[TowerTalk] 75 ohm hard line

Mon Aug 30 09:45:00 PDT 2010

Dick,

   I use 75 ohm line here for 144 and 432.  In the past I used it on a HF
tri-bander with excellent results and I used a 1:1 balun up top and just
retweaked the antenna matches accordingly.  

   For your design, have you considered putting a couple 50:75 UnUn's in
there?  You can HB it or several companies offer a turn key solution...

73  Mike K9MK

-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Dick Dievendorff
Sent: Monday, August 30, 2010 11:19 AM
To: towertalk at contesting.com
Subject: [TowerTalk] 75 ohm hard line

I've been offered a quantity of CATV 75-ohm hardline.  

The radio room will be about 120 feet from the base of the tower, and the
highest antenna on that tower will be at 77'.  The antennas on this tower
are 40, 20, and 15 meter wide-band yagis.

I'm trying to figure out what I need to consider when contemplating antennas
and radios designed for 50 ohms with 75 ohm feedline.    I'm worried not so
much with power loss caused by the impedance mismatch, but the effort
required to show the rig a 50 ohm load on various frequencies.

The antennas on the tower are 50 ohm OWA antennas that were selected to
avoid the need for an antenna tuner, a complexity I'd prefer to avoid in a
high power SO2R contesting environment. 

Another antenna a little further away is a HyTower, and I expect to use an
ATU for that one.   But I'd probably use it on 75 and 160 mostly.

I think I'm probably better off with a couple of runs of LMR-600, but I
thought I'd ask for suggestions before turning down the hardline offer.

I plan a K9AY receive loop fed with 75-ohm line some distance (less than 500
feet) away.  Should I bother with hardline for something like this?

Dick, K6KR

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