[TowerTalk] Fiber optics for amateur radio..

David Robbins K1TTT k1ttt at arrl.net
Tue Dec 4 06:32:23 EST 2007

Fiber is nice for transmitting control and data information.  It of course
is a bit more complicated than just running copper with the same
information, but has advantages of being less susceptible to rfi.  There is
one big thing that everyone forgets though, you can't transmit POWER via
fiber.  You want to turn a rotor via fiber?  You have to run copper to the
rotor for power, need relays or some other electronic converter to take the
control from the fiber and convert to signals to turn on the relays.  So you
have taken what was a simple copper wire from a simple supply in the shack
and added at least 2 more complex (relatively) opto-electronic converters.
Want to get position indication back?  You need another fiber (or you could
re-use the same one at the expense of more complex converters), some kind of
digitizer or analog to fiber converter, calibration, and decoding to some
kind of display in the shack... much more complex and prone to failure than
a simple copper connection from a pot to the meter in the box.  Want to put
the rx/tx up the tower and feed by fiber... great, no feedline loss, but you
still have to run power up the tower to the box with the fiber so you still
have to worry about lightning protection, but now its in the direct line of
fire on the tower.  And it has to be all remotely controlled via fiber...
final transistors fail in the middle of a contest???  Can't just pull a
spare rig off the shelf and plug it in, you have to drag it up the tower.  

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Jim Lux
> Sent: Tuesday, December 04, 2007 01:23
> To: towertalk at contesting.com
> Subject: [TowerTalk] Fiber optics for amateur radio..
> I just got some SMA:UHF adapters from L-com, and they had their catalog in
> the box, which I browsed through desultorily, prompting the interesting
> observations...
> Fiber optic cabling is getting pretty commodity and inexpensive.  A 20
> meter dual fiber patch cable is about $35 (the pricing looks like about
> $20-25 for the connectors and assembly, plus a length dependent addition
> for raw cable).  Couplers to join two cables are in the $3-$5 range.
> Ethernet to Fiber converters are about $75-200 depending on environmental
> needs (waterproof ruggedized ones cost more)
> The mouser catalog has Amphenol fiber assemblies for about $13 for a 20m
> long dual cable with LC connectors.
> I haven't browsed through the Mouser or Digikey catalogs for this, but it
> seems that there must be analog transmitter/receiver components that are
> fairly inexpensive for HF thru UHF use (I know there are microwave links
> for fiber from Ortel, etc., but they arent' cheap)
> I wonder what it would take to build a HF preselector/amplifier/fiber
> transmitter and corresponding receiver.  You could put the widget up the
> tower, and completely eliminate the whole "feedline as a radiator" or
> "feedline carrying lightning" issue.  This is a receive kind of
> application.. It's probably a bit bold to suggest putting your kilowatt
> linear up the tower, but the idea is there..
> Or, for relay/tuner controls...
> A complete link is still in the $200 range (2 ends+cabling) but that's not
> totally unreasonable.  For instance, if you had to string several hundred
> feet of multiconductor rotator or SteppIR controller cable.. copper prices
> are rising
> For instance, 10 conductor AWG22 cable runs about $1/ft these days (Mouser
> catalog page 904), so a 300 ft run is going to be $300.  Compare that to a
> couple 75 dollar boxes on the ends and a cable at $20-30.. Browsing page
> 2075 in the catalog, it looks like the low end cables are about
> $0.03/ft....Single mode (higher data rate) runs about $21 for a 20m cable
> and $16 for a 10m cable ($5/10m or $0.15/ft for the cable)
> I've also started to see this kind of thing showing up used/surplus (when
> they refurbish a business/commercial property, and pull the existing
> cabling infrastructure out).
> Maybe we need to start pushing the mfrs to build rotators, relay boxes,
> and stuff with fiber interconnects.
> Has anyone seen something like a "fiber to relay contacts" box?  (sounds
> like a good QST project).
> (for short range.. the TOSlink plastic optical fibers like are used on
> audio gear are really cheap.. the LED and/or detectors are about $1
> each... Cable is about a buck a meter in small quantities.)
> Jim, W6RMK
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