Other strong signals in the passband of the IF will densense the
following stages and cause AGC action. If you have no AGC, then you
will overdrive the sound card audio stage with the strong signal in an
attempt to copy the wreak one.
The DSP filter in ICOM rigs is at the IF level and is accomplishing the
same effect as an xtal or mechanical filter in some other rig such as an
FT-817, because it is before the AGC.
73,
Leigh/WA5ZNU
On Wed, 7 Mar 2007 12:43 pm, Danny Douglas 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: <digitalradio@yahoogroups.com>
> 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
>> >
>> >
>>
>>
>>
>>
>>
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> 9:24 AM
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