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[TowerTalk] Matching 75 ohm hardline for 3 bands

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Subject: [TowerTalk] Matching 75 ohm hardline for 3 bands
From: (Michael Foerster)
Date: Sun, 1 Apr 2001 11:59:56 -0500

I think that you're right.

I must have read the table wrong, showing that I would have 6db of loss.
After reading your mail, and rethinking this, adding the hard-line and the
mismatch losses or Un-Un losses, it would probably be greater than the 9913
that I'm using.

Thanks a lot, and thanks to everyone else for the suggestions.  I did learn
a great deal.


----- Original Message -----
From: "Roger D. Johnson" <>
To: "Michael Foerster" <>
Sent: Saturday, March 31, 2001 1:51 PM
Subject: Re: [TowerTalk] Matching 75 ohm hardline for 3 bands

> Hi Mike...
> It seems the thread has gotten off to tri-band HF antennas! I
> looked up the loss figures in the ARRL Handbook and 9913 has
> 3db/100 ft at 450MHz. The figures they give for 75 ohm "hard-
> line" (it doesn't say air or foam) are 2.3 db for 1/2 in and
> 1.7 db for 3/4 in. Then there is the problem of connectors.
> Most folks cobble up their own out of plumbing fittings. What
> is the loss thru these at 450MHz? What about jumper cables at
> each end? Since each band will hardly be 50 ohms non-reactive
> at all frequencies, there may be impedances that produce greater
> than 1.5-1 SWR at certain bands/frequencies resulting in more
> loss. Matching transformers at each end might be OK for HF but
> I doubt they will be bebeficial at UHF. Also, the VHF/UHF bands
> are not harmonically related so the HF method of making the line
> a 1/2 wavelength long at the lowest freq will not work.
>  My opinion is to stick with the 9913 unless you can afford to
> replace it with lower loss 50 ohm cable. Another approach might
> be to buy a higher gain antenna to offset the losses.
> 73 and GL, Roger

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