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RE: 7x7 UHF Arrow antenna for portable AO40



Hello Wayne

> Now it's time to build the power splitter/matching
> cables.  I ordered an all-female BNC Tee and four
> 75-ohm BNC connectors from RadioShack.com.  I have
> some 75-ohm RG-59 cable.  Now I need to figure out
> the exact length of the coax needed to make the ¼
> wavelength matching cables.  I know the velocity
> factor of the coax (82%), but I don't know the
> "length" and velocity factor of a BNC plug/jack.

IMHO RG-59 VF is 67%. See www.g6lvb.com/rg59splitter.jpg for a pic of my
splitter made from the same bits as yours. I can't tell you exactly what
lengths I cut the braid, inner etc, as I never took any notes. You can work
it out from the pic though and your individual BNC plug measurements. I get
1.0:1 with this splitter measured on an MFJ 269 at 433MHz and two yagi's
also measuring 1.0:1 at this frequency. A miracle. Kind of one of those
things that just worked one day. It had to happen one day, just like the law
of monkeys and typewriters. Similar VSWR's were measured on SWR meters too.

> Is the velocity factor 100% for BNC plug, BNC jack, and BNC Tee?

As for BNC's - I just sort of guessed at 67%, as it's solid dielectric all
the way through. This would add up to 11.5cm total, but as you can see the
length is actually 12.5cm from BNC end to the center of the T piece. That
takes into account the fact that nearly 1cm into the left hand BNC it should
present 50 ohms to the antenna feed point BNC. That was the theory.

One final thing - use good quality T pieces, not thin ethernet tatt at
435MHz. I've wasted many hours on that one.

Hope that helps...

73 Howard G6LVB

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