Owen Duffy wrote in
:

....
So for small diameter 50 ohm polyethylene dielectric line at 1.8MHz,
the worst case for most ham applications, Xo/Ro is about .18. For
that, I used 2.7dB/100ft for RG174 type line. That's getting to be

I make the loss/100' of RG174 to be 1.1dB and from that I get Xo=-3.6
ohms. (Did you get loss/100m from somewhere? This is probably the
answer to Cecil's diligent spot of an apparent error.)


Tom, in view of your comment about skin effect not being well developed
in RG174, I went to Belden's data sheet for 8216 (RG174 type) and sure
enough, the loss below 30 MHZ does not track the loss=k1*f^0.5+k2*f
model. Your loss figure of 2.7dB/100' may well be correct, and my line
loss calculator is in error below 30MHz for this particular cable due to
the thin copper plating and steel core of the inner conductor. TLDETAILS
and other calculators based on the same loss model will also be in error.
I note that the ARRL TLW shows 1.8dB/100' for 8216 at 1.8MHz.

This sets me thinking of a way to calculate a lower frequency limit to
the loss model when I generate it, so that I can store that limit in the
database and prevent calculation below that frequency.

Owen