I have continued my search for good connectors for my CATV coax. As I
mentioned in my previous post, the first step is to figure out exactly
what kind of coax you have. I found most of mine on the Commscope website
(www.commscope.com) and I have the QR type coax in various sizes.
When I got the coax, I did also score a few pin type connectors for the
coax. At first, I had no idea that these were actually useful. Normally,
the pin goes inside some kind of equipment like an amplifier. However,
you can screw the outer housing of a N connector onto the threads and by
cutting the pin at the right length (and deburring it), you end up with
a male N connector (thanks K2UA for this hint). You can use whatever
adapters you need at that point.
These pin connectors can be found pretty cheap.
At www.tmbrokersmontana.com I found the ones I needed listed and the prices
very reasonable (depending on the size, from $3.50 to $6 each).
They also had some splices for my larger hardline for just under $10 that
will allow me to put together some shorter pieces to make a nice long
one. You can find instructions on how to prepare the cable on the
manufacturer's web site in most cases.
Even if you can't find these surplus, I found other places that had them
new for not too much more money.
Also - remember that e-bay is a great place to find your coring tools to
prepare the coax. Expect to pay $20 to $35 for them.
Not happy about using 75 Ohm coax in your feedline? You can construct a
simple transformer to change 75 Ohms to 50 Ohms.
The JULY-AUGUST 1981 issue of the NCJ shows how to make one.
Cut 0.08165 wavelength lengths of 50 Ohm coax and 75 Ohm coax (mind your
velocity factors!!). Splice them together and connect the 75 Ohm end to
your 50 Ohm load/tranmitter and connect the 50 Ohm end to your hardline.
The NCJ shows the following lengths for Regular RG8/11 or foam RG8/11:
regular (.66VF) foam (.79VF)
80M 14' 8" 17' 7"
40M 7' 5" 8' 10"
20M 3' 9" 4' 6"
15M 30" 36"
10M 22" 27"
They are pretty broadband. I recently made one for 24 MHz that works FB on
15 and 10 meters. I have also used them on six meters on both ends of my
hardline with 1500 watts without any problem.
For 2 meters and above, I try to cut the hardline to be some number of half
wavelengths long - so that the impedance will be the same at each end. You
can test this with an SWR meter with the far end open. Trim the length so
that you have high impedance (>= 1000 Ohms). If you do this, you don't need
to use any kind of impedance transformer. Put 50 Ohms on one end and you
will get 50 Ohms on the other.
73 Tree N6TR
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list