Ecoflex 15


Chris Bartram G4DGU
 

Ray,

I had an 'interesting' experience a decade ago attempting to use a long length (~20m) of LDF4-50 on 10GHz. It was used as a temporary replacement for the low-level 10GHz RX feed from my old EME dish. The LDF1-50 I'd originally used became intermittent, and the only vaguely suitable cable I had at the the time was a length of 4-50. The larger cable appeared to work initially, and the insertion loss seemed about right. However, over time the IL varied from far better than seemed possible to enormously large!

My diagnosis was that the cable was supporting (at least!) two propagation modes: normal TEM, as we'd usually expect in coax, and a waveguide mode. As the length of the cable varied with temperature, the two waves travelled along the cable, and interfered with each other either constructively or destructively leading to the large variations (>10dB) in loss. Replacing that cable was to be my next job at the time I had to dismantle the system.

The moral of that story is not to use cables above their design frequency range!

73

Chris G4DGU


Raymond Brooks
 

Thanks Chris,  that's the sort of information I needed,  I'll have to use ldf2-50 with the higher losses until I find a another solution.  

On 20 Feb 2021 09:44, Chris Bartram G4DGU <chris@...> wrote:

Ray,

I had an 'interesting' experience a decade ago attempting to use a long
length (~20m) of LDF4-50 on 10GHz. It was used as a temporary
replacement for the low-level 10GHz RX feed from my old EME dish. The
LDF1-50 I'd originally used became intermittent, and the only vaguely
suitable cable I had at the the time was a length of 4-50. The larger
cable appeared to work initially, and the insertion loss seemed about
right. However, over time the IL varied from far better than seemed
possible to enormously large!

My diagnosis was that the cable was supporting (at least!) two
propagation modes: normal TEM, as we'd usually expect in coax, and a
waveguide mode. As the length of the cable varied with temperature, the
two waves travelled along the cable, and interfered with each other
either constructively or destructively leading to the large variations
(>10dB) in loss. Replacing that cable was to be my next job at the time
I had to dismantle the system.

The moral of that story is not to use cables above their design
frequency range!

73

Chris G4DGU









--
Raymond G8KPS