I cannot recommend a specific cable. But I will say that RG58 is 100%
non suitable for use at 920 MHz! RG58 has very high loss and even 100
feet at 920 MHz will loose about 96% of the received signal [-14 dB].

RG8 or RG11 will loose about 1/2 of the received signal. RG8 or RG11
will cost about $0.50 [USD] per foot. Good quality connectors will have
to be used.

Mark wrote:

Please could somebody tell me the best cable (compromise between cost
and loss) for use with an external Yagi antenna connected to a mobile
phone. I live in a Very poor reception area, and I need to fit an
external antenna. I have found somewhere that sells 10 element Yagi's,
and I can mount the thing as high as need be, but I read somewhere
that the longer the connecting cable, can negate the benefits of long
mounting poles. I have freinds in the surrounding area that have the
same problem, so I could do with a "rule of thumb" that I can use for
fitting these things. The shop where I got the antenna from is
offering me RG58 cable for this purpose, which is cheap enough, but is
it the best compromise for what I am trying to achieve? Your
assistance would be most welcome.
Mark