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