[Elecraft] 700 Hz roofing filters

[Joe Subich, W4TV]

Jeff,

 > Because it's illegal.

The "roofing filter" does not set the transmitted bandwidth - that
is controlled in the DSP modulator.  The only purpose for roofing
filter in transmit is to remove the image of the IF and the FM filter
has more than sufficient skirt selectivity for that job (the image
is 30 KHz away).

 > > Thus, anything more than the 3KHz SSB bandwidth is against the
 > laws that govern us.

Incorrect in the USA.  There is no statutory maximum bandwidth though
my personal opinion is that anything more than 2.8KHz (200 Hz - 3000
Hz audio) is "bad practice."  Double sideband AM will require twice
the highest modulating frequency so 6 KHz is appropriate.  However,
again, it's the DSP that sets that bandwidth *not* the roofing filter.

73,

    ... Joe, W4TV


On 9/21/2010 8:19 PM, Jeff Cochrane - VK4BOF wrote:
> Hi Joe et al,
> I'm going to hazzard a guess here as to why Elecraft dont allow the 13KHz filter for AM/ESSB TX.
>
> Because it's illegal.
> SSB is called mode A3J in most of the legal documents that govern our hobby.
> The reason why the mode is called A3J in all the legal stuff is that the 3 is the maximum bandwidth in khz that is permitted.)
> Thus, anything more than the 3KHz SSB bandwidth is against the laws that govern us.
>
> The F.C.C. in the US of A and here in Australia, A.C.M.A. both allow a maximum of 3KHz for SSB TX bandwidth on any HF band.
> So it would be a fair bet then that because the K3 is a FCC type approved radio that part of that type approval includes that it must not transmit SSB bandwidths that are wider than permitted.
>
> My $0.02c worth (Plus GST/VAT/Sales Tax as applicable)
>
>
> Jeff Cochrane - VK4BOF
> Innisfail, QLD, Australia
> Elecraft K3# 4257
>
>    ----- Original Message -----
>    From: Joe Subich, W4TV
>    To: elecraft at mailman.qth.net
>    Sent: Wednesday, September 22, 2010 9:44 AM
>    Subject: Re: [Elecraft] 700 Hz roofing filters
>
>
>
>    In general I agree with Wayne although I prefer to have a more
>    narrow bandwidth option for SSB (1.8 or 1.5 KHz).  In order to
>    make room for the 1.5/1.8 KHz filter, I deleted the AM filter
>    and use only the FM filter for the "low priority" modes wider
>    than 2.8 KHz.  However, it continues to frustrate me that
>    Elecraft have *STILL* not allowed us to use the 13 KHz filter
>    for AM/ESSB transmit (officially).
>
>    In any case, given the measured performance of the INRAD/Elecraft
>    "250 Hz" filter (about 350 to 375 Hz), I can certainly see the
>    utility of something like:
>
>    FL1   13 kHz (FM/AM/ESSB)
>    FL2   2.7 or 2.8 kHz (SSB and casual CW/DATA tuning)
>    FL3   1.8 or 1.5 KHz (Narrow SSB and wide data modes)
>    FL4   700 Hz (casual/normal CW/DATA)
>    FL5   350 Hz (Narrow CW/RTTY in heavy QRM)
>
>    While the "350 Hz" filter would lack the absolute selectivity of
>    the Elecraft 200 Hz 5-pole filter, it would be nearly optimum
>    for 45.45 baud RTTY and still provide a useful "narrow CW" option.
>
>    73,
>
>        ... Joe, W4TV
>
>    On 9/21/2010 6:07 PM, Wayne Burdick wrote:
>    >  700 Hz is a useful CW/DATA filter bandwidth, certainly. I'm not
>    >  surprised that some K3 owners are interested in this.
>    >
>    >  Personally, I prefer much narrow CW/DATA bandwidths, and I use all
>    >  modes. The lineup I use (and generally recommend) is:
>    >
>    >  FL1   13 kHz (FM)
>    >  FL2   6 kHz (AM/ESSB)
>    >  FL3   2.7 or 2.8 kHz (SSB and casual CW/DATA tuning)
>    >  FL4   400 or 500 Hz (normal CW/DATA)
>    >  FL5   200 Hz (CW/DATA in heavy QRM)
>    >
>    >  73,
>    >  Wayne
>    >  N6KR
>    >
>    >
>    >  ______________________________________________________________
>    >  Elecraft mailing list
>    >  Home: http://mailman.qth.net/mailman/listinfo/elecraft
>    >  Help: http://mailman.qth.net/mmfaq.htm
>    >  Post: mailto:Elecraft at mailman.qth.net
>    >
>    >  This list hosted by: http://www.qsl.net
>    >  Please help support this email list: http://www.qsl.net/donate.html
>    >
>    ______________________________________________________________
>    Elecraft mailing list
>    Home: http://mailman.qth.net/mailman/listinfo/elecraft
>    Help: http://mailman.qth.net/mmfaq.htm
>    Post: mailto:Elecraft at mailman.qth.net
>
>    This list hosted by: http://www.qsl.net
>    Please help support this email list: http://www.qsl.net/donate.html
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>