[Elecraft] Coax Loss Figures

[Brett Howard]

I was starting to look at connectors when comparing getting adapters to
use the LMR600 that I have to that of using LMR400 that I have with the
right connectors on it already...

>From what I've seen in other models I'm expecting 7:1 SWR on 20 and 3:1
SWR on 40 with the 4:1 UNUN that DX recommends to help make things tune
easier.  

When Elecraft makes me a remotable tuner that will work with my setup
then I'm game... Till then I'll suffice with the tuner thats built into
the radio.  It should be able to handle most of what I should see with
that 4:1UNUN on there and its capability of tuning things w/in 10:1...
I'm not holding my breath for using it on 80Meters but we'll see what
the tuner can handle...  I plan on setting things up on Friday and
taking my notebook and collecting a bunch of data on it to see how
things shake out...  

I'm not expecting magic I'm just trying to get my head around all the
math and get an idea of what I should expect so I know when to be
surprised and ask questions when reality doesn't match theory... ;)

~Brett (N7MG)

On Wed, 2010-06-23 at 03:15 -0400, Tom W8JI wrote:
> > Well heck if LMR400 is .7dB/100ft I'm not so sure that its worth mucking
> > with finding adapters for it as if I end up having to put 2 adapters on
> > each end to get it to something I can use there goes most of my
> > advantage of stepping up from LMR400 to LMR600...
> 
>  The loss in connectors or adaptors at HF or even up into VHF is virtually 
> immeasurable, unless they are simply terrible. If the connectors are 
> terrible you might have 0.05 dB loss.
> 
> A common SO-239/PL259 junction has less than .02 dB loss at upper HF.
> 
> I'd be more concerned with transmission line losses due to SWR on the 
> transmission line and voltage breakdown of connectors in your application. 
> Here are the peak voltages at the antenna base with only 100 watts applied 
> at the antenna, and the losses in a feedline using 100 feet of LMR500:
> 
> 160= 4800v  (>100:1 SWR) 16 dB feedline loss
> 80  = 1000v (>100:1 SWR) 6 dB feedline loss
> 40 =  215v (5.4:1 SWR)   .6 dB feedline loss
> 30 =  500v (26:1 SWR) 3 dB feedline loss
> 20 =  540v  (29:1 SWR)  3.5 dB feedline loss
> 15 =  280v (9:1 SWR)  1.7 dB feedline loss
> 
> Why would you worry about connectors when 100 feet of LMR500 would have 
> losses like that? Put a tuner at the antenna base if you want to reduce 
> losses.
> 
> 73 Tom 
>