Yes, Tom is correct-- it's entirely possible a second attenuator
is needed on the VNA's receiver S21 port to prevent overloading
the VNA. The specs of the VNA should state the max S21 input.
The other consideration is not overloading the preamp DUT--input
impedance S11 and gain S21 will not be correct if the DUT is
overloaded. I like to ensure the DUT test output is not much over
0 dBm--a decent preamp should not be overloading at that level.
The ALA1530LN has about +22 dB peak gain--so for 0 dBm output that
would be -22 dBm input. Most of the inexpensive nanoVNAs have a
fixed transmit S11 output, usually in the +10 dBm to -10 dBm
range--the VNA specs should tell what that level is. Knowing that
along with the DUT gain, you can get an estimate of the input
attenuator required.
73,
Steve AA7U
On 1/4/2025 5:10 AM, Tom ANderson via
groups.io wrote:
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?Francesco,
I
want to say I might be wrong here so, please double check
me.
In
your drawing you show the 20db attn connected to the input
of the amp I assume this is to prevent over driving your
amp. ?However, you do not have an attn on the output side.
Is
this accurate? ?
I
have read that you will damage your VNA if you apply too
much of an input. S21 port, So in my mind, you should have
an attn on both the input and output to protect the VNA? ?If
this is not necessary please let me know.
Good
luck in your efforts?
?
Tom
Anderson
SDR_Radio@...
On Jan 4, 2025, at 6:03?AM, Francesco
Caizzi via groups.io <netsmo62@...>
wrote:
Francesco
