The main problem with this power measurements is that also if the
power meter and the attenuator are in good condition the
measurements can be vary a lot.
The reason is that a HT has in most cases not a true 50R output
impedance.
So if you connect the HT output to a load you have reflections
that can bring very big errors to the measurement.
This is the reason why I always use a feed through power sensor,
like the BIld or the R&S with a very very short connection to
the HT and after that a directional coupler with termination and
the SA.
So you can measure the real power much better.
Also it isn't in most cases of real help to know the output power
of a HT, because a HT is always a more or less matched pair with
the antenna. So what of real interest is, is the transmitted
energy, that is influenced by the surrounding environment a lot. A
good HT has a tolerant output stage that can handle a lot of
impedance fluctuations without producing distortion and noise.
Nothing that can be measured with a power meter or an SA by
themself.
A nice test setup is using a length variable stub to make a?
variable complex load and look what the power, the spectral purity
and the power consumption is doing. And then repeat this with a
whip antenna instead of the dummy load.
I have done some measurements with a 2m HT standing free, holding
with the hand, holding near the mouth, inside the pocket. After
this tests it was clear to me why a good old Motorola GP900 had a
better real live performance then a cheap HT. It is some years ago
that I have done that, but the basics don't change. Also I prefer
to use singe band low bandwidth HTs for real work. The receivers
are much better regarding out of band sensitivity.
When measuring whip antennas it is necessary to build a
counterbalance to the antenna. A can with a socket soldered inside
and a common mode filter on the feed cable is a good start.
One more point is that because of the unknown source impedance it
is possible that the meters show different values because they are
often not power meters, they are voltage meters with a 50R
resistor.
To conclude this. You can't use a HT as a measurement source if
it isn't carefully measured and specified for its behavior. At
minimum add a 3 dB attenuator directly without adapters to the HT
output to make the source impedance better, 10dB if you can
compensate that power loss in your measurement chain.
All the Best,
Isidro
Am 13.12.2022 um 17:25 schrieb hwalker:
On Tue, Dec 13, 2022 at 06:41 AM, John AE5X wrote:
On Sat, Dec 10, 2022 at 08:16 AM, Erik Kaashoek wrote:
You can check your attenuator using the tinySA.
I never would have thought of using the CAL function in this
manner - works like a charm:
?
John,
? You can also measure the attenuation without the math by first
normalizing the CAL output signal as below:
CALOUT: [email protected]
?
TRACE1->NORMALIZE
?
20dB Attenuator between CAL OUT and RF IN.
?
Herb
