Yeah, I just did that with a large reel of RG6. I just stripped the
cable back so about 1/4" of center conductor was exposed. I pushed the
exposed center conductor into type-F jack of the adapter on my MFJ-269
far enough that part of the annular ring of the shield touched the outer
conductor of the type-F jack. I was a little surprised, but this was
good enough to get frequency readings for two adjacent impedance minimums.
Short clip leads work pretty well, too. Somewhere I have a couple of
PL-259s that have clip leads attached to the back side for that sort of
thing.
73, Mike W4EF.......................
On 1/12/2020 11:14 AM, jimlux wrote:
On 1/12/20 10:24 AM, David Gilbert wrote:
If you have an antenna analyzer that can measure complex impedance
(as in R +/- jX) and if you are willing to put a connector on one end
of the cable, I can tell you how to get an accurate length
measurement using TLW, the transmission line application that comes
free with the ARRL Antenna Book. You don't need an instrument with
TDR capability (Time Delay Reflectometer) to do it.
73,
I'll bet you could do it without a connector and using clipleads. it's
probably around 200 ft long (60 or so meters, maybe 80 meters
electrical length, depending on the velocity factor)
So a few inches or feet won't make much of a difference.
You tune the antenna analyzer until you get a peak in SWR - that will
be a multiple of a quarter wavelength. If it's an odd multiple of 1/4
wavelength, the open at the far end is transformed to a short at the
SWR meter end. If it's a even multiple of a 1/4 wavelength (multiple
of 1/2 wavelength), the open at the far end shows up as an open at the
meter end. Both are "infinite SWR".
if you sweep around 1.8 MHz and you get that peak, that's probably the
1/2 wavelength scenario. and so forth.
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