Topband: BOG pre amp info ?

[Lee STRAHAN]

 Hello Tim and all.
     The input impedance of the W7IUV amp is also highly dependent on the negative feedback found by looking at the unbypassed base bias circuit. And highly dependent on the size of the unbypassed emitter degeneration resistance.
There is a thorough discussion of this by Wes W7ZOI in the ARRL book "Experimental Methods in RF Design". 
Lee   K7TJR   OR

>Input impedance on the W7IUV preamp is determined almost entirely by the DC bias currents.

>Clifton Labs used to have a really nifty set of pages on modeling and measurement of the various high performance preamps. I really miss that site.

>Tim N3QE

On Mon, Nov 27, 2017 at 9:46 AM, Roger Kennedy < roger at wessexproductions.co.uk> wrote:

> Hi Don
>
> Gosh, really?  Looking at the circuit, and given the resistors used, I 
> would have thought the input impedance would be about 800 ohms . . .
>
> And hard to estimate the output impedance, but wouldn't have thought 
> it was about 50 ohms.
>
> Guess I'm wrong then !  Sorry about that.
>
> (I already built a FET pre-amp for my Loop . . . but was just 
> commenting.)
>
> 73  Roger G3YRO
>
>
>   _____
>
> From: Don Kirk [mailto:wd8dsb at gmail.com]
> Sent: 27 November 2017 13:09
> To: Roger Kennedy
> Cc: topband
> Subject: Re: Topband: BOG pre amp info ?
>
>
>
> HI Roger,
>
>
> You said "However, the circuit seems odd . . . I used transformers in 
> and out on my Loop Preamp, to give a match to 50 ohms."
>
>
> I believe your above statement was in reference to the W7IUV preamp.  
> I've measured the W7IUV preamp input and output impedances and also 
> modeled the W7IUV preamp using LTspice, and both methods yield input 
> and output impedances of close to 50 ohms.  Therefore no additional 
> components (such as matching transformers) are required for impedance 
> matching purposes on the W7IUV preamp.
>
> Just FYI,
> Don (wd8dsb)
>
>
> On Mon, Nov 27, 2017 at 5:36 AM, Roger Kennedy 
> <roger at wessexproductions.co.uk> wrote:
>
>
>
> That's a nice cheap board, and worth using considering it has relay 
> switching too . . .
>
> However, the circuit seems odd . . . I used transformers in and out on 
> my Loop Preamp, to give a match to 50 ohms.
>
> Roger G3YRO
>
> ------------------------------------------------------------
> ---------------
>
> Try this guy he does good quality boards and it's easier than 
> importing from the states,
>
> https://m.ebay.co.uk/itm/
> <https://m.ebay.co.uk/itm/W7IUV-Beverage-preamplifier-
> PCB-for-experimenters-
> 2N5109-or-DCP68-transistor-/261634019988>
> W7IUV-Beverage-preamplifier-PCB-for-experimenters-2
> N5109-or-DCP68-transistor-/261634019988
>
> Trevor
> EI2GLB
>
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