[Elecraft] Re: "good quality coax," important? depends

[Indy]

> I see many references to "good quality coax" including in the KAT1
> instruction manual. I'm not sure how to tell "good quality" from the
> "rubbish". I have a pile of RG58, 5mm OD stuff that is cheap (got mine
from
> Electrovalue in UK). Is this good enough for QRP on 40-15m? . The 213 coax
> is much bigger, heavier and expensive.  If I use RG58 and provided I don't
> have long lengths with high SWR I don't think I shouldn't have big losses
> (I am putting up a 40m dipole). Some coax in the UK is advertised as
> "military spec" presumably this is better but in what way?

Personally, i wouldn't use either of those coaxes, but you could use them,
depending...

Loss plummets as frequencies drops below 30 mhz.  Loss plummets as length of
coax is reduced.  Loss falls, not as significantly as the preceeding, as SWR
is reduced, and loss from SWR is insignificant if the coax is short or the
frequency low.  Therefore, there are at least four relevant components to an
answer for your question:

1)  coaxial loss ... this has to do with the quality of the coax.  What is
good quality coax?  Ask for the loss per hundred feet.  Expensive coax is
better and thicker is better.  My favorite is RG-8X for realtively low loss
versus light weight and flexibility.

2)  how long will the coax be?

3)  what frequency will it be used on?.

4)  what SWR, will it be a 50 ohm antenna or not?

The longer the coax will be, the more significant it is to have good quality
coax.

The higher the frequency will be, the more significant it is to have good
quality coax.

The higher the SWR will be, the more significant it is to have good quality
coax (SWR in of itself is NOT a loss).

If the coax will be 25 feet long and the antenna is matched, and you are
using it on 10 meters or below, no worries.

If the coax is 100 feet long, the antenna is not matched, and you are using
it on 20 meters or higher, you better be using good coax.

When i am operating portable using a G5RV 10-40 meters, for example, my coax
is 15 feet long.  I am not concerned about SWR, or loss of any kind.  I
would not hesitate to use RG174 in this case, but I generally use RG-8X.

73,

Fred
kt5x