On 1/7/16 6:53 AM, n8de@thepoint.net wrote:
Why the 4-wire control cable?
You can use the coax for switching ... I invented the idea in the
70's... it's very much like what is in the ARRL Antenna Handbook (and
the ARRL Handbook) ...
similar switching is available from MFJ/Ameritron .. and was used by
Drake and Heathkit years ago.
Just need to build a small blocking circuit at each end of the coax.
I think it's more to power/control the AH-4.
Power is easy - "bias T" on each end.
Control less so. I don't know enough about the AH-4 and what it
needs/sends back to the radio. The "send AC and use diodes" approach
gives you 4 possible states, so that might be enough for the AH-4 (I can
see needing "power" and also needing to "push" a "tune" button)
On the other hand, if you want something that is basically plug and
play, a siamese cable with the right connectors on each end is a lot
simpler.
The MFJ Bias T is $30, and you need two. $60 would pay for a pretty
fancy cable ($1/ft)
If you were running hundreds of feet, it might be more worthwhile.
I've gone through several different iterations of "how do you control a
remote antenna tuner or switch", and for a short distance, the easiest
and simplest solution is "run separate wires".
It's when you get to "I want to do a phased array with 6 elements and
switching at the antenna and it's 1000 ft from the shack" that solutions
like "send DC along with 2.4GHz WiFi over the coax" start to be
attractive. And they are more complex.
For what it's worth, if you're in a major city, there are companies that
will make custom cables: basically taking a bunch of standard
wires/cables, and putting a custom jacket around them. Last time I
checked (15-20 years ago) it was in the $1-2/ft range, depending on
whether you wanted something hotstamped on the jacket (e.g. W6RMK super
cable 42) and what the material was (PVC, PE, Urethane). That was for
small quantities (100ft).
For instance, we were looking at getting custom extension cords made
with the company name on them and in an unusual color so that they
wouldn't disappear at job sites. We also looked into getting custom
cables with LV AC power+Cat 5+coax to reduce the rats nest problem in
field/location work.
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