[time-nuts] Thunderbolt setup

Chris Albertson albertson.chris at gmail.com
Wed Mar 16 16:59:25 UTC 2011


On Wed, Mar 16, 2011 at 4:51 AM, Bob Camp <lists at rtty.us> wrote:

> The wonderful thing about a TBolt is that it can use foam core TV satellite coax. Since 75 ohms is lower loss than 50 ohm (all else being constant) you can get away with quite a bit of the stuff. F connectors are easy to do wrong, so get some good ones and a proper crimp tool.  Most antennas are TNC or N, so you will need an adapter. Again - get a good one.

What you really care about with antenna cablbe is the total loss.
Given the gain on the antenna and the requirements of the t-bollt
reciever you have a budget in dB to work with.  Stay within budget.

Loss comes from two things (1) any cable will have a loss measured in
DB for foot at the 1.5GHZ frequency.  This and your budget will limit
the length of cable you can use.  If a given cable type has to much
loss then you need to buy the more expensive kind.  If you are lucky
you might be able to use that cheap RG8 cable TV stuff but if you have
a lower gain antenna and a longer run of cable then you might need
LMR400 at 4X the price.   All that matters is that you keep the loss
in-budget.    (2) connectors and adapters have loss too.  You get the
least loss by using the correct ends on the cable so no adapters are
required.   It all depends if you need to care abou the last dB of
loss or not.

I think the best setup is to put a 1" iron pipe on the roof that is
taller then any other vents or pipes up there but not so tall you
can't reach and work on the top.  Mount the antenna on that pipe and
run the cable trough the pipe, through the roof and then straight down
to the living space in the house.    Ideally the antenna cable run
would be a short perfectly vertical run but that is unlikely.  But
still you want the t-bolt in the living space and the antenna high on
the roof and the cable run minimized.

Once you know the length of cable then you can decide on the lowest
priced cable that still has a low enough loss.

-- 
=====
Chris Albertson
Redondo Beach, California



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