[TowerTalk] Fiber optics for amateur radio..

[Richard (Rick) Karlquist]

Jim Lux wrote:

> 
> 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.. 

I used to design fiber optic communication test equipment at Agilent,
up to 40 Gb/s or so.  We looked into sending analog signals optically,
but all the optical hardware is now highly integrated assemblies that
are designed to send digital signals only.  The closest you could get
to analog transmission would be to frequency modulate an oscillator with 
your spectrum and then FM demodulate at the other end.  You might
as well just digitize the spectrum in that case.

> 
> 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 already run CAT5 (6 cents a foot new at Fry's) to my tower and only 
have the heavy duty stuff running up the tower.  K7NV sells a remote 
rotor controller to do this.  Using Power Over Ethernet, you can use
CAT5 for both signalling and moderate amounts of power.  To remote
a linear, this is the strategy I have arrived at:  Step up
the power voltage to 480 VAC using a 5KW isolation transformer
wired as an autotransformer.  At the linear, step it back down
to 240VAC. I have several of these transformers that people
gave me for free, if I could haul them away, hi.  This allows me to
use fairly small wire.  But the other magic bullet is to get a
solid state linear with a "Universal" switching power supply.  These
supplies automagically run on any voltage between 85 and 260V.
Thus it doesn't matter if the line voltage at the linear sags 10%
or 20% on key down.  The output is always 48V.  Another strategy is
to put batteries at the linear and only use the connection to the
power company for charging them.

Rick N6RK





> 
> 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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