Question:
Would it not be easier to just have two extra wires cut for for the low
end and the other for the high end of each band and feed them from a
common feed point with minimal matching components such as series fixed
capacitors to bring each wire to resonance? This perhaps could broaden
the response but may not be a perfect match depending on how far the
wires were separated from each other. It may be a suitable way to avoid
buying a lot of expensive components.
Herb Schoenbohm, KV4FZ
On 9/14/2014 7:01 PM, Jim Lux wrote:
On 9/14/14, 3:36 PM, TexasRF--- via TowerTalk wrote:
Conceptually this could be done using 50 ohm coax stub matching.
Starting with the R +j of the four band segments, a design for each band
series segment can be done. Then starting with the shortest series
section,
additional series cables can be added to achieve the proper length
for the
remaining three band segments. The junctions of the four series coax
sections can be connected with Tee connectors. Then four shunt stubs
could be
connected by means of suitable relay on the third leg of the Tee
connectors.
I have not done this for the stated application but have used the
concept
to switch a 40m beam from cw to phone frequencies with excellent
results. In
this case, only two stubs were switched in/out.
When doing the design, there are multiple solutions with stub matching.
Some solutions require a shorted stub, others require an open stub.
One can
visit the various solutions and choose one that minimizes the amount
of coax
needed.
As usual, I am only the concept guy; you have to do the work.
Transmission
line software will make the job easier.
Or lumped LCs.. in general, with N lumped LCs you can get a perfect
match at N frequencies.
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