On 20 mayo, 04:46, walt wrote:
On May 19, 7:33*pm, John KD5YI wrote:



On 4/25/2011 7:35 PM, Sal M. Onella wrote:

This group has presented members with valuable lessons in antennas and
transmission lines, like how to measure, how to match, etc.

Something I haven't seen is a discussion of the source impedance of
the transmitter. *My curiosity was piqued today as I took some baby
steps into EZNEC. *A particular antenna had such-and-such VSWR if fed
with a 50-ohm cable and a different value if fed with a 75-ohm cable.

While this is hardly news, it got me wondering whether a 75-ohm cable
will load the transmitter the same. *Doesn't seem like it.

My point: *Using 75-ohm cable to improve the match at the antenna
won't help me *... IF ... I suffer a corresponding loss due to
mismatch at the back of the radio. *My HF radios, all solid state,
specify a 50 ohm load. As necessary, I routinely use an internal
autotuner and either of two external manual tuners. *(I'm aware of the
published 1/12 wavelength matching method.)

Wisdom in any form would be appreciated. *Thanks.

"Sal"
(KD6VKW)

Hey, Sal -

Lots of good stuff he

http://www.vk1od.net/

Fun reading.

Cheers & 73,
John

Wim, in your calculation of PA output resistance via load pull, you
state:

"...load pulling with 51.2 Ohms and 44.6 Ohms:
V_out (51.2 Ohms) = 71.5V, I_out = 1.396A
V_out (44.6 Ohms) = 66.5V, I_out = 1.491A
Delta_V = 5.0V, Delta_I = 0.095A,
Hence Rout = 52.6 Ohms."

The following is what I obtained through actual measurement via load
pull:

Vout (51.2 ohms = 76.9v, Iout = 1.502a
Vout (44.6 ohms) = 71.6v, Iout = 1.605a
Delta V 5.3v, Delta I = 0.1034a
Hence Rout = 51.2 ohms

Wouldn't you agree that my measurement method and procedure are pretty
well on track?

Walt

Hello Walt,

If you would read again my posting (you removed my source
description), I didn't refer to your actual measurements, but referred
to your measurement method applied to my source example (my source
example is 100Vp in series with -j50 Ohm).

I hope this makes clear the differences.

Wim
PA3DJS
www.tetech.nl

I was taught that by convention, i.e. by definition, the missing power
was never generated in the first place - always seemed like a copout
to me. :-)