Hi Brian, Thanks for your comprehensive post on the implementation of my Pre-filter. I have inserted my comments between yours.
73 Stewart G3RXQ On Thu, 17 Mar 2005 09:50:24 -0800, Brian Broggie wrote: > We are getting a lot of requests for the parts to make G3RXQ's K2 Pre > > Filter. To facilitate this, we have made a build list with all the > parts that we can supply for a nominal charge. The list is based on the > description and schematic found on G3RXQ's website. Included are the > crystals, caps, toroids, magnet wire, a pc board and an 8 pin > connector. The total cost for the parts is $29.00, plus shipping (and > CA tax to orders inside California). Please order by part "K2PREFILTER". > > While we encourage hams like you to explore and try new circuits and > ideas with our products, please be aware that any modifications to our > products come at a tradeoff to the original design. Here are some > guidelines from the owners of Elecraft and designers of the K2, Wayne > Burdick and Eric Swartz... > > 1. Overall receiver gain and noise figure may degrade because the added > crystal filter will have some loss of around 5 dB. >> >> If the Pre-filter is used in place of the noise blanker I have observed >> negligible additional signal path loss. >> As I said in my article one of the benefits of this mod is that it can >> be easily installed or removed. You then have the choice to listen to weak >> signals on a quiet band (with the noise blanker removing pulse interference) >> or with the Pre-filter in to work weak signals next to S9+40dB contest >> stations. > > 2. K2s with older crystals in their RF board and KSB2 filters may not > have the exact same center frequency as the ones we're using (and > shipping) now. The effect would be that the new filter would overlap the > old, reducing the effective bandwidth on receive. The only way to ensure > that this doesn't happen on older K2s would be to replace all 14 > crystals (RF board and KSB2). A new set of 14 matched crystals can be > ordered from Elecraft as part "K2KSB2XTLS". >> >> Yes, it is very important that new crystals should not be put in front of a >> KSB2 filter that contains old ones. Anyway, it is a good time to upgrade >> your crystals to get the best performance from your KSB2. >> > > 3. The crystal filter does not have the pad in front of it. The Pad > normally is either part of the KNB2 or the PCB if no KNB2 is installed. > (The pad gives the 2N5109 amp stage before it a good return loss match.) > It will degrade K2 IMD Dynamic range by over 10 dB (IMDDR3 and IP3) > without this pad. Reinstalling the PCB pad will not help as it would end > up between the two SSB xtal filters. > >> This may be true. I have no test equipment that is up to the task of >> measuring the K2 IMD (which is already very good). >> In a recent contest I noticed that the benefits of the Pre-filter >> outweighed the slight loss of IMD dynamic range. > 4. Finally, you should be aware that the KDSP2 does the same thing for > ultimate rejection, since the regular filter more than filters enough to > keep off freq signals from pumping the K2s AGC, allowing the DSP to > clean up any residual blow-by. > >> I'm not so sure about about this statement. The KDSP2 processes audio after >> the AGC loop, so although the received signals may sound cleaner it has no >> effect that I can see on AGC pumping caused by either a lack of filter shape >>factor or blow-by. >> > Thanks, Wayne and Eric! >> Seconded - nice to get feedback... > > So, evaluate the data on G3RXQ's website and what we are presenting in > this email and order accordingly. > > 73, > Brian Broggie - W6FVI > Elecraft Parts > _______________________________________________ > Elecraft mailing list > Post to: Elecraft@mailman.qth.net > You must be a subscriber to post to the list. > Subscriber Info (Addr. Change, sub, unsub etc.): > http://mailman.qth.net/mailman/listinfo/elecraft > > Help: http://mailman.qth.net/subscribers.htm > Elecraft web page: http://www.elecraft.com _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
