While all the 'lawyers' have been discussing contest rules, I have been
thinking about contest equipment; so, here is something for the
'technical types'....
At the risk of being flamed about the subject relevance to contesting, I
am seeking knowledge about the resurgence of Collins mechanical IF
filters in new HF rigs (for CONTESTing, of course). With the imminent
changes in the ham licensing regulations, coupled with the increasing
band activities due to Sun spot number growth, I am on a quest to
possibly improve the adjacent signal handling capabilities of my trusty
TS850 and backup TS830.
Please consider the following:
The Yaesu FT-1000MP includes a Collins filter in the 455 KHz IF. When I
first inquired as to why they used a mechanical filter versus a crystal
filter, I was informed (don't remember who) that it was more for the
nostalgic aspect related to Yaesu's founder JA1MP, in which the Collins
filter was the latest technology back then.
The recent QST review of the Yaesu FT-847 noted the availability of an
optional Collins IF mechanical filter.
A review of the latest AES catalog (Summer 98) for Yaesu equipment and
options noted Collins filters available for the FT1000/D, FT920, and
FRG100B receiver.
A look at the Signal One web page (www.bbcyber.com/signalone/) for their
MILSPEC 1030CI transceiver (modified Icom IC781) noted the use of two
Collins 2.1 kHz filters cascaded at the 455 kHz IF.
AOR's (www.aorja.com) "High Performance DDS HF Receiver", model AR3030,
uses the Collins mechanical filters. They state "in contrast to ceramic
filters, Collins mechanical filters are more expensive and rarely used in
any but the very top of the range and professional equipment". This
statement was obviously written by someone in marketing and not
engineering.
Now the questions:
Why are these filters better than the more popular standard
stock/optional crystal filters? Are they better than the INRAD (formerly
IRCI) filters? What kind of insertion loss is associated with the
mechanical filters versus the 5-8 dB for INRAD crystal filters? Is there
a good book/article that discusses this subject?
Please respond directly to me.
73,
Henry Pollock - K4TMC
Raleigh, NC
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