[TowerTalk] Cable TV hardline question

[MIKE GREENWAY]

There was a good article on using non-synchoronous transformers versus stub
matching on 75 ohm cable TV hardline, and how to build them in the Sept 1978
Ham Radio magazine.  I have used a non-synchronous transformer on both ends
of a 200 ft run of scrap cable TV hardline for my 40 M beam for over 20
years and it works well.  I used the W2FMI 50/75 torroid transformers that
Amidon and other sells on my multi band antennas since the non-synchronous
is for one band only.  73 Mike K4PI

----- Original Message ----- 
From: "Tom Rauch" <w8ji at contesting.com>
To: "Tim Holmes" <W8TAH at Zoominternet.net>; <TowerTalk at contesting.com>
Sent: Friday, October 29, 2004 1:59 PM
Subject: Re: [TowerTalk] Cable TV hardline question


> > I also came up with some Cable TV hardline.  Its 1/2 inch
> (I think) -
> > Jacketed in PVC with an Air Dialectric.  I have been
> looking for ways to
> > connect it for my VHF / UHF antennas.  Also I am concerned
> about the
> > impedence mismatch.
>
> I would be concerned also, since the cable can cause an SWR
> of over 2:1 at the radio.
> Most VHF and UHF radios do not tolerate such a high SWR this
> very well.
>
> What you can do is build a transformer using lengths of 50
> and 75 ohm cable mixed. It is pretty tricky to do this at
> UHF, but it can be done if you have the test gear and are
> careful. I don't have references, but I'd bet someone else
> does. The devices are called non-synchronous transformers.
>
> I certainly look into matching the cable at VHF or UHF, not
> because of cable loss but because of bandwidth and impedance
> problems at the radio. A 2:1 SWR is not good for most
> radios.
>
> 73 Tom
>
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>
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>
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