The Mysterious K3 Roofing Filter Scheme

[alorona]

Hi, Everybody,
 
Sorry to ask questions that have probably been asked thousands of times before, but the Elecraft archives have no good way of searching by keywords.
 
I know very little of the K3, and nothing has been more difficult to get my head around than the filter arrangement. Consider a K3 with KRX3.
 
I think I've determined that a K3 cannot use filters installed in the KRX3, nor can the KRX3 use filters that are in the K3's slots. Furthermore, I think I've determined that for diversity receiving there should be identical filters in each receiver. I think I've determined that these identical filters do not have to be in corresponding slots, as long as they're there somewhere.
 
I think I've determined that the widest filter goes closest to FL1. I think I've determined that empty slots are okay. I think I've determined that 8-pole filters have zero offset, but 5-pole filters do have an offset.
 
I think I've determined that any filter which will be used for transmitting must go in the K3 (and not the KRX3).
 
If all of this is correct, then please read on. If not, please correct me.
 
Here's what I haven't determined yet: under what conditions it is necessary to match (2) 5-pole filters. Is it when I have a 5-pole in the K3 and a 5-pole in the KRX3, of identical bandwidth? or different bandwidths? Probably identical, based on my understanding of diversity reception above. But maybe not.
 
Here's something else that I haven't determined: why do I keep seeing references to 'variable-bandwidth' filters, but absolutely no information about what they are or where they come from?
 
Has there ever been a ham who experienced as much difficulty deciphering all of this as me? Why not? What do you young whipper-snappers eat for breakfast?
 
What the world needs is a good tutorial on the K3 crystal filter scheme. I don't wish my present quandary on anybody.
 
Thanks very much.
 
Good weekend,
 
Al  W6LX
 
 
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[Bill W4ZV]

Al Lorona wrote

Here's something else that I haven't determined: why do I keep seeing references to 'variable-bandwidth' filters, but absolutely no information about what they are or where they come from?

The variable BW roofing filters were a *future* described at the original K3 introduction.  They have not yet been introduced.  Read about them and more below:

http://www.zerobeat.net/mediawiki/index.php/K3_Roofing_Filters

Your assumptions on the other issues are all correct.

73,  Bill