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Re: Making a Q-meter /

 

I'm putting together a toy box of various parts, as I plan to make a self contained Q-meter.

I'm just?about to begin an RF sweep of the impedance converter / transformer?driver.

I used an isolated BNC chassis socket for the output, so I have the option of returning the zero-volt drive line to chassis inside the impedance converter / driver.

?I used two 2N3866s as I have several of them to hand.

The 50:1 transformer is a straight copy of the ON7CH one posted by him a few days ago (Thanks for the help, Guido!). It is built in a small offcut of 22mm copper water pipe and uses?50 turns on a T62-2 toroid..

?The single turn secondary is a piece of semi-rigid coax.

Pete
G4GJL


On Sun, Sep 18, 2022 at 8:13 PM John KN5L <john@...> wrote:
Hi Mikek,

The attenuators should not alter "Impedance Converter" output impedance.
The attenuators should have constant output impedance. Guessing
attenuator impedance is 50 ohm, based on R1 = 56.2 ohm. Steve, did you
measure input impedance of your Q1 Q2 demonstration board?

Today, we would use one of the several coax IC buffer amplifiers
available, for the "Impedance Converter Ass'y", as shown at bottom of:
"Q-Meter Prototype Schematic" using an AD8055.

John KN5L

On 9/18/22 12:53 PM, Mikek wrote:
> On Sat, Sep 17, 2022 at 03:06 PM, MAX wrote:
>
>? ? ?The output impedance of an emitter follower is the source impedance
>? ? ?driving the base divided by the current gain of the transistor plus
>? ? ?one.? This value is in parallel with any resistors that may be
>? ? ?connected to the emitter either DC or AC coupled.? So it goes back
>? ? ?to the impedance of the generator that is connected to J6.
>
> For those playing along, Here is a drop box schematic put together from
> the Oscillator to the injection transformer. I was thinking it may help
> to see the impedances.
> I don't have a clue what the attenuator does to the output impedance of
> the RF Power Amplifier.
> ?If I got something wrong notify me, and I'll correct it.
>





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