[Elecraft] Auto Bandpass Filter

[Dick Dievendorff]

If you are doing this for an SO2R or multi-transmitter installation and no
two radios never ever need to be on the same band, perhaps you can configure
the switching to use one set of separately enclosed W3NQN filters rather
than a pair of products that has a switch and six filters each.

There's a fair amount of connector cost and jumper jungle associated with a
solution like this, which needs to be compared with the cost of the W3NQN
bandpass filters themselves.  A set of six distinct W3NQN filters and a pair
of 2 x n switches is a bit more flexible (and might provide a bit better
isolation) than a box containing a switch and six filters. But it's messy
and takes up a lot of space. 

I considered this option, and chose two boxes containing switches and 6
filters instead.  I didn't like the jumper jungle.  There is a (perhaps
small) market for a 2 x 6 SO2R bandpass filter box with four coax
connectors, radio 1 in and out, radio 2 in and out.

There used to be a note on the Array Solutions site that described this
configuration, associated with their FM-6.  The product offering was two
FM-6's, a set of six W3NQN filters and a lot of jumpers. I can't find it
now. Perhaps it has been superseded by the much "neater" configuration with
a separate set of filters for each radio.

One multi-op I visit uses just one set of six separately enclosed W3NQN
filters, connected to the input side of each of six single-band amplifiers.
Amp/bandpass filter selection is performed by routing a radio to one of the
amplifiers.  Antenna switching consists of selecting one of the available
antennas for that band only.

Still another multi-radio single operator configuration I saw some years ago
used separate radios and amps (that shared a common HV supply) and antenna
tuners for each band.  The single operator changed bands by rolling his
chair to a new position.

Dick, K6KR