[Elecraft] 700 Hz roofing filters [Thread REALLY closed]

Wed Sep 22 00:10:34 EDT 2010

Guys - this thread has been formally closed. (both the 700 hz and ESSB sub threads).

Please take further discussion off list.

73,
Eric
Elecraft List Moderator - really!

www.elecraft.com
_..._

On Sep 21, 2010, at 6:43 PM, "Joe Subich, W4TV" <lists at subich.com> wrote:

> 
> 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
>>> 
>>> 
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