LMR-300 would do the job for a price:

COAXIAL CABLE - ATTENUATION POWER
HANDLING CALCULATOR

Coaxial Cable Data
Product:
Frequency (MHz): 968
Run Length (Feet): 26
« Reset Calculate »

PRODUCT PERFORMANCE PARAMETERS
Attenuation: 6.3 db/100ft 20.6 db/100mtr
Average Power: 0.35 KW
Cable Vg: 85 %
Nominal Td: 1.2 nSec/ft 3.92 nSec/mtr
Capacitance: 23.9 pF/ft 78.4 pF/mtr
Typical Connector Loss: 0.06 dB/pair

CABLE ASSEMBLY PERFORMANCE
Cable Run Attenuation: 1.6 dB
Total Cable Assembly Loss: 1.9 dB
Cable Run Efficiency: 68.6 %
Cable Run Time Delay: 31.08 nSec


As far as RG 58 is concerned, forget it for
that length.

At 13:13 05 March 2016, Andrzej Kobus
wrote:
On Friday, March 4, 2016 at 8:30:10 PM
UTC-5, George Haeh wrote:
I've been looking into ways to secure
coax=20
inside the tailboom. My current avenue
of=20
investigation is using magnetic
receptive=20
rubber sheet.=20
=20
Wrap a strip of sheet around the coax
with=20
appropriate (suggestions welcome)=20
adhesive and use magnet on exterior
of=20
tailboom to clamp at appropriate
locations=20
well clear of elevator pushrod.=20
=20
Times Microwave has a coax cable
and=20
attenuation calculator:
=20

http://www.timesmicrowave.com/calculat
or/?

productId=3D38&frequency=3D1090&runL
ength
=3D26&mode=3Dcalculate#form
=20
Extra coax length is necessitated by tilt
up=20
instrument panel.=20
=20
I'd also like to to put a
PowerFLARM=20
dipole in the fin, but that would have to
be=20
at least a foot from the xpdr
antenna.=20
=20
The battery box is not big enough for
both; =20
so may need an opening in the box
to=20
achieve enough separation. Once in
use=20
for antenna(s), likely the box would
no=20
longer be available for ballast.=20
=20
If the front of the nose cone, would
work=20
for an L2 antenna, the problem would
be=20
much simplified.=20
=20
Any interference with the comm
coax=20
and/or antenna would mess things up.

George, I am afraid the coax cable losses
for Flarm antenna would be too
hi=
gh if you run it from the tail of your glider
to the instrument panel.
Flar=
m is a very low power unit and the cable
length is very important. Also if
=
the horizontal stab is carbon that would
not work very well either.