By traditional you mean the coupled wire like a monomatch? Commonly used
for CB meters. It is directional because it combines capacitive and
inductive coupling and produces a DC output proportional to voltage and
current, e.g. watts. Same as the type made by slipping a wire under the
braid. I've used that style to measure loss in a shorted transmission
line by comparing forward to reflected power and came up with value that
matched the coax cable loss tables. I can't subscribe to the voltage
only premise. The inexpensive meters don't have as fine a directivity to
show zero reflected with a perfect 50 ohm load but get in the ball park.
I have a Collins prototype that has functioned perfectly fine on an
antenna tuner for more than 45 years, though it was rejected because the
shielding wasn't adequate to reach the directivity they desired. The
production coupler does meet their wants for 30 dB directivity. On an
ordinary meter less directivity is adequate for my radios.
There are no pass through pseudo wattmeters with directivity that depend
solely on voltage. There have been Bird loads that only measure voltage,
but are calibrated in watts, but then those termalines are a standard of
reference of what a good 50 ohm load should be.
73, Jerry, K0CQ
On 4/25/2010 11:48 AM, N4PY2 wrote:
I said traditional wattmeter. I am referring to inexpensive wattmeters
that only measure voltage.
Carl Moreschi N4PY
121 Little Bell Dr
Hays, NC 28635
www.n4py.com
----- Original Message ----- From: "Dr. Gerald N. Johnson"
<geraldj@weather.net>
To: <tentec@contesting.com>
Sent: Sunday, April 25, 2010 12:35 PM
Subject: Re: [TenTec] OMNI VII vs. K3 ? Opinions invited.,
No, a true wattmeter (Bruene design) takes the vector product of voltage
AND current to produce DC proportional to power.
73, Jerry, K0CQ
On 4/25/2010 11:32 AM, N4PY2 wrote:
In fact it is driviing the load with 36 watts in your example.
When the wattmeter shows forward power of 100 watts and reflected
power of
40 watts into a high swr, because the load is not 50 ohms, the wattmeter
readings are false. Traditional wattmeters are calibrated for 50
ohms. The
wattmeters really only measure voltage and assume the load is 50
ohms. The
100 watt reading in this case for forward power is not correct
because the
load is not 50 ohms. But it happens to work out that the true power
is the
forward power reading minus the reflected power reading. All the true
power
is delivered to the load minus transmission line loss. Transmission line
loss goes up with SWR.
Carl Moreschi N4PY
121 Little Bell Dr
Hays, NC 28635
www.n4py.com
----- Original Message -----
From: "Rick - NJ0IP / DJ0IP"<Rick@DJ0IP.de>
To: "'Discussion of Ten-Tec Equipment'"<tentec@contesting.com>
Sent: Sunday, April 25, 2010 12:20 PM
Subject: Re: [TenTec] OMNI VII vs. K3 ? Opinions invited.,
As always Sinisa, you are correct.
Nice to hear from you again!
The one place I have seen a difference is when trying to tune a linear.
While varying the power on any Ten-Tec, and tuning the amp, it simply
varies
the output power of the amp.
I've had JA makes that seemed to jump around, like they would suddenly
reduce power.
Then I wasn't sure if the input power had dropped or if it was the
settings
of the amp causing the change.
In any case I preferred the way the Ten-Tec tuned.
Now something to think about.
If I run 100w on the Ten-Tec and 40 watts are reflected, then as you
say,
the amp or antenna receive 60w.
If my non TT rig reduces the power to 60w, due to high SWR, it is
putting
out 60W but it is only driving the load with about 40w.
Or is my thinking wrong?
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com]
On Behalf Of shristov
Sent: Sunday, April 25, 2010 9:56 AM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] OMNI VII vs. K3 ? Opinions invited.,
Rick - NJ0IP / DJ0IP<Rick@DJ0IP.de> wrote:
... this full power into 3:1 SWR
Hi Rick,
"full power into 3:1 SWR" is just a myth.
Did you ever read such a claim made by TenTec?
There is nothing inside TenTec transceivers to make them to DELIVER
full
power into a mismatched load.
TenTec transceiver do not DELIVER full power into a mismatched load.
They just fail to reduce the drive with high SWR because they mis
such a
circuitry.
Consequently, the FORWARD power stays the same, at 100 W.
But we must remeber that:
DELIVERED power = FORWARD power - REFLECTED power.
Power meters inside Orion, Omni VII, and virtually all the other rigs
display FORWARD, not DELIVERED power.
With SWR = 3, we have:
FORWARD power = 100 W
REFLECTED power = 25 W
DELIVERED power = 75 W
Similarly, with SWR = 10, we would have:
FORWARD power = 100 W
REFLECTED power = 67 W
DELIVERED power = 33 W
The only thing that can make PA deliver full power into a mismatched
load
is, of couse, a tuner.
TenTec transceivers are no exception.
73,
Sinisa YT1NT, VE3EA
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