Hi William ... of course the "squared BIAS" I Drawn is just the one made with the BY1-1F ... there is no any other Bias ...
I was asking WHY the INPUT Resonance changed as soon as I apply Power-Supply (and consequentely the Bias) ....
I was just a question ...
Peter.
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----- Original Message -----
From: "William Smith" <w_smith@...>
To: <
[email protected]>
Sent: Monday, June 28, 2021 5:46 PM
Subject: Re: [nanovna-users] I/O RF Matching net-works measuring with NANO-VNA #applications
Aside: not sure why you are biasing the input, looks like the transistors are already biased on thru BYI-1F, and the input is capacitively coupled.
At the very least the B-E junction of a transistor changes its¡¯ capacitance when you bias it on, no?
William Smith
ComputerSmiths Consulting, Inc.
w_smith@...
On Jun 28, 2021, at 9:57 AM, Peter <yliroma@...> wrote:
?Thanks to eveyone gave an answer ...
Of course I realize the Bias is affecting the Input (and output) impedance of any device ... BUT WHY ???
I intend to highlight my P.A. is a A/B Class RF Amplifier equipeb by two parallele transistor coupled somehow:
Attached the schematics : it is a surplus (ex milititary) unit which was working originally in AM mode ... the related
Bias is obtained via a paritcular DIODE ...
For those who think DC Power-Supply introduces some extra impedance: this not true .. all +Vcc Supply lines are grounded by the CPs capacitors and RF is blocked by the JAFs...
See the attached schematics.
At any rate I have to connect my NANO-VNA when the system is Power-supplied ... ISN'T IT ???
Peter
----- Original Message ----- From: "schweppe" <schweppe@...>
To: <[email protected]>
Sent: Monday, June 28, 2021 1:38 PM
Subject: Re: [nanovna-users] I/O RF Matching net-works measuring with NANO-VNA #applications
Hi Peter,
every amplifier (Transistor or Tube) will change its input (and output)
impedance due to bias. So input (and output) impedance of impeadance
matching network as shown in your picture will also change when bias to
the amplifier is supplied.
73, Guenter, DK5DN
Am 28.06.2021 um 10:02 schrieb Peter:
Hi there ...
Appreciating several features of this incredible instrument, I'm attempting to check the real Impedance of the Matching network INPUT (and/or out-put) value associated to a VHF RF Amplifier (medium-power abt 200W) ... I connected the VNA as shown on the picture and then, after related calibration, I perfomed the measure (sweep)....
Of course I didn't apply any RF source at input ... Nano-Vna only !
I found a strange Resonant Frequency ... quite far from the proper one (I expected to be around 140MHz...150MHz) .... But then , if I apply the related Power-Supply (including BIAS) , the situation changed ... the resonant frequency was really close to the expected one !
Is it normal ?? Really the Power-Supply/Bias could affect impedance values of Input matching net-work ?? This situation can be applied at Out-Put line as well ??
Peter