Topband: Receive antenna switching - Thanks!
Richard (Rick) Karlquist
richard at karlquist.com
Wed Aug 5 09:01:23 PDT 2009
R. David Eagle wrote:
> I just wish someone made something similar in a cheaper kit fashion.
This is one thing that has really surprised over the years is why no
one has come out (commercially) with a decent switching design (>4 ports)
that utilizes the coax for long runs rather having to drop a control
line to the switch.
A contrarian view here. I have 20 acres to fill with antennas
(an acre is a terrible thing to waste :-), so I
have my share of long feed lines. After experimenting with sending
DC and control signals over coax, I have come to the conclusion that
it is often easier IMHO to just make a parallel run of CAT5 cable for
DC and control purposes instead of spending a lot of time engineering
DC/control over coax systems. You can get CAT5 for ~5 cents a foot,
depending on your scrounging abilities. The extra work to run CAT5
along side the coax is far less than the work to build tricky control
circuits. And if the control circuits were available commercially,
it is a safe bet they would cost more than the CAT5.
It reminds me of when I worked for Hewlett Packard Laboratories
and we were trying to invent a wireless link to go from computers
to printers. We got a reality check when the business people told
us that the most anyone will pay for a wireless connection to
a printer is the cost of a printer cable (this was before wireless
LAN's that made all this moot).
The real deciding factor to me was the discovery that if any water
gets into the coax anywhere, if there is DC on the coax, there will
be a small DC leakage current that generates 40 dB over S9 noise.
All it takes is one nick, or one bite by a critter and some rain.
Maybe I should have used flooded coax, but I got several miles of
new coax for $1 a pound which is not of the flooded type.
Another issue is that I want FAST switching between beverages in
contests. This tends to work against methods like DTMF that have
a time delay.
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