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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