that mode.
>>
>> Danny Douglas N7DC
>> ex WN5QMX ET2US WA5UKR ET3USA
>> SV0WPP VS6DD N7DC/YV5 G5CTB all
>> DX 2-6 years each
>> .
>> QSL LOTW-buro- direct
>> As courtesy I upload to eQSL but if you
>> use that - also pls upload to LOTW
>> or hard card.
>>
>> moderator [EMAIL PROTECTED]
>> moderator http://groups.yahoo.com/group/DXandTalk and RTTY,
>>
>> Danny Douglas N7DC
>> ex WN5QMX ET2US WA5UKR ET3USA
>> SV0WPP VS6DD N7DC/YV5 G5CTB all
>> DX 2-6 years each
>> .
>> QSL LOTW-buro- direct
>> As courtesy I upload to eQSL but if you
>> use that - also pls upload to LOTW
>> or hard card.
>>
>> moderator [EMAIL PROTECTED]
>> moderator http://groups.yahoo.com/group/DXandTalkK vfor i
>> Danny Douglas N7DC
>> ex WN5QMX ET2US WA5UKR ET3USA
>> SV0WPP VS6DD N7DC/YV5 G5CTB all
>> DX 2-6 years each
>> .
>> QSL LOTW-buro- direct
>> As courtesy I upload to eQSL but if you
>> use that - also pls upload to LOTW
>> or hard card.
>>
>> moderator [EMAIL PROTECTED]
>> moderator http://groups.yahoo.com/group/DXandTalk
>>
>> ----- Original Message -----
>> From: "kv9u" <[EMAIL PROTECTED] >
>> To: <[email protected]>
>> Sent: Wednesday, March 07, 2007 2:24 PM
>> Subject: Re: [digitalradio] narrow filters/PSK
>>
>>> Hi Dave,
>>>
>>> Yes, the narrower filters will help a great deal. I have an ICOM rig
>>> that needs to be centered on 1500 Hz when operating in SSB modes so I
>>> try and move them to that point if I can. Then I have DSP filters that
>>> enable me to close the "window" as tight as I need to. I also have
>>> Twin
>>> PBT which enables me to dial each side of the interference. But the
>>> actual bandpass filters are much more effective with the really strong
>>> signals.
>>>
>>> If I could only have one additional filter than the stock SSB
>>> filter, I
>>> would go for the 500 Hz filter since it is very useful for CW use as
>>> well as narrow to medium digital modes. I have a 270 Hz crystal filter
>>> in my Kenwood TS-440SAT that I find rather narrow although some might
>>> prefer that for CW.
>>>
>>> If you go narrower than 500 Hz, you can not use a number of digital
>>> modes that are around or slightly under 500 Hz, but may not fit well
>>> into at 250 Hz bandpass.
>>>
>>> 73,
>>>
>>> Rick, KV9U
>>>
>>> Dave wrote:
>>> > Has anyone tried using either a 250 Hz or 500 Hz filter for PSK31
>>> > reception? My Icom IC-746 (non-Pro) has no filters installed, and is
>>> > wide as a barn door on USB for PSK31. I wondered if either of these
>>> > filters would help, or would they be too narrow?
>>> >
>>> > The pass-band shift does a fair job of eliminating QRM from one side
>>> > or the other of the selected frequency, but when there are two very
>>> > strong signals within 2 Khz on each side at the same time, they just
>>> > aren't effective on both.
>>> >
>>> > Any input appreciated!
>>> >
>>> > Thanks in advance es 73
>>> > Dave
>>> > KB3MOW
>>> >
>>> >
>>>
>>>
>>>
>>>
>>>
>>
>>> Announce your digital presence via our DX Cluster
>> telnet://cluster.dynalias.org
>>>
>>> Our other groups:
>>>
>>> http://groups.yahoo.com/group/dxlist/
>>> http://groups.yahoo.com/group/themixwgroup
>>> http://groups.yahoo.com/group/contesting
>>> http://groups.yahoo.com/group/wnyar
>>> http://groups.yahoo.com/group/Omnibus97
>>>
>>>
>>> Yahoo! Groups Links
>>>
>>>
>>>
>>>
>>>
>>> --
>>> No virus found in this incoming message.
>>> Checked by AVG Free Edition.
>>> Version: 7.5.446 / Virus Database: 268.18.7/713 - Release Date:
>>> 3/7/2007
>> 9:24 AM
>>>
>>>
>
> --
>
> Andy K3UK
> Skype Me : callto://andyobrien73
> www.obriensweb.com
