[TenTec] Ten Tec 238 coupler and 160 meters

[Joel Hallas]

This is an interesting point, and Steve has recently made a believer out of
me!

The primary transmission loss component at HF, and even more at MF, is IR
loss. With high SWR on the high-impedance side, the IR loss is less than
with a matched condition since the R is the same but the I is less. 

At VHF, depending on cable type, the dielectric loss gets more important,
and will have a larger influence -- but not on 160 M.

Of course, many short 160 meter antennas have a very low Z, and thus this
case is not relevant, but that doesn't keep Steve's assertion from being
correct, and worth keeping in mind--SWR isn't the whole picture.

The conclusion is that the popular graph of "additional loss due to
mismatch" in "The ARRL Antenna Book" for many years is really "average
additional loss due to mismatch for cables much longer than a wavelength"
over which both high and low current conditions will exist.  

Regards, Joel Hallas, W1ZR
Westport, CT

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Carl
Moreschi
Sent: Saturday, November 09, 2013 5:14 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Ten Tec 238 coupler and 160 meters

That's a new one on me.  How could loss be less with high SWR on a short
length of coax?  It makes no sense.

Carl Moreschi N4PY
58 Hogwood Rd
Louisburg, NC 27549
www.n4py.com

On 11/9/2013 5:07 PM, Steve Hunt wrote:
> Interestingly, when using *short* lengths of coax the loss can be 
> lower at high SWR than when it's matched. For example, 10ft of RG213 
> has a matched loss at 1.9MHz of 0.03dB; but terminated with 500 Ohms
> (SWR=10:1) the loss is only 0.012dB - less than half. For a 2500 Ohm 
> load (SWR=50:1) the loss is 0.046 - only 50% above the matched case.
>
> It's only true for high impedance loads and short lengths, where only 
> a small portion of the standing wave pattern exists; but they could be 
> the conditions in this case.
>
> Steve G3TXQ
>
>
>
> On 09/11/2013 21:10, Carl Moreschi wrote:
>> How much coax did you add? The main idea of open wire line is it is 
>> much less lossy than coax at high SWR's. You therefore want to keep 
>> the coax portion is short as practical. The SWR on the feedline could 
>> be 100 to 1 or even higher.
>>
>> Carl Moreschi N4PY
>> 58 Hogwood Rd
>> Louisburg, NC 27549
>> www.n4py.com
>>
>
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