This sounds similar to some cable I got surplus a number of years ago.
The loss was surprisingly high at 7 MHz. I'm quite sure the reason is
that the center conductor is made from several strands of very fine
copper-clad steel wire. Although the copper is probably a sizeable
fraction of the overall wire thickness, it's still thin in terms of skin
depth at the lower part of the HF region because of the very small
strand diameter. Consequently, significant current flows in the steel,
which is very much more resistive than copper at HF. Loss at VHF is
about what you'd expect from a copper center wire.

So I recommend checking the loss before using the cable at HF if loss
might be important to the application. I used it as low-weight feedline
for Field Day (I generally backpack my FD gear), and was prepared to
accept the loss I thought it would have as a trade for the low weight.
But I found the loss to be considerably greater than expected.

Roy Lewallen, W7EL