You would be amazed how many LNA's have a POSITIVE Return Loss.i.e. more comes back than goes in!??? Kent WA5VJB
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On Tuesday, September 29, 2020, 11:59:27 AM CDT, Jim Lux <jimlux@...> wrote:
On 9/29/20 9:27 AM, Jerry Gaffke via groups.io wrote:
I would think attenuators and booster amps may as well be in the external cables.
Not terribly familiar with all this, perhaps there are special tricks involved to measure
something like s12 on an amp?
Oohh. that's everyone's first guess.. but think about it.. if you want
to measure the S11 of a LNA, you can't put 50dB of attenuation in front
of it.? You put 50 dB of attenuation in the stimulus line, then the
bridge, then 50dB of amplifier in the receiver line.? Then calibrate as
per usual.? If your receiver has good dynamic range, you don't need as
much amplifier.
Adding them to a $300 VNA board adds complication and sources of trouble.
Modular is good when it comes to seldom needed features.
True - maybe a different version of the board, that just leaves out the
resistive bridge.? And some extra SMA connectors
The ability to use a different bridge would be interesting.
Perhaps lay out the board such that? one could insert vertical SMA's
and stir some surface mount parts to accommodate this?
Yet another product variant for Hugen to sell at some time in the future.
But I suspect most nanovna users have never felt the need for an external bridge.
Requiring an external bridge for all work with the VNA is perhaps a bridge too far
towards modularity.
Typically, the way it's done is to have two connectors with a removable
jumper between them.
I would venture that for most VNAs that have this, the jumpers have
never been removed except when doing factory cal/re-cal.? Or when
someone sets the VNA down on a non-smooth surface and breaks the jumper.
Jerry, KE7ER
On Tue, Sep 29, 2020 at 08:47 AM, Jim Lux wrote:
yes, it's going towards the fieldfox type of capability, not the "bench VNA" -
The latter would typically bring out the source and receiver inputs with a
loop, so you could use different bridge or insert attenuation to make it
easier to test amplifiers.
This design has a 30dB sep attenuator, but still, if you're testing a LNA with
a maximum input of -70 dBm (because it's designed to receive signals at -150
dBm) this probably isn't your box of choice. Assuming he's putting +10 into
the attenuator, the output power will be -20 dBm or around there. That's
enough to saturate a lot of LNAs.
Likewise, if you were testing a 10W PA, you might want a booster amplifier in
the drive on port 1, and an attenuator in port 2.
