On 2/17/2013 5:54 PM, Bob McGraw - K4TAX wrote:
I'll take an air-wound inductor over a toroidal inductor any day,
space available. The typical loss in an air-wound inductor is IR loss
where a toroidal has IR loss plus eddy current loss.
That may be too broad a generalization. While I haven't crunched the
numbers for specific designs, I recently completed VNWA measurements of
all the bandpass filter boxes I could get my hands on for
multi-transmitter HF stations. Some use air-wound inductors, some do
not. The filters having the lowest loss and the best performance are the
W3NQN designs, both those sold by Array Solutions buit by W3NQN, and
those implemented by Bob, 5B4AGN, in his TXBPF kits. Those designs use
two different mixes of powdered iron cores for the lower bands, and
non-magnetic toroidal cores (essentially a PVC coil form) for 15 and
10M. The W3NQN designs also vary the wire size from one band to another.
My report, which includes photos of the filter sets and lots of measured
data, is at
http://http://audiosystemsgroup.com/BandpassFilterSurvey.pdf
73, Jim K9YC
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