[TowerTalk] Hardline ?

[Gary Schafer]

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Jim Brown
> Sent: Thursday, May 07, 2009 3:14 PM
> To: Tower Talk List
> Subject: Re: [TowerTalk] Hardline ?
> 
>  Gary asked:
> 
> >> I hate to start something here,, but where does the "0.18 dB additional
> loss
> >> come from with any length of line"?
> 
> I responded:
> >>
> >> There's an equation in the ARRL Handbook and in the ARRL Antenna Book,
> and
> >> there are graphical plots of that equation for various values of
> mismatch and
> >> matched loss.
> 
> >> On Mon, 20 Apr 2009 18:08:39 -0400, Gary Schafer wrote:
> 
> >That is not applicable to this situation:
> 
> It's been so long since the original post that we may have forgotten what
> "this
> situation is."  As I recall, the original post was concerned with the
> additional
> loss in 75 ohm hardline over 50 ohm hardline when the impedance of the
> antenna
> was 50 ohms. I could be mistaken about that, but that is the question I
> was
> responding to.:)  The worst case ADDITIONAL loss in the line for this
> degree of
> mismatch is 0.18dB, no matter how long the line is. This is shown in the
> graph
> for that degree of mismatch, which is asymtotic to 0.18 dB.

Hi Jim,

I see where you are coming from now. In my last response I thought that you
were talking about loss because of a mismatch to the generator and the
generator could not put out full power because of it. I didn't look at what
you referenced.

What I was originally questioning was your first statement (long ago) of
"0.18 dB additional loss with any length of line" when 75 ohm line was used
rather than 50 ohm line. I don't think that you originally said "worst case"
as you now have. I may have missed it originally though.

That sounded like you were saying that there was an automatic .18 dB of loss
when there was a 1.5:1 mismatch no matter how much loss the line had. 
That is why I said that you must first know the line loss in order to
determine the additional loss caused by the mismatch.  
However, I agree that the MAXIMUM additional loss in this case of .18dB
seems to be correct but it will be less than that when line losses are
lower.

73
Gary  K4FMX