"Frank Gilliland" wrote in message
...
On Fri, 13 Aug 2004 15:29:17 -0500, "Dave VanHorn"
wrote in :


"Southern Kiwi" wrote in message
...
Can I use my old coax and mounts from my 26 mhz days on a new uhf rig?

Probably, but how much of your signal do you want to waste, heating up the
coax?
With some types, it wouldn't be a surprise to see 3/4 of your power lost
between the rig and the antenna.. Andrews LMR-400 is good, as is all
large
hardline.


If the line is short, the type won't make much difference unless it's
RG-174 (really thin stuff). E.g, for a length of 18' @ 500 MHz I got
the following loss figures:

1/2" HL -- 0.3 dB
RG-17 -- 0.3
9913 -- 0.5
RG-8 -- 0.9

I've seen quite a spread for RG-8, and that's just from reputable
manufacturers, not including "no name" cable.
Try the calculator he http://www.ocarc.ca/coax.htm 100' of 8237 at 4.5dB
loss (over half your signal gone, in both directions btw, or 9913, which is
not bad stuff, at 2.85dB, nearly half your signal gone.. Or 9258 at (gag)
8.28dB loss, and Tandy at 8.03dB! LMR-400 at 2.69

RG-58 -- 1.5
RG-174 -- 4.9


N connectors are much better than the old "UHF" connectors (so
named when 30 MHz was "Ultra-high frequency")

I don't know where you get your information but it's wrong. UHF
connectors work fine for UHF. And to the best of my knowledge, the
current limits of the UHF spectrum (300 MHz to 3 GHz) were defined
long before the connectors ever existed.

By "uhf" I'm assuming he means PL-259/SO239 sorts of connectors, which are
lossy at UHF.
"works" is a pretty sloppy definition. Lots of junk "works".
Works well, is a different story.

Here's one fairly authorative source:
http://www.qsl.net/vk3jeg/pl259tst.html
The charts are somewhat slow to load, but worth it.
Insertion loss of about 1dB, compared to "almost immesurable" for an N
connector.

So let's take my reccomendation, LMR-400 with Ns, 100' at 3dB loss vs
middle of the road RG-8 (not the worst junk) and PL-259s at 6.5dB. So with
1W up the pipe, I get about half a watt to the antenna, you suggest that
1/4 W is ok?

Here's VK3JEG's summary:
I would like to finish with these few points. The first being that the so
named UHF connector from the past is not really suitable for use above 300
MHz at all. Perhaps the exception to this would be when a cheap and rugged
system is required where loss and good signal to noise ratio is of little
concern. Unfortunately it appears that both Amateur and CB Radio UHF type
equipment fall into this category as many manufactures still supply SO-239
UHF receptors as standard equipment. (DVH: I know MANY hams that would take
exception to that!) The second point is that from our results we can see
that utilisation of the UHF connector at 146 MHz for FM type transceivers is
not such a problem. A cheap rugged connector is probably an advantage as
many FM units are used for mobile applications. However, for 144 MHz SSB
type work where low loss and good signal to noise ratio is very desirable,
again I would not recommend the use of UHF type connectors. The UHF
connector still has a place in many applications where a robust economical
RF connector is required but for serious applications its use should be
limited to below 100 Mhz. As we have shown the N type is far superior in
performance, it should also be noted the BNC type connector is similar in
performance to that of the N type but has the disadvantage of being less
rugged. In the end, one should always check with the manufactures
specifications.