[Elecraft] Field Day rig experience

Thu Jun 14 23:20:07 EDT 2018

Okay, I'll give up, we'll just have to agree to disagree.

On 6/14/2018 6:33 PM, WILLIE BABER wrote:
> Wes,
>
> "A "Roofing filter" is simply a filter in the radio's first IF through which all signals must pass before they will be "seen" by later receiver stages. The narrower this filter is, the less exposure later stages will have. Thus a "narrow" roofing filter is desirable -- but "narrow" is relative, as I'll explain."
>
> What Elecraft said (above) is exactly what I said.  Moreover, Elecraft's explanation is required because the term roofing filter is now applied to up-conversion in multiple conversion radios (with relatively wide first I-F filters compared to what is achievable at a low first I-F) which is what the term initially sought to rebuff in the first place, also my point.
>
> 73, Will, wj9b
>
> CWops #1085
> CWA Advisor levels II and III
> http://cwops.org/
>
> --------------------------------------------
> On Thu, 6/14/18, Wes Stewart <wes_n7ws at triconet.org> wrote:
>
>   Subject: Re: [Elecraft] Field Day rig experience
>   To: elecraft at mailman.qth.net
>   Date: Thursday, June 14, 2018, 4:47 PM
>   
>   Will,
>   
>   First of all I have said before and will repeat
>   it, I detest the term "roofing
>   filter."  That said, by the generally
>   accepted definition, you are wrong. See
>   Elecraft's take on this:
>   
>   http://www.elecraft.com/K3/Roofing_Filters.htm
>   
>   If you will think in
>   Wayne's terms, the post-mixer filter is a
>   "protective"
>   filter, not a
>   mode-specific filter.  So the question becomes, how much
>   
>   protection is necessary?  In
>   Elecraft's case, quite a lot, IMHO.  With its QRP
>   DNA, Elecraft uses post crystal filter
>   circuitry that minimizes current
>   consumption.  The trade off for this is the
>   need for a bank of pricey crystal
>   filters
>   to limit the frequencies that the circuitry is exposed
>   to.
>   
>   Now what if the
>   subsequent circuitry doesn't require this much
>   protection
>   because it is more robust?  We
>   now have direct-sampling radios that can digitize
>   a whole ham band with good performance. If the
>   BW was limited to 10-15 kHz in an
>   up
>   conversion configuration they should be even better.  The
>   limitation now
>   becomes LO phase noise, but
>   newer synthesizer designs overcome that obstacle.
>   Another thing to note is that IMD in crystal
>   filters is reported to be inversely
>   proportional to BW. So a wider filter might
>   actually be better from that
>   perspective.
>   Some Elecraft filters exhibit passive IMD BTW.
>   
>   Wes  N7WS
>   
>   On 6/14/2018 8:01 AM, WILLIE BABER wrote:
>   > Hello Wes,
>   >
>   > I took a look.  Both designs are using
>   the idea of "roofing filter" to refer to
>   up-conversion radios similar to the use of up-conversion
>   3khz filters as roofing filters in Icom radios.
>   >
>   > "Roofing
>   filter" (a mode specific filter after the first mixer
>   including narrow cw filters) only makes sense in the
>   context  of the history of superhet design and in
>   particular the use of one broad 15 khz first I-F (so that
>   all modes may pass through it) typical of all Japanese
>   radios until recently.  Calling a 45 mhz filter at the
>   first I-F a "roofing filter" as noted in the info
>   you sent entirely misses the point of what roofing filter
>   means.  Or, to put it another way, all Ten-Tec radios had
>   roofing filters in them (and were ssb and cw only) well
>   before the term roofing filter was coined!  Which is why an
>   Omni C will out perform any wide (15 khz) first I-F Japanese
>   radio, even those built well after the 1980 vintage Omni
>   C.
>   >
>   > Unless mode
>   specific up-conversion crystal filters can be made and as
>   narrow as 200 hz (this is possible with down-conversion)
>   then "roofing filter" and up conversion
>   doesn't make sense historically or in reality.
>   >
>   > Actually, Icom says
>   that did it with 1.2khz filter at 64 mhz in the Icom 7851,
>   though I'm not convinced the filter is that narrow, and
>   1.2khz is far from the 200hz filter that my K3 has in it
>   (however, the placement of this filter is why the 7851 is
>   among the best radios in Sherwood's chart, on cw).
>   >
>   > It is possible to
>   make very narrow and precise crystal filters as narrow as
>   the 200 hz inexpensively, and this is the point of having
>   multiple roofing filters at the first I-F.  So, this is the
>   origin of the term roofing filter---in comparison to the
>   barn-door up conversion first I-F.
>   >
>   > 73, Will, wj9b
>   >
>   > CWops #1085
>   > CWA
>   Advisor levels II and III
>   > http://cwops.org/
>   >
>   >
>   --------------------------------------------
>   > On Wed, 6/13/18, Wes Stewart<wes_n7ws at triconet.org>
>   wrote:
>   >
>   >   Subject:
>   Re: [Elecraft] Field Day rig experience
>   >   To:elecraft at mailman.qth.net
>   >   Date: Wednesday, June 13, 2018, 3:08
>   PM
>   >
>   >
>   Certainly not to disparage the
>   >   K3(S)
>   architecture (I have two of them) there is
>   >   nothing inherently wrong with an
>   up-conversion
>   >   receiver, if modern
>   hardware is used.
>   >
>   >   See:https://martein.home.xs4all.nl/pa3ake/hmode/g3sbi_intro.html
>   >
>   >   and my friend
>   Cornell's,
>   >   Star-10
>   transceiver.
>   >   https://pdfs.semanticscholar.org/eb33/5c12858779a653d9b9b93ca20120aebb7616.pdf
>   >
>   >   Wes  N7WS
>   >
>   >
>   >     On 6/13/2018 11:38 AM, WILLIE
>   BABER
>   >   wrote:
>   >
>   > Robert is talking about the
>   >
>   crystal filters, also known as roofing filters now-days,
>   >   that are typically placed after the
>   first mixer (I
>   >   mistakenly typed
>   "ahead" but I meant
>   >
>   "after" as Robert notes), though there is a
>   post
>   >   amp and NB before these filters
>   in K2 and K3.
>   >   >
>   >   > The idea is that a
>   >   crystal filter right after the first
>   mixer gives high
>   >   dynamic range
>   because high selectivity comes before the
>   >   receiver has developed stages of gain
>   that otherwise could
>   >   cause blocking
>   or IMD, especially when selectivity is
>   >   postponed to the second mixer while
>   ignoring gain
>   >   distribution in prior
>   stages of the receiver.  This basic
>   >
>   idea was popularized in Solid State Design for the Radio
>   >   Amateur, and it was applied to Ten-Tec
>   radios for decades
>   >   (at a 9 mhz
>   I-F).
>   >   >
>   >
>   >
>   >   Roofing filter gets defined in
>   relationship to Japanese
>   >   radios that
>   had up conversion 15 khz filters at the first
>   >   I-F, and generally lower dynamic range
>   as a result, (but you
>   >   got all modes,
>   general coverage, and optional crystal
>   >   filters at the second I-F).
>   >   >
>   >   > Good
>   for everyone radios.... but with
>   >
>   lower dynamic range and phase noise from the early
>   >   synthesizers.  This is why Ten-Tec
>   radios were so popular
>   >   among
>   contesters, especially Omni V and VI (modified with a
>   >   narrow cw filter at the first I-F).
>   >   >
>   >   > 73,
>   Will, wj9b
>   >   >
>   >
>   >
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