[Elecraft] Field Day rig experience

[WILLIE BABER]

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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