nuckolls.bob(at)aeroelect
Guest
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 Posted: Tue Jan 24, 2017 3:06 am Post subject: iCom Antenna Switchbox effect on Com Radio |
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At 05:27 PM 1/23/2017, you wrote:
| Quote: | iCom makes a little box for allowing com antenna to be used by their handheld radio, in the event the primary com fails. This requires splitting the coax from the com transceiver to the antenna into two lengths.
My question is, will using this box have a negative effect on either reception or transmission of the com radio? (as compared with identical system with just an unbroken coax from transceiver to antenna).
Here is a link to the iCom box on Aircraft Spruce:Â http://www.aircraftspruce.com/catalog/avpages/icomswitchbox.php?clickkey=3576 |
King Radio did one of these too, many moons ago.
http://tinyurl.com/zympb82
Icom came along later with their version. I'm
mystified as to where the designer's head was.
They had little if any appreciation for the
value of conserving space and volume.
I purchased one of those some years ago and did a teardown.
The jack is a simple, closed circuit monophonic audio
jack of rather flimsy construction.
http://tinyurl.com/gsatjvz
http://tinyurl.com/j9qwrjj
Pardon my 'french' but that little box is a piece
of you-know-what. In answer to your first question,
that box is 100x more likely to disable your panel
mounted radio than it is to be your communications
salvation for pressing your hand-held into service.
Qualities of the audio jack not withstanding, the ICOM
design made no effort to maintain coaxial feedline
integrity. It's also unnecessarily bulky. I went to
the bench and fabricated this alternative
http://tinyurl.com/jyhzgyf
It has a few redeeming qualities over the ICOM
product but was difficult to build . . . decided
not to propose it.
In the mean time, conversations with folks here on
the List evolved this idea: First, it would be nice
if the external antenna feed line made a more graceful
integration with the hand-held.
http://tinyurl.com/jpccdkz
http://tinyurl.com/zrxsvc3
http://tinyurl.com/h5pd4vo
Some coax fittings and a rubber-band helps to dress
up the interface.
Breaking into the panel radio's coax offers
several options. First, you need a coax
joint in the feed line that is accessible
to the pilot. This means a mated pair
of connectors like this . . .
http://tinyurl.com/h2p7ww4 or this . . .
http://tinyurl.com/jug4864
on the radio side of the junction
mated to this . . .
http://tinyurl.com/grcap2r
. . . on antenna side. Some builders have
installed a 'service loop' of extra coax
coiled up and held in place with velcro-ties.
When the junction is opened, the extra
coax is easily extended to go up the back
side of the radio to the collection of
adapters cited above.
Alternatively, one could use a short
extension cable . . .
http://tinyurl.com/je4xyyg
but this means another piece of 'loose
gear' in the cockpit. But it could be
stored in the flight bag with the radio.
There are many articles on aviation websites that
speak to this topic. Here is but one . . .
http://tinyurl.com/hq9a7zx
Bottom line is that hand-held performance is no
better that the weakest link in the propagation
of energy between your radio and the radio at
the other end. Giving a hand-held radio access to
the ship's external comm antenna with a minimum
parts count and maximized feed line integrity is
a GOOD thing.
This posting could be easily ported to a
"Shop Notes" article on the website. I'll
let you guys have first crack at it.
Bob . . .
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